Darwin's students

2009-06-17T21:05:00.000-07:00

Tay-Sachs disease: Origin and Prevention

Tay-Sachs is an autosomal recessive disease most commonly found in Jews of Ashkenazi descent. Approximately 1 in 30 Ashkenazi Jews in America are carriers for the disease compared to 1 in 300 for the total population.Tay-Sachs is caused by a single mutation in the gene coding for the enzyme beta-hexosaminidase A, resulting in the accumulation of excess ganglioside GM2 in nerve cells of the brain. In the first year of a child’s life they may experience symptoms such as; blindness, deafness, dysphasia, muscular atrophy and paralysis.The child will slowly deteriorate and will most likely die by the age of 4. Another, rarer form emerges later in life and may result in an unsteady gait and neurological deterioration. The characteristic sign of the disease which was noticed by Tay himself is the appearance of ‘cherry-red’ spots in the eyes.

Origin

There are several theories to explain the prevalence of Tay-Sachs in Ashkenazi Jews; one of the more popular theories is the founder effect. In this hypothesis, it is believed there was originally a low incidence of the mutated allele in the Ashkenazi population.Then by a presently unknown cause a large number of people in the population without the allele died. Therefore there was now a higher proportion of people with the defective gene. Once the population re-grew to its original size there was a higher number of people with Tay-Sachs than before. However the founder effect requires certain criteria in order to take place.Firstly, the sudden population decrease must be followed by little or no migration or interbreeding with other societies. Also, being a carrier of the Tay-Sachs allele must not affect a persons chance to reproduce.

A second theory known as heterozygous advantage, is where there is a selective advantage for carriers of the allele. The most widely held theory is that the allele for Tay-Sachs gives the carrier a resistance against Tuberculosis, so those with the alleles have a higher chance of surviving an outbreak of TB. As a result of this resistance the prevalence of the lethal allele increases after every TB outbreak in the Ashkenazi population.

A third theory is genetic drift, which describes random events that cause some alleles to become more prevalent than others, irrespective of environmental or sexual selection . (You may find it interesting to know that Darwin was unaware of genetic drift and therefore evolutionary biologists are no longer known as Darwinists). For example, if by chance carriers in a given generation were to breed more than non-carriers, you‘d expect the prevalence of Tay-Sachs to increase in the next generation.

The final theory is that parents that have a child displaying the Tay-Sachs phenotype may have more children than normal to ensure that they have at least some children that reach a reasonable life expectancy. This means that there may be higher prevalence of the allele in future generations.

There are reasons (which I am about to explain) why most of the theories I have described may not be viable:
Ashkenazi jews have a higher gene frequency of 22 listed genetic disorders, therefore if the founder effect were to be a prevailing theory, early Ashkenazi ancestors must have been carrying several defective genes, this is an unlikely event making the founder effect an untenable theory.
Another problematic theory is heterozygous advantage, in a study by B Spyropoulos et al. data was found that has shown grandparents of Tay-Sachs carriers die from proportionally the same causes as those grandparents of non-carriers. This suggests there is no advantage of being a carrier regarding resistance against any cause of disease, including TB. Also , in another study (Shaw and Smith,1969) it is said that if theTay-Sachs allele offered resistance to TB it would take 300 generations to reach the current frequency of the detrimental allele in the Ashkenazim, who have been a separate group for only 70 generations. In addition one would expect that if TB gave significant resistance, other ethnic groups under comparable conditions would also have a higher prevalence of Tay-Sachs. Similarly, it is doubtful that the genetic drift theory acts alone, because it is unlikely that random chance could produce such a large prevalence of Tay-Sachs in so few generations of Ashkenazi jews compared to the rest of world . A good example of its large prevalence (mentioned earlier), is the united states of America, where the prevalence of Tay -Sachs is 10 times higher is the Ashkenazim than the total population. However, this theory could contribute to other theories and increase their effect.
Finally, with respect to the final theory I described tt is impossible to prove/disprove carrier parents had more children, although it is a seemingly viable hypothesis.
Many theories exist explaining the disease’s prevalence but it is difficult to prove/disprove them. Further research needs to be done but is likely there will never be definite conclusion.

Prevention

Currently, very few methods exists for the prevention of Tay-Sachs. One of the most popular methods for prevention, whilst still having the opportunity to have children, is genetic testing. By receiving information that evaluates the probability of having affected children, parents can make an informed decision as to whether having children is the right decision or not.Pre-natal testing is also available for pregnant women, it allows pregnant women to get tested to see if they are carrying an affected fetus. This gives the pregnant women and her partner the option to have an abortion because they know it is affected.Of course, there are othzer options including abstinence, contraception and chemical castration. Perhaps in the future gene therapy may be a legitimate mode of Tay-Sachs prevention.Research is currently being done by researchers (from 6 prestigious academic institutions) of the Tay-Sachs Gene Therapy Consortium to test whether vectors can be used to transport therapeutic genes into a few diseased cells in the brain. The aim of the therapy is to produce a compensatory amount of Hex B enzyme to be distributed about the entire brain. In practice it should ideally restore the brains ability to function properly.

References

http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1685578&blobtype=pdf
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1685035
http://www-personal.umd.umich.edu/~jcthomas/JCTHOMAS/1997%20Case%20Studies/S.%20Bergeron.html
http://www.curetay-sachs.org/gt.shtml

Why do human females experience the menopause?

2009-06-17T15:10:00.000-07:00

Oxford Concise Medical Dictionary defines menopause as the time in a woman’s life when the ovaries cease to produce an egg cell every four weeks, menstruation ceases and the woman is no longer able to bear children.
In UK, the average age for a woman to reach menopause is 52 years. The question is why do human females experience the menopause? In my research, I have come across two main popular lines of thought. So what are they?
The first idea is the theory of programmed senescence where reproductive cessation is an inevitable outcome of aging. This is linked together with the idea that genetic traits for reproductive cessation have always been present in the population but because in the past, women did not live as long as they do now, menopause was not as evident then as it is now. Doubts about this line of thought arise from the fact that menopause occurs so much more earlier in life compared to other physiological declines such as senility. Furthermore, if this was all there was to explain the menopause, then would this not mean that the same consequences would apply to the male population? This leads to the second main idea proposed which is known as “evolutionary adaptation”.
This idea suggests that menopause occurs in order to increase the chances of the survival of the mother, her offspring and her grandchildren. To explain further, the risk of death of the mother during childbirth increases with the maternal age. Therefore the menopause could be potentially viewed as a safeguard for the mother and her offspring. The mother will not be exposed to the increased chances of death during childbirth in her older years and the children are less likely to perish from lack of maternal protection and care. This also means that the post-menopausal woman will be available to help her daughters to look after her grandchildren and further promote the chances of their survival. A study supporting this theory is that of African hunter-gatherers. It suggests that post-menopausal women are able to provide food and because of this, their daughters are able to breast feed for a shorter time and have more babies during their fertile years. However this idea could be viewed from another perspective, where the fact that the post-menopausal woman is available to look after her grandchildren is a side effect of her menopause and not a cause of it.
A further idea to this theory of evolutionary adaptation is, in the case where there was no grandmother to help the daughter, menopause ensures that a woman cannot have so many children, that the abundant number prevents her from providing adequate care to some of her other children and so putting them at risk and decreasing their chances of survival. An argument that has arisen from this line of thought is that if the menopause is used as a way to ensure that a woman should not be overwhelmed by having too many children to look after, then would it not have been more plausible for a woman’s body to be sensitive to her levels of stress and thus have prevented further pregnancies at that particular time?
In my opinion, the theory of senescence, evolutionary adaptation and also the role of the post-menopausal woman all offer partial plausible explanations as to why human females experience the menopause. I do feel, however, that none of them could individually be used as a complete explanation to this question and probably the answer would involve a combination of all three ideas. While agreeing on the most part with all the three ideas, I am inclined to feel that the role of the post menopausal woman is slightly weak, as that role could just have easily been taken on by the father of the children.
Resources
Oxford Concise Medical Dictionary (7th Edition)
Natural History (Craig Parker)
Evolution of Human Menopause (Shaneley DP and Kirkwood TB)
National Institute of Aging
Hawks K, The Grandmother Effect. Nature 2004

Has human evolution stopped?

2009-06-17T13:09:00.000-07:00

The human family, the Hominidae separated from the apes around 5 to 7 million years ago and the modern human species, the Homo sapiens appeared in East Africa around 200,000 years ago. However, it is difficult to know whether we have evolved a great extent since then. We must consider the fact that evolution acts on many different levels; through natural selection, sexual and kin selection etc. Natural selection is mediated by the environment and is primarily for improved survival in the prevailing conditions of the time. Sexual selection however is exerted by other members of the population so that they can mate with individuals who they believe to have preferential traits while kin selection is a process sometimes directed by individuals towards their relatives, a kind of altruism which allows reproductive success of their relatives. These, especially natural and sexual selection are external forces ultimately dictating the speed of evolution by increasing or reducing allele frequencies on the basis of their reproductive benefit. However, they may be impeded by genetic drift which sees to alter gene frequencies on the basis of random distribution of parental genes in the offspring which introduces an element of chance. The effects of genetic drift are more pronounced in large populations due to the increase in the possible combinations of genes. Because evolution is a trade off between natural selection and genetic drift, one dominates over the other depending on how strong selection pressures on a particular locus are to cause gene frequency shifts.
One reason that has emerged to suggest that human evolution is stopping or slowing down is based on the huge increase of our population on the evolutionary scale and in recent times. Figures from February 2009 suggest that the world population has now reached 6.7 billion and for example, for a British child, there is a 99% chance that it will reach its reproductive age compared to 500 years ago when this was only 50%. Large populations have a higher stability than smaller ones as newly arising mutations will be swamped by the already established genes. Therefore, mutation rates of genes can be high but retention in the population will be more difficult. Another point is that although the acquisition of point mutations are fairly constant, DNA has repair mechanisms to allow retainment of its original condition.
Steve Jones, a geneticist at UCL, has argued that natural selection is no longer important for humans. Since it works by ensuring the survival on those who are more reproductively successful, through medical intervention, we have altered this so that nearly anyone in the population can have a child. He therefore believes that human evolution has indeed stopped. However, saying that natural selection is no longer significant among humans is not necessarily correct.
Since the transition from hunter-gatherer behaviours to more agricultural (and technological) ways, we have developed characteristics specific to this. For example, once people began rearing cattle, gaining milk derived nutrition spanning life, instead of it being halted at the infant stage, became advantageous which gave rise to lactose tolerance. Due to this, presently, the gene for lactose digestion appears in 80% of Europeans. However, for Steven Pinker, author of ‘How The Mind Works,’ the emergence of culture meant a move towards ‘non-genetic means to adapt’ for example through behavioural changes.
One of the greatest triumphs of our species was to develop consciousness. Consciousness is something very difficult to define however. When faced with a stimulus, we can retrieve information from past experience to relate to the present situation and make a conditioned response. However, other animals can also do this. We on the other hand can also register the event as being pleasant or not i.e.have an emotional response to it to trigger goal states. In this I mean we can then decide ourselves which course to take after this. Therefore, objects can become things of desire and increasing our experience of them may lead to an enhanced potential for survival and reproduction in the environment. This step in our reaction introduces the state of being self aware due to the level of control consciousness has allowed us to have. Self awareness is also a prerequisite for the understanding of others and manipulation of the environment, which is what we have achieved and also, the formation of culture. 50,000 years ago tribe formation because of this and new hunting techniques with the invention of tools because of increased intelligence allowed the number of tribes in an area to proliferate and in doing so increase opportunities for social interactions.
Humans have also developed left-right asymmetry of the brain which apes do not show. The importance of this is that besides the opposing sides of the body being controlled by the opposite hemisphere, the two hemispheres also differ in their functioning. For example often the left is the dominant which specialises (on average) in logical and sequential/mathematical reasoning. The right is related to more artistic abilities such as shape and colour recognition (e.g. faces) i.e understanding patterns. The development of these features has given a new course for selection pressures to act on. However, not just on single genes as intelligence and increased congition etc. are caused by interactions of a variety of genes. Selection pressures however can seek to form an optimal combination of genes. Therefore, many would argue that in fact human evolution is accelerating by cultural development through these means and creating behavioural change. Increase in urbanisation and technology through our ingenuity has meant as Ian Tattersall put in ‘Becoming Human: Evolution and Human Uniqueness’ that ‘we are being besieged by social stimuli’ so this is what we are adapting to.
In our evolutionary history, it has been found that instead of gradual allele frequency shifts (phyletic gradualism) causing change, there were periods of species stability interrupted by speciation, extinction and replacement –punctuated equilibrium, which was put forward by Niles Eldredge and Stephen Jay Gould in 1972. They found that a new species can be created from a pre-existing one when the selection pressures are large and the species is able to adapt, speciation occurred as a short-term process compared to in phyletic gradualism. Therefore, there is little evolutionary change during most of their history but when evolution occurs, it is rapid and short-term. If the pre-existing population is divided due to a physical barrier, caused by anything such as a seaway, the population begins to diverge and because smaller gene pools are less stable, speciation occurs even faster. Therefore, there is little evolutionary change during most of their history but when evolution occurs, it is rapid. However, in ‘evolutionarily recent’ times, we have found means to overcome physical barriers such as seaways and terrestrial barriers such as mountains etc. and therefore, we are becoming more uniform in our species with the human population being constantly mixed . It has therefore been put forward that we are tending towards a ‘uniformly brown-skinned population.’However, Robert Moyzis at the University of California at Irvine believes that due to the accumulation of various SNPs (single nucleotide polymorphisms, single base changes) in certain populations, we are diverging because of the differences between races.
Therefore, there are many theories as to what will happen in our evolutionary future. Many focus on cultural changes due to behavioural development and others on morphological change. However, it is very unlikely that human evolution has stopped. This would mean that the mechanisms for evolution no longer apply to us which separates us from the rest of the animal kingdom and seems to single us out as being special when in fact we arose the same humble way that other creatures have. We cannot say that we are improving either as this would commit evolutionary fallacy that each stage if evolution works to improve us. Evolution seems to act on many levels and it is difficult to predict what direction it is heading as it is essentially blind. Therefore we also may not be able to rely on our past evolutionary history as a means to put light on the future.
Bibliography
Becoming Human: Evolution and Human Uniqueness, Ian Tattersall, Oxford University Press, 2000
How The Mind Works, Steven Pinker, Penguin, 1998
Human Evolution; an Illustrated Introduction, Roger Lewin, Blackwell Publishing, 2005
Cells, Embryos and Evolution, John Gerhart and Maarc Kirschner, 1997
http://www.scientificamerican.com/article.cfm?id=the-future-of-man
http://www.newscientist.com/article/mg18925421.300-are-we-still-evolving.html?full=true&print=true
http://www.timesonline.co.uk/tol/news/uk/science/article4894696.ece

