| Menopause, Maternal Investment and Physical Anthropology: Physical anthropologists attempt to explain why and how certain adaptations have taken place in human developmental history. For many years the phenomenon of human menopause baffled anthropological experts. If reproduction is in fact the prime directive of natural selection then menopause, or genetically heritable infertility, would seem completely anomalous from an evolutionary standpoint. Furthermore, with the exception of humans, periods of post reproductive infertility are extremely rare among mammals. So what makes us different? In the last decade a theory has been developed that explains why prehistoric, human females developed menopause and how an inability to create offspring could have conferred an evolutionary advantage upon the human species. The answer seems to be two fold and our discussion will concentrate on the risks associated with childbirth and the relative importance of parental investment to the human species. It is conceivable that older mothers that lost their sexual viability were able to spend more of their time helping, protecting and teaching their children and grandchildren. Such an investment of time is referred to by behaviorists as parental investment, or altruism. Experiments and natural observation have shown that those animals that have had time invested in them by family members, in the form of protection and teaching, are much more likely to live to the age at which they are able to reproduce. This means that menopausal mothers in prehistoric times were better equipped to ensure the survival of their offspring. Both pregnancy and childbirth are extremely detrimental to the health and longevity of women. Pregnancy increases a woman’s caloric intake requirements and childbirth exposes women, especially older women, to deadly infections. For these reasons physical anthropologists have reached the consensus that primitive, older women were less productive child bearers than younger women. On average those women who experienced menopause lived longer lives and were better able to spend time supporting their children and their grandchildren. The progeny of these menopausal women benefited from additional parental investment and were thereby more likely to live to procreate. These progeny also benefited from inheriting their mother’s genes because these genes caused them to experience menopause and have more prosperous progeny of their own. Thus menopause in older woman today is a remnant of a protective evolutionary adaptation that allowed females to better focus their maternal resources. Authors that furthered the development of this theory of menopause include Kristen Hawkes (the creator of the "Grandmother Hypothesis") and C.G. Williams who first posited that menopause may be protective. |
| Organization for the Advancement of Interdisciplinary Learning |