This is an archived story; this page is not actively maintained. Some or all of the links within or related to this story may no longer work.
For the latest University of Minnesota news, visit Discover.
Anne Pusey, director of the Jane Goodall Institute's Center for Primate Studies at the University, is an expert on chimpanzee behavior.
Chiimps and the change of life
A study on chimps renews debate on why menopause happens
By Deane Morrison
December 14, 2007
To some it brings blessed relief; to others, a heartbreaking loss of possibility. But whatever its personal significance, menopause has long been a subject of debate. The big question for researchers is why it evolved in the first place. Clues to human evolution are often found in our closest relatives, chimpanzees, whose ancestors split from ours sometime in the past seven million years. Now, a study of 172 wild chimps stirs the waters by reporting no evidence for a menopause-like event in the apes. If upheld, this finding would hand biologists the task of explaining how the timing of a major reproductive event evolved separately in two closely related primates. The study draws on data from chimpanzees at several sites in Africa, including Gombe National Park, where Jane Goodall began her pioneering work in 1960. The Gombe data is now stored at the University, in the Jane Goodall Institute's Center for Primate Studies. Its director, ecology professor Anne Pusey, is an author of the paper, which was published Dec. 13, 2007, online in Current Biology. The first author is Melissa Emery Thompson of Harvard University.
A big differenceThe researchers compared the chimps to hunter-gatherers in two tribes: the !Kung of Botswana and the Ache of Paraguay. In chimps and women, fertility, measured as births per female per year, declined similarly with advancing age, coming to a halt near the age of 50. Chimps tended to die off as they lost fertility, and so few survived beyond their reproductive period. But for women, survivorship didn't drop as steeply as fertility. Close to 40 percent of Ache and 60 percent of !Kung lived past reproductive age, with about 20 percent of !Kung living into their seventies. "This pins down that wild chimpanzees don't have a long post-reproductive life," says Pusey. "But even now, we don't have a good fix on wild chimp lifespan. The big question is, are people really different from apes, other primates, and other mammals in general with respect to the timing of reproductive [decline] versus [general bodily decline]?" According to Emery Thompson, the decline in fertility is something all animals are expected to experience if they live long enough. But menopause is unique in that it occurs because declines in reproductive function happen much faster than declines in other bodily systems. And indeed, the survivorship and fertility curves in the paper show a clear post-reproductive life for women but not chimps.
"The big question is, are people really different from apes, other primates, and other mammals in general with respect to the timing of reproductive [decline] versus [general bodily decline]?"Therefore, she says, scientists will have to "look to other unique features of human biology and socioecology to help explain why humans have menopause."