Comparison of the sexuality of Humans, Common Chimpanzees and Bonobos

2009-06-17T11:33:00.000-07:00

When first considering this title, it may seem a bit perverse to be delving into the details of human, chimpanzee and Bonobo sexuality. However, when considering Darwin and the theory of evolution, it is integral to discover the mating habits and social norms of all species, especially ones that are so closely related to our own, in order to further our understanding of human evolution. Homo sapiens, the Common Chimpanzee and Bonobos, otherwise known as pygmy chimpanzees, all share a common ancestor. Between these species, there are many noted areas of similarity and disparity within behaviour and physical appearance. One area that has been of particular interest to many researchers is that of social sexual behaviour. Well known
Homo sapiens are usually set apart from other mammals due to our ability to conduct ‘higher thought’ processes. Nevertheless, social sexual behaviour is also a major characteristic that separates humans from most other species. Sexual behaviour of humans is fairly distinct because they are not sexually active solely for reproductive purposes. In the human community, sexual intercourse also plays an important role socially, by creating strong bonds between individuals by increasing physical intimacy, it is the foundations of many social hierarchies and there is also a hedonistic factor as enjoyment of the activity is a large driving force behind copulation. Evidence to support this in humans, is the creation of contraceptive techniques. Humans not only have sexual intercourse when procreation is not intended, but they go one step further and take measures to ensure that reproduction is actually prevented. This is a behaviour that is almost certainly unique to the human species, even if sex as a social role is not. Bonobos are another species that uses sexual intercourse in a social context, with the same benefits as humans, such as stronger bonding and social hierarchies. It also has been seen to maintain a more peaceful environment amongst their community as aggression amongst the males can be vented through sexual acts. Atypically for species in the mammal genre, the female Bonobos are hierarchically more dominant.5 It has been theorised that this is due to the bonds that are formed between females. Wrangham, a leading primatologist, hypothesises that this grouping of females is a counter strategy to the male reproductive strategies as groups of females are greater at attracting groups of males.1 On the other hand, the Common Chimpanzee do not hold the same principles of social sexual behaviour and society tends have a more aggressive atomosphere. The Common chimpanzees have a patriarchal society where the males are dominant and, as with most animals, sexual intercourse is purely for reproduction and advancement of the species.
The Bonobos and the common chimpanzees, are part of the same genus and have many similarities mainly physically and biologically, an example being the female swelling cycle. Impending ovulation the sexual skin surrounding the perineum of the female primate, swells and reddens, and is usually shows a conspicuous maximum tumescence around the presumed time of ovulation.4 Studies have shown that in both species this swelling has a direct affect on the sexual arousal of the males. This has the obvious evolutionary advantage of attracting males sexually, when the female is most fertile. The results of the studies, show that the Bonobos seem to have a longer span of maximum tumescence compared to the common chimpanzees, although this could be a discrepancy of only 1-3 days. With this in mind, another point of comparison that could be addressed is that of the cycles of arousal between the species. In humans, sexual arousal for females is not limited by the time of ovulation as it is with most other mammals, there are only periods of heightened sensitivity. This supports the idea of a more socially orientated sexual behaviour as sexual intercourse can be initiated at any point. Bonobos are similar to humans in this instance, although they have a more obvious display of when they are at maximum tumescence. Unlike the common chimpanzees, instead of a few days out of her cycle, the female bonobo is almost continuously sexually active and attractive.
The position of sexual intercourse is one of the more shocking similarities between Bonobos and Humans. In contrast to most other primates, the Bonobos mate in what was long considered to be a uniquely human fashion. Their sexual activities vary in position and sexual contacts, including face to face copulation. The common chimpanzees have a more typical mating ritual which is generally associated with mammals, with the male approaching from behind the female. Female bonobos also partake in a sexual activity known as genito-genital rubbing, where the two females rub together their gential swelling laterally together. It is thought that this female-female interaction helps reinforce the strong bonds between the females and contributes to the female dominance.2 Females amongst the common chimpanzees are not so well attached and so such activities do not take place in this species’ communities. Male bonobos have also been seen to participate in homosexual activities. Examples are where one male briefly rubs his scrotum against the buttocks of another. Another example is the phenonmenon of ‘penis fencing’ whereby two males hang face to face from a tree while rubbing their erect penises together.2 It is unsure what benefits such acts of homosexuality can have, seeing as there is no reproductive advantage, however one explanation available is that it is a way of resolving disputes amongst individuals of the group as an act of peacemaking. There has also been some evidence of masturbation by both female and male bonobos, an action that is almost unheard of outside of a human context. This fact serves to further prove the idea that the bonobos enjoy a highly sexually based society.
Finally the most significant difference between humans and the two species of chimpanzee is the tendancy to only have one sexual partner at a time. This is not a behaviour that it found amongst the primates as each female and male have multiple partners.6 In the wild this has its advantages as it lowers the occurance of infanticide by males as there is no way of being sure which male the offspring belongs to. Also, unlike most species in the animal kingdom, the time when a person reaches physical maturity is not directly correlated to when a person first takes part in sexual intercourse.
In conclusion, Humans, The common Chimpanzee and Bonobos, despite being derived from a common ancestry have very some very different social behaviours concerning sexuality. Out of the three species Bonobos and Humans arguably have the more similar behaviours as their community as a whole largely revolves around a sexual concept. Sexuality moulds the way Bonobos interact with eachother as it does within human society. Even the way the act is carried out greatly resembles that of humans. The only major difference is that humans usually maintain a single partner throughout life, and tends to only reproduce with that partner, whereas the primates have multiple partners. Also as soon as the primate reaches physical maturity, they are then expose to sexual activities, whereas this is not necessarily the case in homo sapiens.

1 WRANGHAM, R.W. 1980. An ecological model of female-bonded primate groups. Behavior 75: 262–300
2 Bonobo Sex and Society Scientific American March 1995. FRANS B. M. DE WAAL
3Comparison of behavioral sequence of copulation between chimpanzees and bonobos Received: 30 August 2004 / Accepted: 22 January 2005 / Published online: 16 September 2005 by Chie Hashimoto and Takeshi Furuichi
4Perineal Swelling, Intermenstrual Cycle, and Female Sexual Behavior in Bonobos (Pan paniscus) American Journal of Primatology 68:333–347 (2006) by T. Paoli et al
Female Reproductive Strategies as Social Organizers DIANA PRASCHNIK-BUCHMANa Hunter College of CUNY, New York 10021, USA
5The Other “Closest Living Relative” How Bonobos (Pan paniscus) Challenge Traditional Assumptions about Females, Dominance, Intra- and Intersexual Interactions, and Hominid Evolution by AMY R. PARISH AND FRANS B. M. DE WAAL- ANNALS NEW YORK ACADEMY OF SCIENCES
6 http://news.softpedia.com/news/The-War-Ape-The-Sex-Ape-69208.shtml

The illness of Charles Darwin: a retrospective diagnosis.

2009-06-17T10:45:00.000-07:00

The topic of this blog is the much debated illness of Charles Darwin. Firstly, an effective clinical history of his illness will be attempted, describing and classifying the symptoms. Then, possible explanations for his collection of symptoms will be addressed; including previous attempts to explain his illness.

Before 1837, Charles Darwin had, considering the poor level of medical knowledge and sanitation during the period he lived in, quite good health. He suffered from scarlet fever when he was nine and developed a mouth infection at college prior to his travels aboard the Beagle, both fairly inconspicuous illnesses for the time. Furthermore, during his five year round the world trip, he was taken seriously ill on only one occasion, which he attributed to food poisoning. It is surprising, when the extreme conditions he would have endured aboard the Beagle are taken into account that he did not suffer from illness more often during the five year voyage. There are those who claim that Darwin suffered from symptoms prior to his voyage on the Beagle and that there is evidence for a genetic disorder. However there is a far greater consensus that Darwin only began to experience the symptoms of his disorder after his return.

This good health contrasts sharply with Darwin’s health after 1837. It was at this time in his life, (when he was aged just 28) when he started to suffer from the collection of symptoms that would plague him until he died in 1882 (aged: 73.) They began with fatigue, malaise, stomach cramps and headaches, but worsened throughout his life: including worsening neurological symptoms like tinnitus, dizziness, sensitivity to temperature, further headaches, muscle spasms and tremors; as well as worsening gastrointestinal symptoms such as vomiting and colic. Furthermore, he developed cardiovascular and respiratory symptoms such as palpitations and shortness of breath. He also went on to develop dermatological symptoms such as blisters and ulcers. All of this was also accompanied by bouts of anxiety and depression.

In terms of the character and pattern of these symptoms, whilst it is true to say that the symptoms were most severe towards the end of Darwin’s life, it is not true to say they followed a progressive pattern of disease. It appears that Darwin’s symptoms took on a remitting/ relapsing character; where he had periods of relative health followed by months of illness so severe that he was bedridden and unable to work. Furthermore, stress appeared to exacerbate his condition. Indeed it is said his period of worst health was 1847-1851. This was a period of great stress. Both his father and “favourite” daughter (Annie) died; Annie aged just 10 at this time. In addition, within this period, his closest friend and scientific confidant, Joseph Hooker, left on an expedition to the Himalayas for three and half years. This was devastating news for Darwin who was relying on Hooker for fine tuning his book. Another noted exacerbating factor was preservative chemicals, Darwin’s health would tend to deteriorate when performing experiments (with chemicals). The one apparent alleviating factor was Dr. James Gully’s water cure establishment in Malvern. Darwin was persuaded to attend by his wife Emma, and stayed for four months instead of the proposed three weeks. The treatment was mainly homeopathic and probably had no effect, but another component of the ‘cure’ was a ban on alcohol, rich foods (including dairy) and tobacco as well as compulsory walks. This would have likely improved Darwin’s health.
Some have tried to explain Darwin’s illness as stemming from psychological problems, the eminent psychologist John Bowlby suggested that it was somatisation (psychological problems and emotional trauma being expressed as physical symptoms) caused by a suppressed grief for the loss of his mother. However, the extent to which Darwin suffered from the symptoms and his relative detachment to his mother, suggests that this is no the case. Another psychological explanation for Darwin’s illness was that it was mainly caused by stress that accompanied the guilt and internal conflict he felt towards his own work towards: ‘On the Origin of Species,’ as he was fully aware of its religious implications as well as how many of his colleagues and friends would react. There is support for this in the timing of the onset of his symptoms around the same time as he began work on his book. However, the severity of the symptoms he experienced surely cannot be accounted for by such a theory.

One possible suggestion for Darwin’s illness, which is based on the effect of the Malvern water treatment, is that he was lactose intolerant, as the improvement seen would have been caused by the dairy free diet at the establishment at Malvern. Furthermore, in this disease patients have chronic gastrointestinal symptoms if lactose is not removed from the diet, which chronically can cause malabsorption in the gastro-intestinal tract potentially causing neurological symptoms due to ion imbalance within the blood. However, even if we make a significant assumption in that the cardio-respiratory symptoms are caused by a separate environmental heart disease, it cannot explain the more severe of his neurological symptoms, his dermatological symptoms or indeed his fatigue.

Another, potential explanation also focuses on gastrointestinal disease. Some have blamed Crohn’s disease; the main strength of this argument is that it fully explains the gastrointestinal symptoms as well as explaining the relapsing/ remitting pattern of his disease. Furthermore, stress is known to have a role in the onset of an acute episode in Crohn’s sufferers, as is the case with Darwin’s symptoms. In terms of the dermatological symptoms Crohn’s can typically cause apthous ulcers of the mouth and other skin disorders. However, this explanation also falls down in effectively explaining the cardio-respiratory symptoms as well as the neurological symptoms. Unless as with above they are attributed to stress or other incidental disease.

A further, much popular hypothesis (endorsed by Sir Peter Medawar), is that he contracted a parasite that caused chronic Chaga’s disease after being bitten by the Triatoma Infestans bug. This disease may have gastrointestinal manifestations as well causing heart problems and the neurological symptoms could be explained as being secondary to the other symptoms or indeed a response to chronic disease. However, the dermatological symptoms described are less easily attributed to Chaga’s, although they could potentially be linked to the immune response that is believed to cause most tissue damage in Chaga’s. There is further evidence against Chaga’s, in that usually, chronic exposure to the bug’s faeces is needed to cause an infection. A factor not present in Darwin’s case.

Perhaps the most important factor to draw from these attempts to diagnose Darwin is that the more popular explanations are all linked to the immune system, and produce their effects at least in part by an inappropriate immune response. This has lead some to believe that Darwin suffered from multiple allergies, Fabienne Smith the foremost among them. This is supported by the fact that much of Darwin’s family had some sort of allergy and the death of his daughter Annie appears to be a total immune collapse. In addition the stress and chemicals that exacerbated his symptoms are typical in an allergic condition.

In conclusion, whilst there are many compelling arguments for different causes of Darwin’s symptoms, and a significant volume of information on his symptoms, and eventually there may be a popular consensus as to his illness; it will never be possible to make a definitive diagnosis.

