Gombe chimpanzees help shed light on questions about reproductive evolution
Data collected over several decades at JGI's Gombe Stream Research Center in Tanzania and other sites suggests that menopause – the period after which a woman's ovaries cease to produce eggs– may be a very human process not shared by our closest living relatives. In fact, nearly half of all wild female chimpanzees who live past the age of 40 continue to bear offspring.
The study, conducted by Harvard University's Melissa Emery Thompson and colleagues including Dr. Jane Goodall and Dr. Anne Pusey, head of JGI's Center for Primate Studies – were released in the December 18th issue of Current Biology. The study compared the reproductive life cycles of females from six chimpanzee populations to those of women from two hunter-gatherer populations – in Botswana and Paraguay.
The study shows that chimpanzees do not experience the extended "postreproductive" period that women do. That is to say, women will cease to produce eggs long before their overall health deteriorates, whereas the evidence indicates that the lack of reproduction in older chimps is most likely indicative of overall health. Only about 10 % of chimpanzees live past the age of 40.
"At this point there is no evidence of a menopausal period in chimpanzees," says Pusey. "Fertility declines in tandem with senescence in other body systems in chimpanzees, which is what we see in most other mammals."
The evolutionary benefit of an extended postreproductive period in women may relate to the benefits of having older women in communities – grandmothers -- who are able to assist younger mothers in provisioning their grandchildren. "Or it may occur more simply because human children need to be provisioned for much longer after they are weaned than other mammals, and mothers may benefit from ceasing reproduction and raising their youngest offspring to maturity," says Pusey.
The study, "Aging and Fertility Patterns in Wild Chimpanzees Provide Insights
into the Evolution of Menopause," can be found in the Dec. 18, 2007 edition of Current Biology. A summary can be found here.