In most animals, relatively few females live past reproductive age. Humans are the notable exception to this. n his book The Accidental Species: Misunderstandings of Human Evolution, Henry Gee writes:
“In human females the process of menopause marks a definite shutdown of reproductive capacity—after which the individual can expect to live for several more decades.”
Speaking from a biologically evolutionary viewpoint, and, particularly with an awareness of natural selection, we must ask: What is the reproductive advantage to menopause, to having females live beyond their reproductive years?
One of the many ramifications of bipedalism and the big brain is that humans must be born prematurely in order to fit through the birth canal. This means that most of the physical growth of the brain has to take place after birth. In their book From Lucy to Language, Donald Johanson and Blake Edgar write:
“Even though the human gestation is relatively long and the infant emerges large for its mother’s body size, the human brain is born premature.”
While human gestation is only nine months, the actual gestation period for the human brain is 21 months. This means that human infants have a long period in which they require care. This means that helpless human babies require care. Henry Gee writes:
“Because human babies take so long to mature, one can imagine selective value in both prolonging human female life span and introducing a definite cessation of reproductive effort in order to care for one’s grandchildren, as well as one’s own children—rather than producing more children who will compete for resources with one’s grandchildren.”
Thus, one of the implications of menopause for early social organization is that among humans, grandmothers may be available for child care and enculturation. Henry Gee explains:
“It is known—or at least strongly suspected—that women who can call on relatives to help raise children do so more successfully than those for whom help is unavailable. In traditional societies, at least, a great deal of help comes from a mother’s older female relatives, especially her own mother. This so-called grandmother hypothesis might explain another otherwise puzzling feature of human biology—the menopause.”
Let us take a quick ethnographic explanation of kinship terminology. In modern societies, the term grandmother is generally used in reference to two people: a person’s father’s mother and a person’s mother’s mother. While this seems to imply that each person has only two grandmothers, in many other societies, each person has many different grandmothers (and, often, many mothers). The concept of grandmother, in many societies, particularly in hunting and gathering societies, is not restricted to close biological relatives but is expanded to include fictive and adopted relatives as well. In some societies, grandmother is an honorific term used in referring to a woman elder.
Grandmothers may have been an important element in the evolution of culture, and in the processing of passing culture from one generation to the next (technically called enculturation). Henry Gee writes:
“By offering stores of knowledge that can be passed on to younger members of a group, elders make societies more cohesive and offer the potential for such groups to become more complex.”
Is the phenomenon of grandmothering an ancient cultural tradition? In his book Human Evolution,Robin Dunbar suggests that it is not:
“That grandmothering may be a very late evolutionary development is suggested by that fact that the fossil evidence clearly shows that it is only with the appearance of anatomically modern humans that a significant number of individuals survived to an age where they could be grandparents.”
In a report in Becoming Human: Our Past, Present and Future, Kate Wong writes:
“…around 30,000 years ago, the number of modern humans who lived to be old enough to be grandparents began to skyrocket. Exactly what spurred this increase in longevity is uncertain, but it meant that people had more reproductive years and more time over which to acquire specialized knowledge and pass it on to the next generation.”
In modern human females, menopause usually occurs between the ages of 45 and 55. Assuming that menopause occurred at this same age for human ancestors, particularly for pre-sapiens ancestors, may not be valid. While the fossil record may provide information about age at death, it doesn’t really provide information about menopause.
More Human Origins
Human Origins: The Great Chain of Being
Human Origins: Cultural Evolution
Human Origins: The Mind
Human Origins: The Large Brain
Human Origins: The Human Hand
Human Origins: Bipedalism
Human Origins: Sexual Selection