Bibliography:
http://www.darwin-legend.org/html/darwins-illness.htm
Campbell AK, Matthews SB. Darwin's illness revealed. Postgrad Med J. 2005 Apr;81(954):248-51.
The Rough Guide to Evolution by Mark Pallen
Darwin: A Life in Science by John Gribbin and Michael White
Kumar and Clark Clinical Medicine by Kumar and Clark

Charles and Emma- Benefits and Hazards of First Cousin Marriages

2009-06-17T10:29:00.000-07:00

At first glance this title seems to have a rather tenuous link to Charles Darwin unless you were aware that Charles Darwin married his first cousin Emma Wedgewood and was plagued with fears throughout his life that he had left his children with a ‘genetic time-bomb’. Emma and Charles shared a common grandfather Josiah Wedgewood and were born of brother and sister; Josiah Wedgewood II and Susannah Wedgewood respectively. They went on to have ten children but three died in childbirth, Mary Eleanor less than four weeks from birth, Annie (known as Darwin’s favourite child) at 10 years and Charles Waring at 6 months (1). Currently it is generally legal for first cousins to marry in most western societies, with only the USA notably banning the practice, 31 states make this practise illegal (2). Over recent times, the tradition of marrying first cousins, a practice favoured by the elite in early centuries in an attempt to not dilute the blood line and limit the claimants to family money, is becoming less common with increased transport and communication ensuring a larger population of prospective mates (3). However it is still believed 80% of marriages historically have been first cousin marriages, and are still prevalent in some societies; 3 out of 4 marriages in Bradford’s Pakistani community are inter-cousin unions(4).
It seems when debating views on first cousin marriages the scientific hazards and benefits need to be considered along with the ethical and social consequences. Darwin’s Origin of Species (5) explains evolution as the variation, non constancy of species giving them advantageous characteristics allowing them and in turn their offspring to survive, inheriting these characteristics, this principle is natural selection. The result of natural selection is gradual change due to the accumulation of heritable advantageous traits. The principle of descent with modification offers an explanation for some specie becoming extinct whilst others continue, it also explains Darwin’s tree of life; all living organisms come from common ancestors. Many theories of benefits of first cousin marriages relate to the belief that by doing so they are following the principles of evolution. The belief in common ancestors leads to belief in a continuum of animals and humans and the ultimate question, what separates humans from our ancestors, chimps; chimps mate within a community (6) therefore it is highly likely they mate with first-cousins indiscriminately, so at what point does it become our decision to actively choose a mate due to social and legal rules as opposed to the one nature causes us to be attracted to? At what point do the ‘rules’ for us choosing an appropriate mate become different to those of a chimp?
In addition sexual selection (5) is the struggle within the same sex of the same specie to ensure they mate with the partner with the most desired characteristics giving their offspring maximum chance of survival to propagate their specie with characteristics to exploit the resources available. Therefore if an individual has attracted the individual of the opposite sex who could allow them to give their offspring that desired characteristic, why should they be handicapped compared to others in their specie of the same sex as a result of a family relationship with the desired partner? If people are of the same family they may share positive characteristics, thus children born of them may have these positive attributes further exaggerated, should positive eugenics be discouraged?
Furthermore due to evidence from mitochondrial DNA it has been suggested that all humans outside of Africa developed from one branch of the ‘tree’ which left Africa in the ‘African exodus’ 60,000 years ago (5). Therefore it could be argued that as everyone is related anyway and we share more genetic similarities than one sub-specie of chimps there is little point stopping the marriage of first cousins when most marriages are between related people anyway.
From the social aspect, couples will have a stronger network to support their relationship if they are related, they are likely to share the same values and common memories, meaning the relationship is likely to be more successful, therefore more likely to conceive children and continue the specie.
The most common concern related to first cousin marriage is the genetic implications to the offspring. Studies have shown there is an increased risk of congenital malformation caused by homozygosity for autosomal recessive alleles. When estimating the probability a child of first cousins will have an autosomal recessive disease, it is assumed the grandparents each have a recessive mutation, the probability of the child inheriting the grandfather’s mutation is 1 in 64, similarly they have a 1 in 64 chance of getting their grandmother’s, giving a probability the child will be homozygotic for one of the grandparent’s mutations of 1 in 32, which when added to the risk of major congenital mutation in the general public (1 in 40) they have a 1 in 20 risk of developing a congenital abnormality.(7)
A further theory is that nature itself discourages a too close familial relationship between parents, in a study performed at Liverpool University (8) two sets of male mice were used each identical apart from their major urinary proteins, mice born of related parents have less varied proteins than those of unrelated parents. In the experiment the female mice consistently chose mice with more complex proteins suggesting they could detect the consanguinity, it is thought women may also have this ability.
Once again social opinion influences the practise, in western society it may be viewed unfavourably and people may become ostracised from society ‘We have to stop this tradition of first cousin marriages’ Keighley MP Ann Cryer (4).
However before finally weighing up the hazards and benefits of first cousin marriages it must be considered the way in which the scientific evidence of hazards is reached. Often the cultures considered are those which are either isolated, so first-cousin marriages are a higher occurrence than in some societies or in cultures where it is actively encouraged, which could lead to biased results as the children considered would not be just one off children of first cousin marriages, but an accumulation of several first cousin marriages over many generations in history.
Additionally social and economical factors may have an effect, as cultures where consanguinity is in higher occurrence may also be poorer to begin with, so the mother’s possible malnourishment could be a confounding factor (3).
Also the fertility of the children is often used to consider the success (9) of the offspring and therefore the marriage of the parents, but although a child does not go on to have children themselves, they may have success in other areas such as intelligence. For example, Darwin’s’ children; where William was a banker, Henrietta edited and published her mother’s letters and Leonard taught at the school of military engineering yet none of the three had children (10). Also one should bear in mind that it is known that there are increased genetic problems in children of older mothers (1) but this is not illegal or particularly socially unacceptable.
It may also have been noticed that many of the theories offered as benefits to first-cousin marriages are not benefits just justification to why it is acceptable and not a hazard, just a component of natural selection.
In conclusion, in my opinion first cousin marriages within our society should be neither actively encouraged or discouraged as to allow evolution and natural selection, social and legal implications should not intervene with the biological attraction people feel to their mate. If the practise is encouraged it will occur more regularly than nature intends, so the hazards will accumulate. However, if it is discouraged, natural selection is not occurring and people cannot necessarily mate with those with the most desirable characteristics. My concluding opinion is only relevant in our society where the occurrence is so small as not to be deemed a serious hazard, in smaller more isolated communities it may occur at a higher incidence, thus the hazards are likely to outweigh the benefits. Finally it is important to remember that evolution rejects determinism. We cannot predict evolution as some situations just happen; people may choose not to have children, so we cannot try to manipulate nature as we are unaware of the final consequences.

(1)http://roughguidetoevolution.blogspot.com/ (last accessed 16th June 2009)
(2)Brandon Keim- ‘Cousin Marriage OK by Science’- Wired Science December 23rd 2008
(3) Diane B. Paul, Hamish G. Spencer.‘It’s Ok, We’re Not Cousins by Blood’. The Cousin Marriage Controversy in Historical Perspective. www.plosbiology.org
(4) Rowlatt J. The Risks of cousin marriage. BBC Newsnight.
(5)‘The Rough Guide to Evolution’ Mark Pallen, 2009
Page 50- The origin of Species: a one page summary
Page 204- Out of Africa
(6) http://library.thinkquest.org/04oct/01878/clife.htm (last accessed 16th June 2009)
(7) Turnpenny P. Ellard S. Emery’s Elements of Medical Genetics 13th edition.
(8)Brandon Keim- Women, Trust Your Nose: Inbred Men May smell bad- Wired Science April 17th 2008
(9) C.D. Darlington. Cousin Marriage and the evolution of the breeding system in man.
(10) http://www.aboutdarwin.com/darwin/Children.html (last accessed 17th June 2009)

The Pleistocene diet: a recipe for diet and health?

2009-06-17T10:07:00.000-07:00

To answer this question I shall begin by giving a brief description of what is meant by “The Pleistocene diet”. Starting with what or should I say when the Pleistocene epoch was in our history. The Pleistocene era is the earlier of the two epochs of the Quaternary Period, from about 2 million to 10,000 years ago, and was characterized by the formation of widespread glaciers in the Northern Hemisphere and by the appearance of humans. Mammals included both small forms, such as sabre-toothed tigers and horses and giant ones, such as mammoths and mastodons. Almost all the giant mammals, including woolly mammoths, giant wolves, giant ground sloths, and massive wombats disappeared at the end of the Pleistocene and the start of the Holocene.

The Pleistocene diet refers to a diet which is similar to that of the humans at that time, without the invention of food preparation or cooking. It’s principle is that it is based around foods that were readily available, “on the table” during our evolution, foods such as meat, fish, fowl, and the roots and fruits of many plants. As whilst food stuffs such as grains, beans and potatoes are useful sources of energy, our bodies are not adapted to utilising them as a food source, as when eaten raw they contain many harmful toxins, so rendering them inedible to our evolutionary predecessors. The Pleistocene diet considers such foods as Neolithic, as they were only edible after the discovery of cooking around 10,000 years ago, and so their ingestion is not “coded for in our genes”. (1)

Furthermore the diet is based around the idea that as much as individual genetics and experiences influence your nutritional requirements, millions of years of evolution have also shaped our need for specific nutrients, that our dietary changes have outpaced our ability to genetically adapt to them, as according to Eaton. "That the vast majority of our genes are ancient in origin means that nearly all of our biochemistry and physiology are fine-tuned to conditions of life that existed before 10,000 years ago.(2)

In comparison with our evolutionary diet, today’s diet fails to meet sufficient biochemical and molecular requirements of homosapians. Evolutionary diet consisted of prehistoric man consuming around 50% of his calories from carbohydrate, mainly from fruits and roots, in comparison with modern times, where carbohydrate often takes the form of sugar and sweeteners and is devoid of essential vitamins and fatty acids.(2) The best available estimates suggest that our ancestors obtained about 35% of their dietary energy from fats, 35% from carbohydrates and 30% from protein. Saturated fats contributed approximately 7.5% total energy and harmful trans-fatty acids contributed negligible amounts. Polyunsaturated fat intake was high, with substantial cholesterol consumption. Carbohydrate came from uncultivated fruits and vegetables, approximately 50% energy intake as compared with the present level of 16% energy intake for Americans. High fruit and vegetable intake and minimal grain and dairy consumption made ancestral diets base-yielding, unlike today's acid-producing pattern. . Fibre consumption was high and Vitamin, mineral and (probably) phytochemical intake was typically 1.5 to eight times that of today except for that of Na, generally <1000 mg/d, i.e. much less than that of K.(3)

The Pleistocene diet was said to include a much greater quantity and variety of fruits and vegetables as well as dietary fibre, which aids in gastro-intestinal health. This is often a criticism of modern western diets, where the quantity and variation of fruit and vegetable intake is much lower and often insufficient to the Palaeolithic, with fewer than 9% having the recommended 5 portions per day.

A further advantage of this diet can be seen to be that it contained a greater ratio of omega 3 to omega 6 fatty acids and also a greater proportion of potassium with a lower Sodium intake, due to a diet containing less processed food.(2)

The diet advocates a high intake of:
Meat, chicken and fish
Eggs
Fruit
Vegetables (especially root vegetables, but definitely not including potatoes or sweet potatoes)
Nuts, e.g. walnuts, brazil nuts, macadamia, almond. Do not eat peanuts (a bean) or cashews (a family of their own)
Berries- strawberries, blueberries, raspberries etc.

Whilst in taking none of the following
· Grains- including bread,
· Pasta,
· Noodles
· Beans- including string beans, kidney beans, lentils
· Potatoes
· Dairy products

· Sugar

· Salt

So is this type of diet nutritionally viable and compliant with today’s recommended food intake?
The food standards agency advocates a healthy diet to be one that contains a variety of foods including plenty of fruit and vegetables, plenty of starchy foods such as wholegrain bread, pasta and rice, some protein-rich foods such as meat, fish, eggs and lentils and some dairy foods. It should also be low in fat (especially saturated fat), salt and sugar.(4)

The Pleistocene diet does seem to meet much of this criteria, in the form of the high content of fruits, vegetables, and protein, and low salt, and sugar intake. However it does not include any dairy products which are said to be included in modern diets.
So in theory the diet does seem suitably nutritious and provides the basis fo a healthy lifestyle, but what effects does it have when applied to modern people?
One study which looked at the short-term effects of such a diet on 14 healthy volunteers concluded that the intervention in their diets did produce some positive effects, namely reduced fat composition, and increased intake of anti-oxidants. The total energy intake was also reduced by 36% and with this the subjects mean weight decreased by 2.3kg, and their BMI also decreased by 0.8, indicating positive effects. However there was also a reduced calcium intake which in the long term could be problematic and further studies must be carried out before a definitive conclusion can be made. (5)

However one problem concerning the Pleistocene diet is its effect on teeth, and that whilst our DNA had not evolved or changed massively from that era to now, the structure and make up of our jaws and teeth have changed sufficiently to make consuming a diet of purely raw, and so often tough food, slightly problematic and predispose the partaker to dental problems.(6)

Over time humans have evolved to have smaller teeth, with a thinner enamel coating which renders them less effective at cutting into, tearing and peeling tougher food stuffs. The reason for these changes in dental structure are rooted not in the lifestyle of the earlier humans in the sense of changing from gathering to producing food, but from changes in food-preparation techniques and non-dietary usage of the teeth.(7)

Casting that issue aside for the meantime though, there are other benefits that this diet provides which can be particularly pertinent for those which long standing chronic condition. Studies have shown that a “prehistoric” diet can be of benefit to those suffering with diabetes and ischaemic heart disease by improving glucose tolerance.(8)

Another positive aspect of this diet is the reduced salt intake, as salt has been linked in with high blood pressure and so a reduction in salt intake from following such a diet can reduce the risk of hypertension.(9)

As well as this foods such as snacks, particularly in the form of energy drinks, which are much more energy dense then many of the foods available to Pleistocene man have been accredited to one of the main nutritional problems of modern society in obesity, as people are often partaking in such snacks and not compensating for them in their diet, leading to a positive energy balance, and from evolution, humans have a weak defence against over eating and so problems arise. So as a Palaeolithic diet is without these items it could also be seen as a healthier option.(10). Also humans are evolutionarily adapted to a calorie restricted diet and to survive in a state of under nutrition, 10, where due to conditions such as increased soil aridity and cooler temperatures, led to a reduction in potential food sources for Pleistocene man, and so they would change or alter the way in which they metabolised their food.(11)

It can be seen that a Pleistocene diet does vary from most modern diets, both in its type and proportion of food consumed. Results have shown that this can be a healthier lifestyle, as the high intake of animal-based foods would not have necessarily elicited unfavourable blood lipid levels due to the hypolipidemic effects of high dietary protein (19-35% energy) and the relatively low level of dietary carbohydrate (22-40% energy). Although fat intake (28-58% energy) would have been similar to or higher than that found in Western diets, it is the case that the proportion and types of fat ingested would have been vastly different with relatively high levels of MUFA and PUFA and a lower omega-6/omega-3 fatty acid ratio, would have served to inhibit the development of CVD.(12)

Therefore the Pleistocene diet, in my opinion is useful as a reference point and provides important clues to the "baseline" levels and ratios of nutrients needed for health. Suggesting that we should be eating a lot of plant foods and modest amounts of game meat, with a reduced intake of salt and refined foods, and despite it perhaps not being practical to follow it to its entirety, with an increased understanding of it, it can aid us to lead healthier and more natural lives, optimizing our surroundings and what our bodies are able to deal with.

