A female chimpanzee from the Ngogo community in western Uganda. Credit: The Ngogo Chimpanzee Project
Key points:
- Female chimpanzees in Uganda’s Ngogo community experienced a menopausal transition similar to women.
- Fertility among chimpanzees studied declined after age 30, and no births were observed after age 50.
- The data can help researchers better understand why menopause and post-fertile survival occur in nature and how it evolved in the human species.
A team of researchers studying the Ngogo community of wild chimpanzees in western Uganda’s Kibale National Park for two decades has published a report in Science showing that females in this population can experience menopause and post-reproductive survival.
Prior to this study, these traits had only been found among mammals in a few species of toothed whales, and only in humans among primates. These new demographic and physiological data can help researchers better understand why menopause and post-fertile survival occur in nature, and how it evolved in the human species.
For the research, UCLA researchers examined mortality and fertility rates of 185 female chimpanzees from demographic data collected from 1995 to 2016. They calculated the fraction of adult life spent in a post-reproductive state for all the observed females and measured hormone levels in urine samples from 66 females of varying reproductive statuses and ages, ranging from 14 to 67 years.
As with other chimpanzee populations and humans, fertility in the chimpanzees studied declined after age 30, with no births observed after age 50. The hormone data showed that the Ngogo females experienced a menopausal transition similar to that of humans, beginning around age 50.
Also like humans, it was not unusual for these female chimpanzees to live past 50. A female who reached adulthood at age 14 was post-reproductive for about one-fifth of her adult life, about half as long as a human hunter-gatherer.
“We now know that menopause and post-fertile survival arise across a broader range of species and socio-ecological conditions than formerly appreciated, providing a solid basis for considering the roles that improved diets and lowered risks of predation would have played in human life history evolution,” said Brian Wood, UCLA associate professor of anthropology and first author of the study.
The researchers say it will be critical to track the behavior of older chimpanzees and observe how they interact with and influence other group members in the future.