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.
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