(1) Dr. Ben Balzer. Introduction to the Paleolithic diet. Available at: http://www.earth360.com/diet_paleodiet_balzer.html.
(2) Challem J. Paleolithic Nutrition:Your Future Is In Your Dietary Past.
(3) Eaton SB. The ancestral human diet: what was it and should it be a paradigm for contemporary nutrition? Proc Nutr Soc. 2006;1(65):1-6.
(4) Healthy diet. Available at: http://www.eatwell.gov.uk/healthydiet/.
(5) Osterdahl M, Kocturk T, Koochek A, Wändell PE. Effects of a short-term intervention with a paleolithic diet in healthy volunteers. Eur J Clin Nutr. 2008;62(5):682-5.
(6) Lucas PW, Constantino PJ, Wood BA. Inferences regarding the diet of extinct hominins: structural and functional trends in dental and mandibular morphology within the hominin clade. J Anat. 2008;4(212):486-500.
(7) Eshed V, Gopher A, Hershkovitz I. Tooth wear and dental pathology at the advent of agriculture: new evidence from the Levant. Am J Phys Anthropol 2006;2(130):145-59.
(8) Lindeberg S, Jönsson T, Granfeldt Y, Borgstrand E, Soffman J, Sjöström K, Ahrén B. A Palaeolithic diet improves glucose tolerance more than a Mediterranean-like diet in individuals with ischaemic heart disease. Diabetologia 2007;9(50):1795-807.
(9) Elliott P, Walker LL, Little MP, Blair-West JR, Shade RE, Lee DR, et al. Change in salt intake affects blood pressure of chimpanzees: implications for human populations. Circulation 2007;14(116):1563-8.
(10) de Graaf C. Effects of snacks on energy intake: an evolutionary perspective. Appetite 2006;1(47):18-23.
(11) Amen-Ra N. Humans are evolutionarily adapted to caloric restriction resulting from ecologically dictated dietary deprivation imposed during the Plio-Pleistocene period. Med Hypotheses. 2006;5(66):978-84.
(12) Cordain L, Eaton SB, Miller JB, Mann N, Hill K. The paradoxical nature of hunter-gatherer diets: meat-based, yet non-atherogenic. Eur J Clin Nutr. 2002;56:42-52.

Why do Europeans, North Asians and Native Americans have pale skin?

2009-06-17T09:52:00.000-07:00

Skin colour is determined by the amount and type of the pigment melanin within it. This can be generated in small amounts by sun exposure but is nearly exclusively genetically influenced and therefore ancestry is the major contributor to the shade of an individual’s skin. Melanin in the skin absorbs and disperses 99.9% of UV in sunlight as heat. Without it, the UV radiation would generate direct and indirect damage to the DNA of living cells and the malfunction of their gene product, potentially damaging the health of the organism, namely through sunburn and skin cancer.

It is useful to consider the evolution of human pigmentation into the pale skinned populations of Europe, Asia and Native America as occurring in two stages: the first being from the pale pigments of apes and primates into the dark skinned early African humans and then paler again as humans migrated north, away from Africa. The early hairless humans evolved around 4.5 to 2 million years ago in the rain forests of Africa. They first became hairless to combat extreme heat through sweating and sweat evaporation. They moved out onto the East African savannah where they were exposed to much more sun and so more to the risks of UV exposure. This appears to be the first time a major selection pressure was imposed of the skin colour of the human race, although many different theories have been suggested as to the key selection pressure, initial thoughts were varied. One such was the risks of skin cancer and its development causing a selection pressure. However most skin cancers do not develop until later life (after many years of exposure) certainly after the age of child bearing and so would not reduce or remove the low melanin genes from the gene pool. Another suggestion was that sun burn to the nipple area prevented sufficient breast feeding for the young of low melanin individuals and thus their survival was less likely than high melanin individuals. However the greatest and most accepted selection pressure that resulted in the darkening skin of early humans is to do with sunlight’s affect on Folate levels. Very little sun exposure in pale skinned individuals can reduce Folate levels in the skin significantly. Folate has a large role in the development of foetal nervous system and bone marrow, and in sperm and red blood cell production. Pale skin, high sun exposure and therefore low Folate levels, decreases the fertility of males and developing embryos are less likely to reach full development; a huge selection pressure. The advantage of being dark skinned in Africa evolved quickly in early humans; and the trait is still seen today in African ancestries.

However, as well as being dangerous to our health, sunlight is also necessary for the production of Vitamin D in our skin. Vitamin D plays a vital role in the regulation and control of calcium and phosphate uptake and bone growth. Human skin cells have the ability to produce Vitamin D endogenously using energy from sunlight. In the diet of the early hunter-gather humans in Africa there was no need to allow sunlight into skin for the biosynthesis of vitamin D, as there was enough consumed from fish caught to maintain life processes. In fact it has been hypothesised that settlements in equatorial areas such as Africa could not have established without man’s ability to fish, and so maintain exogenous supplies of Vitamin D as skin evolved darker. This was also the reason early European settlers were able to survive until human skin pigmentation return to a paler shade around 6,000 to 12,000 years ago with dark skin, when man migrated north 40,000 years ago. It was only at this time, when farming arose as the main source of food, that levels of vitamin D consumed in the human diet decreased significantly. This presented a trade-off between reducing melanin in the skin allowing more sunlight and UV into the skin cells to produce Vitamin D, with the problems this presented in fertility and foetal development; a balancing act if you like. In Europe, where the average exposure to sun was much less than Africa, the paler skinned individuals of the population allowed more sunlight to penetrate the skin and therefore could internally produce more Vitamin D. This made them healthier, with stronger bones, and gave them a survival advantage over darker skinned individuals. The balance only swung in favour of paler skin here because the sunlight intensity was less than in more southerly areas and the ability to produce Vitamin D greatly outweighed the negative effects of reducing melanin in the skin. In fact, the further north the population was, the less sun exposure they experienced and the further the balance swung. In the far north there were nearly negligible risks of reduced Folate due to the lack of sunlight, and the biggest selection pressure was on those who could extract the most energy, from the little sunlight there was, for Vitamin D production; i.e. the paler in the population. This is reflected in modern European ancestry patterns of skin pigmentation. Celtic and Scandinavian population are very pale with low melanin as their environments had low sun exposure most of the time; whereas the lower European populations, such as the Spanish and Italians, where sun exposure is greater, have darker skin with more melanin enabling them to produce Vitamin D but also giving them greater protection against reduced Folate.

Northern Asians and Native Americans reside in a similar, or the same latitude, as Europeans (around 47O N) and their origins from the common early ancestors in Africa mean that the explanation for the pale colour of their skin is almost identical: the balance between using UV for Vitamin D production against the risks of reducing Folate. However, although pale compared to early humans and more southerly populations, Northern Asians and Native Americans are still darker than the people of Europe. One suggested reason for this has been that Asians and Native Americans consume more fish in their diets than Europeans. This is certainly the believed wisdom for the explanation of the dark skin of the Inuit population, who live at more northerly latitudes than almost all Europeans and yet have darker skin. The high fish diet appears to provide enough Vitamin D to compensate for the lesser UV sunlight without the need to evolve lighter skin. However, many Northern Asians and Native Americans settle in areas that are land locked and have very little fish in the diet, and vice versa many of the palest of the European population, for example Swedes and Danes, have very high fish consumption in their diet, yet have still evolved pale skin.

One suggested reason I found to be plausible is based on the central premise of sexual selection in mates. Research into mating preferences and perceptions of attractiveness pre-industrially has shown a “cross-cultural preference for lighter (skinned) women” (as concluded by van den Berge & Frost, 1986). Where man was capable of farming in the warmer climate of Sub-Saharan Africa, women were largely involved in the cultivation and production of food. This left men with more time and more capability to seek and provide for multiple wives, leading to a highly polygamous culture. This left few unmated individuals and very little preferential choice in mates which ultimately caused the unusual and unnecessarily dark pigment of Sub-Saharan Africans. When humans moved north into colder climes, the land supported less life and hunter-gatherers had to go further and in harsher conditions to get food. This meant that men had to work a lot harder to provide for multiple wives and many children, and for this reason European men became less-polygamous. The increased risks of travelling further in harsh conditions and the increased risk of running out of food also meant the male mortality rate was higher. These factors together increased the number of unmated men and women in the population and hence increased the choice available for preferential mating, which as previously discussed, was for paler women. In the majority of Europe, especially Scandinavia, Britain and North East Europe, the polar caps stretched further south 6000 years ago than today and the conditions for those living here were significantly harsher. This meant that particularly here, the choice in mating was much greater and the population became noticeably paler than in comparable latitudes. This is still evident in the extremely pale population of Celtic and Scandinavian ancestry.

The question still remains though; if the conditions are no longer this harsh in modern Europe, and probably haven’t been for a good few thousand years, why have these populations remained so pale, especially with such an obvious selection pressure as the risks to health of UV damage, such as sun burn and skin cancer?

Epithelioma (a type of skin cancer) prevalence correlates very well with latitude of settlement and therefore UV exposure, and also correlates well with areas of the body which are most exposed, for example the face and hands. The darker a person’s skin is naturally, the less chance they have that UV exposure will cause damage resulting in these epitheliomas. The reason this has not been experienced as a selection pressure may be the point I have already touched on: the average age of cancer onset is post child bearing age and so any pale skinned individuals that die due to UV induced cancers are likely to have already passed on their genetic material. In addition humans are unique in their ability to adapt not just by genetic mutation, but by cultural and social evolution, and it is my view that this is relevant to the pigmentation of these populations. For example humans clothe themselves and so reduce sun exposure to the skin by this method, removing the need to genetically evolve to reduce UV exposure. I feel this may contribute to a widely backed idea that populations reach an adaptive plateau, where they become well adapted enough to their habitat and environment that little further evolution occurs. For example, the early Scandinavians faced extreme challenges in their environment and so adapted very well to the harsh conditions, such as they’re paler skin. When the environment became less harsh they possessed characteristics that posed no disadvantage, and together with the human ability to culturally adapt to any further small changes in conditions, the requirements for them to evolve further were absent.

In conclusion, the evolution of pale skin in European, Northern Asian and Native Americans as humans migrated out of Africa was a result primarily of an evolutionary trade-off between the need for Vitamin D and prevention of the loss of Folate, and secondarily, the sexual preference and ability to choose mates that were of pale skin.

Why do Europeans, North Asians and Native Americans have pale skin?

2009-06-17T09:35:00.001-07:00

There is significant scientific evidence to suggest that Europeans, North Asians and North Americans are all descended from Africa. The Out Of Africa model suggests that homo sapiens arose in Africa and then migrated to other areas of the world to replace other hominid species such as homo erectus, and the Multiregional Continuity model suggests that hominid species that left Africa then evolved into homo sapiens all around the world. Whichever view is taken, it remains that homo sapiens descended from groups that lived in Africa. These groups almost certainly had dark skin to protect themselves from the strong tropical sun in Africa, and so there poses a question, why now do Europeans, North Asians and North Americans have pale skin, a clear differential from the dark skin of their ancestors.

There is one main hypothesis as to why this differentiation occurs. The basis of this answer lies within vitamin D. Vitamin D is needed for effective bone mineralisation and when it is deficient, bone softening diseases such as rickets and osteomalacia in adults occur, and possibly osteoporosis. These diseases cause the legs to be deformed, making walking harder. The thoracic cage also becomes deformed, causing more effort to be exerted in order to breathe. However, the most important problem with this disease in terms of evolution is pelvic deformations, where the pelvic bones collapse together, so childbirth and therefore reproduction is prevented from occurring. In countries more northern than Africa, the protective dark skin useful in Africa will not let enough of the weaker sun in, and so deficiencies could occur. The gene for skin colour has been identified in Europeans and Africans as SLC24A5, with one allele being present in 98% Europeans and the other allele being present in most Africans and East Asians. The gene for skin colour in North Asians is still being investigated.

Recent evidence has uncovered that in fact human skin stayed dark for 30 000 years after the migration out of Africa, when it was originally thought light skin occurred when they first moved. Therefore, this theory about vitamin D is flawed. There are theories as to why there was such a long gap. One of them is that at first humans were hunter-gatherers, herders and fishers, and so their diet included enough vitamin D not to cause any problems. However, at around the same time as the skin colour change occurred, farming became a new way of life and expanded, which did not provide enough vitamin D in the diet. Farming allowed for much larger population sizes to live together, and because mutations are rare, larger populations give a higher chance of a mutation occurring, and that that mutation is actually useful. A mutation is also more likely to occur in one of these populations because they are living in a challenging environment (not enough UV) that causes selection pressures. These new challenging environments and a growing population cause accelerated human evolution, and in this example it would be a lightening of skin colour. Another factor in this could be cultural for example heavier clothing being worn, and so decreased the area available for absorption of UV.

There are other theories however, as many people think that pale skin is not an advantage in most environments in the higher latitudes, due to the vulnerability to sunburn and malignant melanomas, and so do not think that pale skin evolved due to natural selection. The two presented here are sexual selection and parental selection.

Another theory about how lighter skin has come about is that there has been a common selective force that acted on three characteristics – skin, hair and eye colour - in the northern latitudes. This force has been suggested to be sexual selection, and could have acted on an existing sexual dimorphism of men generally being browner and women being fairer. The selection is seen in all upper classes around the world of having a preference for fairer skinned females to marry. Because of this, upper class men may choose lighter females and so over generations the class lightens. Some believe that this sexual selection for light skin counteracts natural selection for dark skin. The difference in skin colour geographically may be due to a balance between natural and sexual selection, so suggesting that it is a combination of both factors. This balance differs according to the latitude, so at low latitudes dark skin is prevalent as natural selection overrides the male preference for light skin. But at higher latitudes where natural selection ceases to act, sexual selection becomes more important, and causes light-skinned populations with the females lighter than the males.

Another factor that is argued by Judith Harris is parental selection, mainly maternal selection. In many cultures a form of birth control was infanticide, where the child was killed after birth. The most recent example of a culture in which this takes place is the !Kung. This way of living gave mothers the power to exert an influence on evolution by deciding to keep or abandon a new born. A decision may be made before birth to abandon the child due to bad timing as the previous child may not have been weaned, or food was scarce, or there was no partner to provide for the baby. However, once the baby is born, this decision may be overturned depending on the reaction to the newborn itself. The newborn may have been sickly, weak, the wrong sex, or have a congenital malformation. However the decision may go the other way if the baby is especially beautiful, conforming to the mother’s standards of beauty. Although this decision may only be made in a small percentage, this all adds up and Harris argues that it is big enough to exert an influence on the characteristics of our species. Harris proposes that hairlessness and pale skin colour seen in northern countries is partly the result of parental selection. She accepts that sexual selection also played a part but that it was parental selection that speeded the evolutionary process up, producing very noticeable changes in a relatively short space of time. She combines the concept of hairlessness and pale skinned because a hairless pale human would be very exposed to the dangers of the sun, and so she believes there must be some other reason why so much of the world’s population is not adapted as best as it can to the environment. The concept of beauty that may sway a mother to keep her baby is of a pale skinned baby. This may be linked to sexual selection, as parents would want a pale skinned daughter so that she can have more choice of husband, and so passing on desirable characteristics that the parents will have as grandchildren.

It appears that there is a difference in opinion regarding how pale skin came about. Unfortunately, evidence to prove either theory is hard if not impossible to come by, and so there is a possibility we will never know. However, in my opinion, I believe that it could be a combination of all three, but with the main influencing factor being natural selection. This is because i don’t believe that such a huge change could come across just through sexual or parental selection alone. Along with this, there is not concrete evidence to support the sexual selection claim and one study has shown that there is no evidence for a correlation between increasing distance from the equator and increased sexual dimorphism.

References:
Skin colour evolution in Europeans and social skin colour vs disease in Puerto Ricans, Dienekes Anthropology Blog
Sexual selection as a cause of human skin colour variation: Darwin's hypothesis revisited by Aoki K, Pubmed.
Human skin colour dimorphism, Kelly and Madrigal, Department of Anthropology, University of South Florida
Judith Harris, Parental Selection: A Third Selection Process in the Evolution of Human Hairlessness and Skin Color

Why do Europeans, North Asians and Native Americans have pale skins?

2009-06-17T09:32:00.000-07:00

The first hominid species, Homo habilis, is believed to have evolved around 2 million years ago in East Africa, The modern human, Homo sapiens, is believed to have evolved from an earlier hominid species, Homo erectus, and quickly colonized much of the African continent. As Homo sapiens emerged, groups of individuals spread slowly around 60,000 years ago to other geographically close by regions through what can be described as the Out of Africa hypothesis. Different tribes adapted to their new habitats through evolutionary changes. Most notable appearance-wise is skin colour, which is at its darkest in individuals living at the equator and palest in those living nearest to the poles. Even if humans did evolve, as suggested by Milford Wolpoff and his associates in their Multiregional hypothesis, separately and independently, the same evolutionary mutations would hold true as to the reasoning behind varying skin colouration. Pigmentation arises because of melanin, a pigment that comes in two types: pheomelanin (red, and found predominantly in freckles and reddened areas such as the lips) and eumelanin (very dark brown). Both the amount and type are determined by four to six genes which operate under incomplete dominance. One copy of each of those genes is inherited from each parent. Each gene comes in several alleles, resulting in the great variety of different skin tones. So what purpose does this pigmentation serve?

Unlike us, many of our hairier mammalian cousins do not have such a pigmented skin; by having a hairy coat, they are protected from UV radiation-induced damage as the hairs themselves absorb or reflect most-short wavelength solar radiation. Non-human mammals that are active in hotter, sunnier climates tend to be sparsely coated in order to facilitate passive heat loss (and sweating is limited to certain areas). Unsurprisingly, they tend to show increased melanin concentrations in the skin along their backs where they are exposed to more sunlight. Our primate ancestors would also have had thick hair and hence pale skin.

Early hominids in Africa were active hunters and gatherers and as such, it was an evolutionary advantage to have less hair and more exocrine glands for increased sweat production, allowing early man to pursue prey and be active in the sun for longer without overheating. Having virtually naked skin, it was imperative that hair loss had to be coupled with increasing melanin production in order to protect underlying skin cells from the effects of over-exposure to UV radiation (which can cause mutation in underlying cells and hence lead to melanomas and cancer) by absorbing and dispersing it as infrared radiation (felt as heat).

A widely accepted hypothesis regarding variations in pigmentation is that of Vitamin D Biosynthesis. It is known that sunlight, particularly ultraviolet rays, stimulate the production of vitamin D, which is partly responsible for calcium uptake in bones. A deficiency of vitamin D can lead to once-common conditions such as rickets, in which bones do not form properly and become misshapen. Heavily pigmented skin in areas of high sunlight exposure not only provides excellent protection from UV radiation, but can also limit vitamin D biosynthesis and hence reduce the risk of developing toxicity. Too much vitamin D can lead to hypercalcaemia followed by nausea, vomiting, weakness, polyuria and polydipsia.

UV exposure decreases the further south or north one travels from the equator due to sunlight having to travel through more ozone and atmospheric gases (because of the tilt of the Earth's axis) and hence, an individual with heavily pigmented skin would struggle to produce enough vitamin D. Such conditions would favour slightly paler skin as adequate protection from sunlight is achieved, whilst maintaining favourable levels of vitamin D₃ synthesis. The first European settlers would have been quite dark in complexion, and with a considerably lower exposure level of UV radiation, vitamin D synthesis was impeded. An American study carried out by the the United States Department of Agriculture found “87% of African Americans to be Vitamin D deficient”. To address this issue, some countries (particularly Canada and the USA) have programmes to ensure fortification of milk with vitamin D.

Also contributing to evolutionary adaptations of skin colour is the folate hypothesis. This suggests that folate (or folic acid), which is vital for the synthesis, repair and expression of DNA. It is also essential in red blood cell and sperm production (and as such its presence is quite necessary for human reproduction) Darker skin helps protect folate from UV-induced photolysis and hence helps maintain adequate stores of it. Darker skin however would be of no greater advantage in less sun-intense climates because vitamin D production would be more of a priority and hence, paler skin prevailed.

Interestingly, it has been observed that females tend to exhibit lighter skin pigmentation than males in all populations, and that sexual selection is partly responsible for a reduction in pigmentation in expanding populations. This hypothesis is based on observations that the attraction of human females and human males is partially due to their lighter pigmentation. Thus, lighter-coloured females are perceived to be more feminine than their darker counterparts and therefore would be preferred partners. This idea was further advanced in that paler females would have higher vitamin D production and would be able to meet the calcium demands of pregnancy and lactation. Due to maternal chromosomes, further generations would in theory become gradually paler. This can still be seen today in many Asian countries, particularly in the Far East where it is more desirable for women to be paler. This tends to be for cultural reasons, rather than to bring about any advantageous characteristics in children; for example, in China, having a tan is linked to historically working in fields and being a peasant- having a lighter complexion reflects a higher social status rather than any indication of undesirable genetics and many women practice diligent sun avoidance and take up chemical skin-lightening .

Early migrants to Europe would still have had fairly dark skin, and nowhere near as light as today's modern northern Europeans. However as mentioned, there would have been less exposure to the sun and this would have led to even lower production rates of vitamin D and lighter skin would've proven more favourable. Given that increased vitamin D would give individuals stronger skeletons as well as serving a function in pregnancy, it would have allowed modern man to quickly establish stable and expanding colonies. A superior intellect combined with technologically greater tools and weaponry would have given Homo sapiens a considerable advantage over already present populations of Homo neanderthalis. These factors may have led to the retreat of many neanderthal tribes to the southern tip of Europe (and their eventual extinction). Homo sapiens would prove the victorious conqueror in Europe.

Tribes still exist and have done so (although in considerably smaller numbers ) in the colder regions of Northern Asia, for example in Siberia, for thousands of years after travelling (according to the Out of Africa hypothesis) north east from the middle and near East. Like Europeans, they are also of pale skin because of reduced sunlight exposure. However, populations living nearer to the Siberian Arctic, as well as many other Inuit tribes may be of a darker, more South-East Asian complexion as they gain enough vitamin D from their fishy diet and biosynthesis becomes less important. More melanin in the skin may also serve to prevent over production (even though sunlight is of a lower intensity).

Native Americans share certain phenotype characteristics with the indigenous peoples of North Asia, because it is believed the same people traversed huge ice plains thousands of years ago and colonised North America and consequently South America. Interestingly, many native American tribe populations cannot grow or grow very little facial hair, although whether this provides an evolutionary advantage remains to be seen- it may be through sexual selection, females preferred males with less facial hair and so such genes were gradually removed from the population.

To conclude, inhabitants of Europe, North America and North Asia are genetically paler than their African ancestors who spread and conquered new lands, as an evolutionary response to differing amounts of sunlight (or more precisely UV radiation). Melanin serves to protect underlying cells from the harmful effects of UV. Dark skin provides the best protection from UV-induced cancers and folate photolysis, but leads to reduced vitamin D production. The opposite is true in pale skin. In real world terms, there is essentially a trade off between each factor and an optimum level of melanin concentration is achieved based on basically how strong the sun is. Given today's chemical and technolgical advances, although we can choose to make our skin lighter or darker to appease a personal preference or reflect our socioeconomic status, we were all born a certain colour because of the actions of our ancestors and how they evolved to enable them to prevail wherever they chose to settle.

References: The Evolution of Human Skin and Skin Color - Nina G Jablonski

How can we explain the course of the recurrent laryngeal nerve?

2009-06-17T08:43:00.000-07:00

First of all it is essential that the actual use and course taken by this nerve is outlined.

The recurrent laryngeal nerve is just one of many branches of the vagus nerve, the 10^th cranial nerve. This particular branch is important, as it is the sole supplier of motor and sensory innervation to the larynx, commonly referred to as the voice box. The co-ordination of these muscles allows many animals to produce a wide range of sounds. This ability is indispensable in some species, such as humans who use their voice box to produce sounds in the form of words in order to communicate. Communication is an essential asset. Those animals that in the past had this ability had a distinct advantage over those who could not communicate. It provides protect when hunted and stealth when hunting.

In humans and mammals, the recurrent laryngeal nerves take a rather absurd route. As I have already stated, the target of the nerves is the larynx which is located anteriorly in the neck. The nerves originate in the brainstem, specifically the medulla oblongata, which is a portion of the central nervous system between the brain and the spinal cord. The nerves leave the medulla whilst still in the neurocranium (skull), but quickly exit via the right and left jugular foramen. After leaving the skull, the nerves descend down the neck, one on each side, and into the thorax, before looping back on themselves and into the neck once again before reaching their final destination. The route is slightly different on both sides of the body. On the right side, the nerve loops under the right subclavian artery before its ascent to the larynx whereas the left recurrent laryngeal nerve loops beneath the aorta.

Although this route seems to be strange in humans, the extremity of this illogical route is epitomised in a giraffe. The indirect route means that at least six extra feet of nerve is required when compared to a direct alternative. Personally, this seems tremendously inappropriate, as it is an extreme waste of resources, and also poses a larger potential for damage especially for the left recurrent laryngeal nerve, as not only can problems in the neck cause nerve damage but also problems in the left side of the thorax. For example, a tumour in the left lung could cause compression on the left recurrent laryngeal nerve leading to paralysis of the muscles on the left side of the larynx, possibly resulting in a decrease in the ability to communicate and the subsequent loss of an evolutionary advantage.

Consequently, I believe that it is fair to state that this situation lacks an intelligent design, as there is obviously a much more ideal design that would not waste resources or pose an increased risk of problems occurring. If a mere mortal such as myself can easily outline the flaws of this situation, it is acceptable to assume that no omniscient, creator would have designed the recurrent laryngeal nerve as it stands today. Therefore, I shall now look to see if Charles Darwin’s work can help answer my query and provide the reasoning beyond this strange phenomenon.

The presence of this nerve can be traced back down the branching tree of life to fish-like vertebrates, which appear to share the presence of a similar nerve. However, the nerve in fish does not have the same route, and therefore does not share the same name but is still the fourth branch of the vagus nerve.

Instead, the nerve in fish-like vertebrates travels straight to its target, which is the 6^th gill as it appears to follow the route of the 6^th arterial arch. This same general principle, of the nerve following the arterial branch, is also shown in mammals and humans.

During evolution, some fish-like vertebrates appear to have migrated onto land and evolved into land creatures. This was only recently proven by evidence in the fossil record. Before the discovery of a certain fossil, it was only assumed that some of the water living animals evolved into land living creatures, but since the first report in 2006 of the Tiktaalik roseae, evolutionists believe that they have found the missing link; the bridge between aquatic life in the oceans to life on land. These fish-like vertebrates are our ancestors.

This statement is further confirmed by the fact that humans and mammals follow a similar developmental principle as their fish-like ancestors, as during the embryological development of land animals gill like remnants can be seen. However, during the evolutionary step from fish to land animals, the gills of the fish disappeared in the adult form of land animals.

The pharyngeal arches, located on an embryos neck appear extremely like the gills of a fish. However, their function is no longer to supply oxygen by becoming gills as they did in previous aquatic species, but they are now responsible for giving rise to the development of internal bodily structures.

As already stated, we have a particular interest in the 6^th arch. In both fish and humans, this arch gives rise to the 6^th arterial arch. However, the location which this arch migrates to is different. In fish, the arch runs next to the 6^th gill and therefore this means the following nerve has a direct route to its target.

However, in humans, the 6^th arterial arch gives rise to the right and left pulmonary arteries and the ductus arteriosus which are vessels located around the heart. Hence the nerve follows this path and ends up travelling from the brainstem into the thorax. However, the 6^th pharyngeal arch also contributes to the formation of the larynx, including its cartilaginous skeleton and its intrinsic musculature. Therefore, the nerve then takes a detour from its position in the thorax, after the development of the arterial system is complete, back up to its target in the neck to help in the formation of the larynx.

The answer to why this happens in this particular order is all hidden in the past. Once a species develops, the developmental process cannot be undone as there are essential elements that must be maintained in order for an organism to survive i.e. the development of the arterial system. This is often portrayed in words as ‘the knot evolution cannot untangle.’ The need for some developmental elements to be maintained, places evolutionary constraints upon future species that are to evolve. This is evoked strongly in this example.

The constraint of the development of the arterial system means that the fourth branch of the vagus nerve has to follow the migration of the 6^th arterial arch first as this is a fundamental step in the development of an organism. This cornerstone means that any evolutionary advances have to occur after this step has taken place. Therefore, when the larynx evolved, the laryngeal nerve had to evolve too, but in accordance with the constraints put upon it. It therefore had to travel from the thorax to the larynx, and as a result became known as the recurrent laryngeal nerve due to its reoccurring route through the neck.

I believe I have revealed that this nerves route is an example of unintelligent design and that its route can be explained clearly and precisely through the work of Charles Darwin and the process of evolution, that can only move forwards, resulting in some weird and absurd but often wonderful creations.

Sources:

The Rough Guide to Evolution – Mark Pollen

http://www.sciencedaily.com/releases/2008/10/081015144123.htm

Evolution – Mark Ridley

Evolution - Monroe W. Strickberger

Clinically Orientated Anatomy – Keith Moore and Arthur Daley

Tay-Sachs disease in Ashkenazi Jews: Origins and Preventions

2009-06-17T06:42:00.001-07:00

Tay-Sachs disease is an autosomal recessive disease which is fatal in its most common form, known as infantile Tay-Sachs. It is known to have a high prevalence in Ashkenazi Jews. In this essay I am going to explain how the high prevalence of the mutation could have originated in the Jewish population and how the disease can be prevented.

Approximately 1 in 25 Ashkenazi Jews are carriers of Tay-Sachs disease which makes this population particularly susceptible. Only 1 in 250 people are carriers in the general population. Although Ashkenazi Jews are more susceptible to many other diseases Tay-Sachs is a particularly terrible disease as it leaves a child blind, deaf and unable to swallow. Babies with Tay-Sachs are born without Hexosaminidase A which would otherwise clear out unwanted fatty proteins which interfere with baby’s sight, hearing, movement and mental development.

It is not known for definite as to why this population has a high carrier rate but there are some very strong explanations. The first theory I found involves the infectious disease tuberculosis. From some evidence it appears that Tay-Sachs provides some protection against TB, and it is this that may explain why Ashkenazi Jews have a high carrier rate. When World War 2 broke out TB spread through the eastern European Jewish settlements. This was particularly dangerous because these Jews were prevented from moving out of the ghettos that they were forced to live in by the Nazis. However, healthy parents who had children with Tay-Sachs disease did not contact TB, even though they were sometimes repeatedly exposed. The parents must have been carriers of Tay-Sachs in order to have children with the disease, since it is an autosomal recessive infliction. Therefore being a carrier of Tay-Sachs seems to have provided some sort of protection against TB, although why it provides protection is not so clear and is still not fully known.

To relate this idea to evolution, the Ashkenazi Jews at the time were exposed to a serious epidemic of TB in their area, so many people who were not carriers would have contacted TB and died meaning they would not raise offspring in the future. On the other hand individuals with the allele for Tay-Sachs would not have contacted TB and passed on their genes to their offspring. It is an example of survival of the fittest (natural selection) so even though Tay-Sachs is a dangerous disease, at the time of world war 2 many people without the allele for the disease were wiped out by TB making the allele more prevalent in the population.

Genetic drift is another theory as to why Ashkenazi Jews have a higher carrier frequency of Tay-Sachs. Genetic drift is the random fluctuations of frequencies of the appearance of genes in an isolated population. It relies on the fact that alleles of offspring are a random sample of those of their parents, and one allele can become more prevalent in a population by chance. As I have already described the Ashkenazi Jews were isolated in ghettos by the Nazis which is why they were susceptible to genetic drift. The effect of genetic drift is much larger in smaller populations which is why it doesn’t usually play a large role in allele frequency for the general population. Using this theory, it is possible the Tay-Sachs is prevalent in Ashkenazi Jews just through a random process. The fact that there was a small population involved meant that it was easier for one allele to become more prevalent than another allele. Genetic drift would have also played a role in making the prevalence of the Tay-Sachs allele high in the population even if the Ashkenazi Jews were not forced to stay in ghettoes. This is because the population of Ashkenazi Jews was small in the first place, and a small population would allow genetic drift to be more effective. Natural selection would not have caused the allele to become prevalent without the effect of TB because natural selection only allows alleles giving an advantage to be passed on to offspring, which is why genetic drift is a strong theory.

The last theory is the founder effect which occurs when a population is started from a very small number of individuals. It believed the Ashkenazi Jew population was started from only a few thousand individuals who lived in Eastern Europe, and millions of people can now trace their ancestry to this population. Therefore even if a small number of people in the founding population are carriers of the mutation, the defect would become amplified over time and so when the population reaches high numbers, there will be a large number of people with the defect. This theory would need to rely on the chance presence of certain mutations in the founders of today’s Ashkenazi Jewish population.

At the moment there is no cure for Tay-Sachs disease. We can only try and prevent more cases from occurring, and this is done through screening for potential carriers of the disease. This is especially important if the future parents have both high risk ethnic origins such as both being Ashkenazi Jews. The potential parents both have genetic tests done to see if they are carriers or not, so they can be warned about the dangers of starting a family. Genetic tests of the amniotic fluid in the womb can be done to diagnose Tay-Sachs, so the parents can chose whether to terminate the pregnancy. These tests used to take a long time to show results so they were not so effective in the past. However now they can be done with a simple blood test with results being shown in under 48 hours. The blood samples can be analyzed by enzyme assay or DNA studies. Some Jewish communities have organised pre-marital counselling to help reduce the occurrence of the disease. These methods can reduce the amount of children being born with Tay-Sachs.

In conclusion I cannot decide which theory is the most likely to have caused the high prevalence of Tay-Sachs in Ashkenazi Jews as they are all valid explanations. Even though genetic drift and the founder effect are two different theories, both may have contributed to the high prevalence while the TB epidemic the Jews faced only increased the proportion of carriers in the population. So it is likely that all three theories played a part in keeping the mutation high in Ashkenazi Jews. Regarding the future of the population, it is vital to advertise genetic testing more to the populations at risk as the methods used seem to have been successful in reducing the numbers of children with Tay-Sachs.

Human Genetics: Concepts and Applications (Second edition, 1997) pp. 247-248 by Ricki Lewis

http://www.nhs.uk/Conditions/Tay-Sachs-disease/Pages/Prevention.aspx

http://www.genome.gov/10001220

http://judaism.about.com/od/health/a/geneticdisorder.htm

2009-06-17T06:06:00.000-07:00

Darwin and slavery

Sam Pearson

“I thank God, I shall never again visit a slave country. To this day, if I hear a distant scream, it recalls with painful vividness my feelings, when passing a house near Pernamabuco, I heard the most pitiful moans, and could not but suspect that some poor slave was being tortured, yet knew that I was as powerless as a child even to remonstrate”.

This is a direct quotation from Darwin outlining one of the times he experienced the maltreatment of slaves during his travels in south America as a small child. He writes later in life how he lived across the street from a women in Rio de janeiro who regularly tortured her slaves and these experiences seem to have shaped the views that Darwin would have on the matter for the rest of his life.

Indeed Darwin came from a family who had worked towards the abolition of slavery as both his grandfathers where keen abolitionists. His dads father Jos Wedgewood is indeed said to be the person who created the famous picture of a slave on his knees asking his master if he were not his brother. His grandfather even sold the wedgewood showroom in London and put the proceeds into the antislave movement in particular the work of Thomas Clarkson who traveled around collecting statistics on slavery. With such strong family beliefs on slaver it seems impossible that the topic would not affect Darwins life.

It has been written before that Darwin created his theory of common descent from black africans as support to his cause of abolishing slavery. It is true that there are many instances before Darwin published this theory of him stating his hatred of slavery and it seems plausible that he would have doctored his results in order prove that we shared a common ancestory and to prove to the ruling classes that they were no better than the slaves that they emprisoned. However if you look at the evidence that Darwin collected on the matter his quote in the descent of man “it is … probable that our early progenitors lived in the African continent” seems far less biased and far more scientifically viable indeed even to this day the case that we all descended from Africans gets stronger and stronger. Indeed the place were the human race evolved is believed to have been found and human fossils 40,000 years older than anywhere else in the world have been found in Africa.

So how did Darwin’s work undermine the slave trade? It is important to note that at the time of Darwin’s writing the british empire had abolished slavery and policed its waters in an effort to reduce the trade of other countries. Darwin’s main targets were therefore the slave traders of north and south America. At the time many plantation and factory owners in America saw those of black descent as a completely different species to that of the European descended white man. They therefore saw no moral problem with enslaving this so called inferior race. Darwin’s work showed that in fact white man had descended from black Africans. This undermined the ideals of the enslavers who proposed that all none Caucasian people had descended separately and therefore could be treated differently and although it may not have directly affected the slave trade it certainly would have altered the beliefs of those who believed in Darwin’s work. It also provided scientific evidence to aid the antislave movement. Although Darwin omitted human evolution from the origin of species saying “the subject was so surrounded with prejudices” it was well known amongst the science community that human evolution was at its heart and indeed Darwin published his views on human descent in later works.

Indeed Darwin devoted 35 pages in the descent of man to ‘on the races of man’ a chapter where he outlines that the differences between different races are actually very small in the grand scheme of nature and that the physical differences are not caused by natural selection ie there are not different evolutionary pathways for all races. Instead Darwin wrote that these differences are actually caused by sexual selection whereby males compete for females and certain characteristics are desireable in different subgroups. This theory therefore proposed that the black population was equal to the white population and that the minor differences between them were definitely not due to differences in evolution.

At the time Darwin’s name was slightly tainted by subtheories of his work namely social Darwinism as proposed by Herbert spencer. Darwin had stated that sympathetic behaviour towards other humans was an important part of natural selection but he rejected the work of Spencer.

On the beagles return voyage three uneducated islanders traveled with Darwin and the crew. Although the cultural differences between the two groups where enormous Darwin noticed that they shared many mannerisms and that there were indeed many similarities between the two groups. It has been suggested that this was one of the triggers for Darwin’s brainwave that all humans descended from a common ancestor.

In conclusion Darwin’s family background and upbringing were extremely important in his beliefs on the atrocities of slavery and without these his groundbreaking work on mans common ancestor that helped undermine the racist slave traders may never have come to the fore and one of the great scientific works may never have come into being.

Sources:

Darwins twin track, Adrian Desmond

Massachusetts Darwin 2009 bicentennial project, Johnathan King

Darwin’s Evolution Theory, Inspired By Abolition of Slavery? David Fierce

Purpose of this blog: June 2009

2009-06-15T03:14:00.000-07:00

This blog was created by Professor Mark Pallen for the purpose of allowing medical students to blog on selected topics during a one-week student-selected activity. For the June 2009 SSA, students who choose to blog, should post their work (1000-2000 words) by 7pm on Wednesday 17th June 2009.

Evolutionary Trade-Offs:Sickle Cell Disease and Malaria

2009-02-19T11:04:00.000-08:00

Evolutionary trade-offs in performance from one environment to another have long been thought to be essential in the balance in population and distribution of organisms. It is an essential concept in natural selection. (The process in nature by which, according to Darwin's theory of evolution, only the organisms best adapted to their environment tend to survive and transmit their genetic characteristics in increasing numbers to succeeding generations while those less adapted tend to be eliminated.) An advantageous mutation in a certain environment will increase the likelihood of reaching the age of reproduction, allowing passing on of the gene to the next generation, therefore a positive mutation. If the mutation is detrimental to health and the person dies before reproduction, the mutation is lost and is therefore a negative mutation. Natural selection has to be considered in the context of "pre-modern" societies. Modern medicine has altered the balance of nature and often allows us to rescue people who otherwise would die of their condition, for example, juvenile diabetes; a hereditary disease which used to cause death in childhood. Now due to medical advances it is now possible to treat juvenile diabetes therefore natural selection is no longer a problem. Other than modern medicine, natural selection would suggest that no hereditary disease would be passed on to the next generation. This is in fact not true, this is when evolutionary trade-offs occur, where pros and cons exist for a mutated gene, providing enough advantage to pass on the gene to the next generation.
One evolutionary trade-off which has caused much interest in the medical world of late is the genetic trade-off evolving amongst people who carry genes for sickle cell disease, and the protection they have from malaria.
Malaria is one of the most common infectious diseases, each year, attacking 400 million, in which 3 million develop the illness. The disease is caused by transmission of plasmodium parasite usually by being bitten by an infective female Anopheles mosquito. Only four types of the plasmodium can infect humans, the most dangerous being P.falciparum (the other three being P.vivax, P.ovale, P.malariae).
The plasmodium parasite spends part of its life in the mosquito and part in the human host. The infective plasmodial sporozoites enter the bloodstream from the saliva of the feeding female anopheles mosquito. The Kupfer cells which are part of the reticulo-endothelial system in the liver clear the sporozoites from the blood stream and kill many of the organisms. A fraction of the sporozoites escape destruction however, and penetrate the hepatocytes of the liver where they multiply. The parasite once in the hepatocyte transform into a new entity; schitzonts which replicate vigorously forming merozites which totally fill the hepatocytes. Rupture of the hepatocyte membrane causes a release of merozoites into the bloodstream where they invade circulating erythrocytes where they assume a ring form called trophozoites. These organisms consume haemoglobin, enlarge and metamorph into schizonts and merozoites. Eventually the erythrocytes lyse and release merozoites that can penetrate new erythrocytes. Trophozoites can also form gametocytes in the erythrocytes which is the sexual form of the parasite which stay in the red cell. Transmission of the parasite into a feeding mosquito occurs when these gametocytes are taken in. The sexual reproduction cycle then begins in the mosquito, which subsequently leads to human transmission.
There are many points in the life cycle where the parasite could be targeted for destruction. Firstly the antibodies and lymphocytes called ‘natural killer cells’ attacking the sporozites when first injected into the blood stream. Prior exposure to the parasite would cause a stronger more effective immune attack due to conditioned lymphocytes. Another point is the intrahepatic phase of malaria. Potentially a mutation to the structure and function of hepatic cells that could kill the parasite or slow its growth would prove effective, although none is known. The last phase of the parasite’s life cycle that the body could attack is at the red cell invasion and multiplication phase; where a mutation could destroy infected cells and parasites allowing replacement by non-infected red blood cells which would potentially eliminate the malaria parasite. At this phase the mutated sickle haemoglobin (haemoglobin S) proves effective in impairing malaria growth and development when it is in its heterozygous state.
Sickle cell trait provides a survival advantage over people with normal haemoglobin in regions where malaria is endemic for example in West Africa. The first signs of the relationship between carriers of the mutant hemoglobin S and their protection against malaria, was determined due to the realization that the geographical distribution of the gene for haemoglobin S and the distribution of malaria in Africa virtually overlap. Sickle haemoglobin provides the best example of a change in the haemoglobin molecule that impairs malaria growth and development.
The mechanism in which it does this is unsure, but there are many circulating ideas.
In 1970 it was suggested by Luzzatto, et al that it was due to low oxygen tensions causing cells with the haemoglobin S to sickle. When the erythrocyte is then infected by the parasite P.falciparum it deforms due to its high metabolic rate therefore reducing the oxygen tension within the erythrocytes. Deformation of sickle trait erythrocytes would mark these cells as abnormal and then be removed from the circulation and then destroyed in the reticuloendothelial system by macrophages.
Others suggest that malaria parasite could be damaged or killed directly in sickle trait erythrocytes impairing on its proliferation. Ultrastructural studies showed extensive vacuole formation in P. falciparum parasites inhabiting sickle trait red cells that were incubated at low oxygen tension, suggesting metabolic damage to the parasites (Friedman, 1979).
Other investigations suggest that oxygen radical formation in sickle trait erythrocytes retards growth and even kills the P. falciparum parasite (Anastasi, 1984). Sickle trait red cells produce higher levels of the superoxide anion (O2-) and hydrogen peroxide (H2O2) than do normal erythrocytes. Each compound is toxic to a number of pathogens, including malarial parasites.
Sickle cell disease in its homozygous form can prove fatal, and it is likely that a person suffering will not reach the age of reproduction, therefore the genes will not be passed on, and its advantage in protection against malaria will not be seen. This means that negative selection exists for sickle cell disease. However it takes two copies of the mutant gene, to give someone the full-blown disease. Heterozygote carrying one mutant allele and another normal (sickle cell trait) will see a heterozygous advantage, because of the protection against malaria. This advantage is known as a balanced polymorphism where the heterozygote for two alleles of a gene has an advantage over either of the homozygous forms. However this does allow transmission of the mutant gene. Two heterozygote states for the allele mating would introduce a possibility to reproduce an offspring with the disease. The survival rates of the heterozygote state will be greater than the homozygote form, therefore increasing the chances of an affected offspring.
Increasing knowledge in evolutionary trade-offs that occur in pathogens have been used as the basis of new medical treatments. One example of an evolutionary trade-off that is the basis of a form of treatment for the disease is HIV. Human immunodeficiency virus is one of the fastest evolving entities known, making it very difficult to treat. Resistant strains of the HIV evolve when exposed to antiretroviral drugs, due to accumulating lots of mutations during reproduction. However, gaining the advantage of growing resistance to antiretroviral drugs, does come with its negative effects. If you place a resistant and non-resistant organism in head-to-head competition in the absence of the pesticide or drug, the non-resistant organisms generally wins. This theory is the basis of a new dosage regime for the drug.
If a patient has developed a resistant strand of virus to a drug, then the patient stops taking the drug, evolution theory suggests that the viral load will evolve back to a non-resistant strain due to natural selection. If the patient then takes a very strong dose of the same drug, it could effectively retard the replication of those non-resistant viruses, reducing the viral load to very low levels.
This therapy has shown early, promising results, although its efficacy is low and it may not eliminate HIV, but it could slow down the progression of the disease. The treatment however has laid a grounding for more research, and proves that we can impinge on these evolutionary trade-offs and take advantage of them in medical treatment.

The Evolution of Lactose Tolerance

2009-02-19T08:54:00.000-08:00

In the world today, the majority of adults are lactose intolerant. In certain populations, however, the exact opposite is true. In this essay I will consider the evolutionary explanation for this.

At birth, all humans produce the enzyme lactase. Lactase hydrolyses the disaccharide lactose into galactose and glucose monosaccharides. In humans, lactase is present mainly along the brush border membrane of the enterocytes lining the villi of the small intestine. It is essential for digestive hydrolysis of lactose in milk, as lactose itself cannot be directly absorbed into the bloodstream at any point along the gastro-intestinal tract. In non dairy consuming societies, lactase production usually drops about 90% during the first four years of life (after the weaning phase is over), although the length of this period varies between individuals. This is due to the ‘switching off’ of the lactase gene. This used to be true of the human race in general, but in dairy consuming areas, a mutation in the gene regulating the ‘switching off’ of lactase production, situated on chromosome 2, has now become very common. Such a mutation is known to have arisen among an early cattle-raising people, the Funnel Beaker culture, who lived in north-central Europe around 5,000 to 6,000 years ago. This lactase-persistence allele is found in more than 90 per cent of Danes and Swedes, and 50 per cent of Spanish and French – illustrating that the mutation becomes progressively less common in Europeans who live at increasing distances from the ancient Funnel Beaker region. The mutation is rare in non-pastoral communities such as the Chinese (only 1 per cent of the population have it). In pastoral areas in East Africa, there is a very low frequency of this allele, although many adults are lactose tolerant. An international team of researchers has found that lactose tolerance in East African adults is served by three newly discovered variants of the lactase gene, all of which are independent of each other and the European strain. As in the European allele the mutation is present in the control region of the gene. These African variants appear to have arisen several thousand years later than the European allele. This fits well with archaeological evidence showing that pastoral farming groups from the north reached northern Kenya around 4,500 years ago, and southern Kenya and Tanzania about 3,300 years ago. In both Europe and Africa, the mutations have arisen after a long period of sustained pastoral lifestyle. The mutations have simply developed differently in the two different areas.

There was at first much debate as to whether the consuming of dairy produce caused the increased frequency of the lactase-persistence allele – called the culture-historical hypothesis – or if in fact that a dairy diet was introduced after the mutation became more common – the reverse cause hypothesis – (very much a chicken/egg deliberation). An analysis of DNA samples taken from skeletons of early European farmers shows that the lactase persistence allele was not present, thus supporting the culture-historical hypothesis. This means that an increase in dairy farming caused the prevalence of the lactase-persistence allele to gradually increase over the generations. This also means that the current high prevalence of the allele must be due to natural selection. In ‘The Origin of Species’, Darwin explains natural selection thus: ‘Owing to this struggle to life, any variation, however slight and from whatever course proceeding, if it be in any degree profitable to the individual of any species... will tend to the preservation of that individual, and will generally be inherited by its offspring. The offspring, also, will thus have a better chance of surviving, for, of the many individuals of any species which are periodically born, but a small number can survive. I have called this principle, by which each slight variation, if useful, is preserved, by the term of Natural Selection, in order to mark its relation to man’s power of selection.’ In this instance, once dairy farming had developed in Europe, the increased exposure to milk (and the benefits associated with drinking milk – see later) meant that the few people who had the mutated, lactase-persistence allele were more likely to survive, therefore more likely to mate and thus more likely to pass on their alleles to their offspring. Gradually over many, many generations this has increased the allele frequency and totally reversed the ratio of lactose intolerant:tolerant in the areas of the world with a significant pastoral history.

This suggests that having a lactose tolerance is an evolutionary advantage, where milk is readily available. In areas such as China, where milk and dairy products are not widely consumed, the mutated allele remains in a very small minority. There is much speculation as to why this lactase-persistence allele is so advantageous. Milk is uncontaminated by parasites, unlike stream water, making it a safer drink. Also, if those that were intolerant of lactose tried to drink the milk, they would develop diarrhoea and vomiting – this could be lethal in difficult living conditions and they could therefore die of dehydration in the most extreme cases. Another suggestion is the benefit of having a continuous supply of milk as opposed to seasonal crops – cows will give milk all year round whereas crops can only thrive at certain times in the year. Also, milk has many nourishing properties – it is high in fat and calcium, amongst other nutrients. All in all, the ability to drink milk gave some early Europeans and East Africans a big survival advantage. As a result, 30 per cent of European adults are still lactose intolerant (i.e. do not have the lactase-persistence allele). Of these people, 24 per cent actually have secondary lactose intolerance as a result of coeliac disease. In coeliac disease, the body produces antibodies to the gluten in wheat products. This causes inflammation and damage to the villi in the small intestine, especially to the apical region (where the concentration of lactase is highest). Thus a sufferer of coeliac disease could be temporarily lactose intolerant for a few years (eventually, with a gluten free diet, the patient’s gut is able to fully heal). This could mean that the percentage of the population without a mutation for lactose persistence could be even lower than 30 per cent.

In conclusion, the evolution of lactose tolerance is a very good example of natural selection that has occurred in certain populations in different parts of the world in relatively recent times. Lactose tolerance is caused by an inherited mutation that causes lactase production to continue throughout adulthood.

Why do humans reproduce sexually?

2009-02-19T05:00:00.000-08:00

The evolution of sexual reproduction is not widely discussed or questioned in non-academic circles, it is taken as a given that humans, and the majority of species throughout time, reproduce through the fusion of gametes. Yet it is uncertain whether this is the most efficient and secure way of continuation of our species. Asexual reproduction is accepted as the most rapid way to expand a population from one generation to the next, as described by John Maynard Smith,[1] so why do humans not reproduce in such a way? Many theories have been put forth for all sexually reproducing species, some only apply to certain species and many explanations intertwine with one another. One justification is the increased capacity for genetic variation to occur, which links closely to the hypothesis that sexual reproduction is primarily in order to resist parasites. Both are countered by the suggestion that the occurrence is necessary to remove deleterious genes or is an adaptation to substantial chromosomal damage and mutation. These theories have been combined along with my own thoughts in order to ascertain in my own mind why Homo sapiens have evolved to reproduce sexually.

Charles Darwin, the father of modern evolutionary thinking, stated that the advantage of sex is “the offspring of two individuals, especially if their progenitors have been subjected to very different conditions, have a great advantage in weight, constitutional vigour and fertility over the self fertilized offspring from either one of the same parents.”[2] Thus he suggests that a genetically superior individual is created by two sexes, rather than asexually. This supports the hypothesis of repair and complementation, or hybrid vigour, where genetic recombination and outcrossing are adaptations to chromosome damage and mutation. It is suggested that recombination during meiosis (and thus sexual reproduction) is primarily required in order to repair damaged DNA. However, this contradicts the widely accepted suggestion that recombination evolved primarily to increase genetic variation between parent and offspring. Therefore if Darwin were still to maintain the significance of recombination in the evolution of sexual reproduction then his theory would have to move more to support the view that sex chiefly occurs in humans in order to maintain variation. Nevertheless, as will be pointed out later, it is questionable how vital variation is to specifically the human race. In addition, it has been put forth by the likes of Elshel that recombination disrupts positive combinations of genes more often that it creates them.[3] Consequently there are evident flaws in Darwin’s suggestion and the repair and complementation hypothesis, particularly relating to the original purpose and importance of recombination during meiosis.

Darwin’s thought that the birth of a genetically stronger human is the main reason for the evolution of sex points to the ability to survive, and thus can be linked with the Red Queen Hypothesis,[4] where the fundamental advantage of sexual reproduction over asexual reproduction is the resistance to parasites. This hypothesises that the underlying purpose of sexual reproduction is to allow enough genetic variation for evolution to occur quickly enough to maintain a population despite the evolution of its parasites. This seems to suggest that sexual reproduction is not only an outcome of evolution, but also the cause of continued evolution once it manifested itself in our ancestors. Ridley’s theory is currently the most dominant in terms of support from leading academics, and can be applied directly to human evolution, convincingly arguing why asexual reproduction does not occur in Homo sapiens.

The basic purpose of natural selection seems to be survival. This depends on the ability to adapt to a change in the environment, usually through an increase in variation and the size of a species’ gene pool. Thus this statement seems to relate to the genetic variation that is supposedly necessary in the Red Queen Hypothesis. This opinion is also directly supported by Weismann’s original theory that the advantage of sexual reproduction is variation between siblings.[5] Ghiselin supported this with the Tangled Bank Hypothesis[6] that suggests an assorted population of siblings may be able to extract more food from their environment. However, this poorly applies to humans due to the relatively few siblings that are produced throughout our evolution, along with the fact that Homo sapiens are a highly homogenous species – DNA between individuals is very similar. Sex may also be necessary due to the greater ability it has over asexual reproduction to produce new genotypes. This again puts emphasis on the influence of recombination, that allows for two advantageous alleles on the same chromosome of different individuals of a population to eventually combine. In an asexual population it would take a mutation for a chromosome to gain the two alleles. However, this theory depends on group selection, a weaker selective force than natural selection, as individual fitness is not the motivating factor, but benefit to the group is. This is due to the Two Fold Cost of Sex, put forth by John Maynard Smith,[7] whose theory states that asexual reproduction would bare more young than sexual reproduction. In addition the two sexes have to find one another and are only attracted to certain features. Therefore it is unlikely advantageous alleles would come together within a population. However, the Two Fold Cost of Sex has been countered by the fact that species that can produce by both means choose to reproduce sexually over asexually whenever they can. This points to an overall advantage of sexual reproduction in terms of the central theme of survival. Yet, if the main purpose of sexual reproduction in humans is simply survival, then why has the evolution of feeling such as love occurred? It may be suggested that love has the purpose of leading to reproduction, yet without love there would be more indiscriminate mating within the species, increasing variation within the human population. Therefore survival through variation of a species may not be the main purpose of sexual reproduction, drawing more support towards the Red Queen Hypothesis.

Whereas the Tangled Bank Hypothesis refers to recombination of advantageous genes, there is also a theory that the purpose of sexual reproduction is to remove harmful genes caused by mutation through natural selection. Kondrashov’s theory, the Deterministic Mutation Hypothesis,[8] suggests that because each mutations is only slightly damaging, they will accumulate from one generation to the next until the individuals that have gained many mutations die. However, he writes that there must be at least one adverse mutation per generation, per genome, for the theory to apply. This is feasible for humans because of the “genomic deleterious mutation rate … [of] at least 3”[9] in Homo sapiens.

All the above-mentioned approaches hold some weight in determining the reasons for the evolution of sex in humans. The repair and complementation hypothesis is said to result in a human being that has a greater chance of survival, along with the theory that genetic variation is the core reason for sexual reproduction. The Red Queen Hypothesis primarily centres on the ability of sex to allow for greater variation, so other than the Deterministic Mutation Hypothesis, variation is a common theme throughout. This is also the backbone of Darwin’s theory of Natural Selection, where variation leads to individuals with advantageous genes passing these characteristics onto their offspring. Despite the more rapid reproductive potential of agamogenesis, variation, and thus a greater chance of survival, is evidently the advantage that sexual reproduction brings to Homo sapiens.

[1] J. M. Smith, The Evolution of Sex, 1978
[2] C. Darwin, The Effects of Cross and Self
[3] Eshel and Feldman 1970
[4] M. Ridley, The Red Queen: Sex and the Evolution of Human Nature, 1995
[5] A. Weismann, Essays on Hereditary and Kindred Biological Subjects
[6] M. Ghiselin, The Economy of Nature and the Evolution of Sex, 1974
[7] J. M. Smith, The Evolution of Sex, 1978
[8] http://www.nature.com/nature/journal/v336/n6198/abs/336435a0.html
[9] http://eebweb.arizona.edu/nachman/pdfs/nachman_crowell_2000b.pdf

Should being a creationist automatically disqualify applicants for admission to medical school?

2009-02-19T01:04:00.000-08:00

Before answering this question I will explain what being a creationist means, and the different types of beliefs a creationist can hold. Then I shall go on to explore the reasons why you might want to disqualify a medical school applicant on the grounds of being a creationist, the reasons why being a creationist and medical student should not matter, and then reach a conclusion.

Creationism is the belief that each species was created separately, in its current form, by God. It has experienced a rise in popularity in the last century, especially in America. In a 2005 survey, it was found that 42% of Americans believe that ‘humans and other living things have existed in their present form since the beginning of time’.1 Creationism encompasses many different beliefs – the main ones being Young-Earth and Old-earth creationism, which I will explain further.

Young earth creationism is the belief that the bible is literally true; that God created the world in 6 days, and that the world is between 6,000 and 10,000 years old as according to the bible, rather than 4.5 billion years according to most scientists. 2 Young-earth creationists generally view the bible as equal to textbooks in scientific accuracy. A 2009 survey by the Theos Think Tank showed that 11% of people in the UK believed that ‘God created the world sometime in the last 10,000 years’, and 21% thought it was probably true. 1

Old earth creationism itself encompasses several categories such as gap creationism, day-age creationism and progressive creationism, although what defines it from young-earth creationism is the belief that the earth is 4.5 billion years old, rather than 10,000 years old as a literal belief in the bible would make it. Gap creationism is the belief that there was a long period of time between God creating the earth, and the rest of the creation story. Day-age creationists believe that each ‘day’ in the creation story refers to a non-specific period of time (perhaps millions of years) rather than 24 hours. Progressive creationists believe that creation was a progressive, gradual process involving evolution within species (microevolution), but new species were created by God’s intervention and not evolution.

Intelligent Design is a recently-developed belief which stemmed out of creationism. Believers in this theory do not agree with natural selection as the driving factor for evolution, as this is an ‘unguided, purposeless change.’ 3 They believe the best explanation for the complexity of life and the universe is the existence of an intelligent creator.

On one hand, there is an argument that being a creationist should disqualify you from medical school. If the medical student decides to go into research, they may be biased by their creationist views, which may then hinder scientific progress. ‘Creation Science’ is where creationists try to use scientific research to prove the Genesis account of creation, and has been consistently rejected by scientists as valid research. As Darwin himself said, ‘we can only say that…it has pleased the Creator to construct all the animals and plants…but this is not a scientific explanation’.4 It includes creation biology, which attempts to prove that different species did not originate from the same ancestor, and flood geology, which tries to show how a world flood as documented in the bible is compatible with geological evidence. Many of these theories for flood geology were published in the book ‘The Genesis Flood’ by Morris and Whitcomb in 1961. 5 The popular geology journals of the time completely ignored the book, and one review by the ‘ASA Journal’ called them ‘pseudo-scientific pretenders’. Yet despite all this, creation science was taught in many American schools. In 1921, the Butler Act in Tennessee disallowed publicly funded teachers ‘to teach any theory that denies the Story of the Divine Creation of man as taught in the Bible, and to teach instead that man has descended from a lower order of animals’, and this was the law until 1967. This could not have progressed scientific education.

Furthermore, if a medical school applicant was a young-earth creationist, this may suggest that their personality is unsuited to that of a doctor. There is overwhelming scientific evidence for the earth being 4.5 billion years old. Examples of this are radiometric dating, which uses the half-lives of radioactive elements in rocks to determine their ages, observing ice cores, and dendro-chronology – analysis of annual tree rings. 2 An inability to accept this evidence might demonstrate an inflexible, irrational personality. This would be disadvantageous as a doctor, where the ability to work in a team and to consider many different viewpoints is crucial. They might hold their views on contentious issues such as abortion very strongly, perhaps influencing a patient on important decisions and not giving them a balanced view.

However, there are also many arguments why being a creationist should not disqualify an applicant from medical school. To begin with, being a creationist does not necessarily affect the quality of care that a doctor would give a patient, so it is an irrelevant criterion to judge a potential medical student by. Perhaps if they were a young-earth creationist this might indicate more radical views, but old-earth creationists agree with some scientific views such as the age of the earth. Thus they will be less likely to hold radical views on other topics, and other factors such as communication skills and academic ability should be considered more significant. Their belief might even be considered a positive attribute – it suggests they know where they stand on difficult issues, and as a result are wiser, more thought-out doctors.

Furthermore, as creationists believe each species was created separately by God, they may have a high regard for human life, of value as a doctor. The concept of evolution is that the fittest survive and breed, the weaker die out. At the time this led to the belief of eugenics – ‘good genes’. Darwin’s cousin, Dalton, recommended that the fitter, more intelligent, are encouraged to breed, and the less fit are discouraged. Later, this belief was taken up by Hitler, who wanted to rid the world of ‘inferior races’ and populate it with a pure, arian race – a line of thinking totally and utterly opposed to medicine. Perhaps the compassion and desire to help others needed as a doctor is found more in creationist views than in evolutionary principles.

In Conclusion, I believe that it depends on the type of creationist that you are. There is an argument to disqualify Young-Earth Creationists from medical school, as they are disagreeing with a large amount of scientific research on the topic. They might make more irrational doctors and, if they were to go into research, may hinder scientific progress. In terms of other creationist views, as long as these beliefs do not adversely affect your treatment of a patient, it should not disqualify you. It may even suggest the student is more thought-out, and holds human life in high regard – a valuable characteristic for a doctor. Finally, in a letter, Darwin once wrote: ‘There is no reason why the disciples of [religion and science] should attack each other with bitterness, though each upholding strictly their beliefs.’6

References:
1.‘Rescuing Darwin: God and evolution in Britain today’ Nick
Spencer and Denis Alexander, 2009:
Chapter 2: God after Darwin: The twentieth century and the
rise of creationism. Page 26.
Chapter 3: Darwin today. Pages 29-33.
2.‘The Rough Guide to Evolution’ Mark Pallen, 2009.
Creationism: A House Divided, page 284.
How we know the earth is old, pages 12-13.
Can a Christian believe in evolution, pages 280-281.
3. ‘Testing Darwinism’ Philip E Johnson, 1997.
 Chapter 1: Emilio’s Letter. Page 16.
4.‘The Origin of Species’ Charles Darwin, 1859.
Chapter XIV: Morphology. Page 383.
5. ‘The Genesis Flood’ Morris and Whitcomb, 1961.
6.A Letter from Darwin to his friend and local vicar, John Brodie
Innes, on November 27th, 1878.

HeLa Cells

2009-02-18T09:24:00.000-08:00

“HeLa Cells: ethical nightmare, medical blessing, or evolution of a post-human species?”

HeLa cells are known globally as one of the greatest medical discoveries of our time, and allowed for many - if not all - important medical advances that have occurred during this century. However, despite their unarguable medical importance, their existence is shrouded in controversy, whether it be in their origin, their continual usage, or in the revelation of their unique chromosome number.
The story of HeLa cells begins with Henrietta Lacks, a young mother of five who lived in Baltimore during the 1940-50’s. On February 1st 1951, at Hopkins Hospital, Henrietta was found to have malignant cervical cancer. At the same time in the hospital, the Head of tissue culture research, George Gey, and his wife Margaret, where working to find a cure for cancer. They were sure that if they could culture a line of human cells that could live indefinitely outside of the body, then the cure would soon follow. A sample of Henrietta Lack’s cancer cells were taken, and a young resident who knew that the Geys’ where searching for a new sample to investigate, sent it to the George Gey. Henrietta’s cells turned out to be the break-through that Gey had been waiting for - her cells multiplied like no-one had ever seen before, reproducing an entire generation every 24hours; they were an immortal cell-line, with the acquired ability to proliferate continuously, without any mechanisms of prevention. Gey named the cells “HeLa cells”, in honour of their source’s name, but claimed them as his own discovery, and spent the rest of his life profiteering from them.
This is when the first ethical dilemma arises; Henrietta Lacks had no idea that a sample of her tumour had been taken and sent to George Gey, and that her own cells would be used as a basis for medical research for decades to come. Her husband David knew that a sample had been taken, but was told that it was to see if the cancer was hereditary, and that it might help his children if the cancer struck again. Despite being told this, David Lacks never heard from the research team again. There is a question then, of whether appropriate consent was given. Having looked into this topic, however, I have found that there is no legal requirement to inform the patient or patient’s family in such a case, as any tissue obtained/removed by the physician during surgery, or indeed any medical procedure, in fact then becomes the property of the surgeon, to do with what he/she pleases. Personally, I find this to be an unorthodox rule, particularly in the case of Henrietta Lacks, when the physician in question profited so greatly from the sample he obtained. However, lack of informed consent was common in medical research at the time.
On the 4th October 1951, Henrietta Lacks passed away, and on the same day George Gey appeared on national television with a vial of his “HeLa” cells, stating “It is possible that, from a fundamental study such as this, we will be able to learn a way by which cancer can be completely wiped out.”
Soon after this statement was made in front of the American nation, the HeLa cell-line was used to propagate poliovirus, which then lead to the development of vaccines against polio, a medical triumph that saved thousands of lives, and one that could not have occurred where it not for the unique nature of HeLa cells. In this scenario, we can indeed classify HeLa cells as a “medical blessing” - the fact that Gey and his team managed to propagate the poliovirus so quickly lead to a surge of global interest in the HeLa cell line, and facilities to enable mass-production of HeLa cells was established by the National Foundation for Infantile paralysis. Soon samples of Henrietta’s cells were being bought and sold by millions world-wide, and even went up in the first space missions to see what would happen to human cells in zero gravity.
Here the second ethical dilemma appears. Henrietta’s family had no idea that her cells were being used in such a way - they weren’t ever aware they were still alive. It wasn’t until 24 years after death, when her daughter in law heard about them from a scientist at a dinner party, that the issue came to their attention. The family were unable to afford a lawyer to take the case to court, and so nothing could be done about what the Lacks family believed to be a great injustice. One of Henrietta’s daughters is quoted to have said "We never knew they took her cells, and people done got filthy rich, but we don't get a dime"
As I stated earlier, the HeLa cell-line can be classed as a “medical blessing” as they allowed for previously impossible medical research to be carried out. It can be argued, however, that HeLa cells turned out to be more of a medical curse. After the discovery of HeLa cells, as more and more laboratories began using human cells in culture, scientists were finding that since the introduction of HeLa cells, these other cell cultures also began to multiple indefinitely. For two decades research was done on what were thought to be normal human cells, for example placental cells, but in 1974 it was revealed that HeLa cells - due to their robust nature and ability to spread and multiply so considerably - had contaminated the world’s stock of cell cultures. This meant that billions had been spent on isolated tissue cultures, that turned out to be invalid as they were revealed to be HeLa cells. Although this caused obvious setbacks in the scientific world, I think that some good may have come out of it, as the methods of preparation and study of cell cultures has been vastly improved since then, meaning the potential for human error has been significantly reduced.
Hopefully I have explained sufficiently the ethical and medical dilemmas surrounding the immortal HeLa cells, but what of the other question of the evolution of a post-human species? This question arises when we look at some of the unique features of HeLa cells; mainly that they are unarguably human - haven been extracted directly from a human source - but equally they have 82, instead of 46, Chromosomes in their nuclei (four copies of chromosome 12 and three copies of chromosomes 6, 8 and 17). In theory, if a HeLa cell could produce a gamete, it would not be able to fertilize with a human gamete (due to the different number of chromosomes) - which, by laws of classification, means that HeLa cells are an entirely new species - Helacyton gartleri - to use it’s proper given name.
It would appear that through the mechanism of random mutations, the cervical cancer cells in Henrietta Lacks body found a selective advantage, that allowed them to proliferate indefinitely and to live for an extended length of time. But what is this selective advantage that has allowed HeLa cells to flourish? Research has shown that HeLa cells have an active form of the enzyme Telomerase (not present in normal cells, but can be found in most cancerous cells). Telomerase is active during cell division, and prevents the shortening of telomeres - a mechanism that is associated with ageing and eventual cell death.
It may be argued then, that cancer cells are a mode of “microevolution“; the cells within us are subject to the same laws of natural selection as we are, with HeLa cells emerging as the next branch of the evolutionary tree.
To conclude, I think that HeLa cells are all of an ethical nightmare, medical blessing, and evolution of a post-human species. The Lacks family never gave their consent for Henrietta’s cells to be used in research, neither did they receive any acknowledgment for the great medical advances Henrietta gave to the world. However, since the cells are technically not human, does the family have any right to them? Certainly this can be classified as an ethical nightmare.
From looking at the medical advances HeLa cells have provided, I would agree that they are a medical blessing, especially in light of their ability to keep their telomeres intact, which is now being used in medical research to see if the same mechansim can elongate human life.

http://www.citypaper.com/news/story.asp?id=3426
http://www.jhu.edu/~jhumag/0400web/01.html
http://home.ncifcrf.gov/ccr/lgd/human%20genetics%20pdfs/MS447_O'Brien_PNAS.pdf
https://knol.google.com/k/eli-vieira-araujo-jnior/aging-and-immortality-in-biology

Purpose of this blog

2009-02-16T02:44:00.000-08:00

This blog has been created by Professor Mark Pallen for the purpose of allowing medical students to blog on selected topics during a one-week student-selected activity. Students who choose to blog, should post their work (1000-2000 words) by 5pm on Thursday 19th February 2009.