• Posted October 27, 2023

Female Chimps May Experience Menopause, Too

New research finds the first proof that wild female chimpanzees experience menopause, similar to humans.

The study was part of two decades of research in the Ngogo community of wild chimpanzees in western Uganda's Kibale National Park.

"In societies around the world, women past their childbearing years play important roles, both economically and as wise advisers and caregivers,"said first study author Brian Wood, an associate professor of anthropology at the University of California, Los Angeles. "How this life history evolved in humans is a fascinating yet challenging puzzle.

"The [study] results show that under certain ecological conditions, menopause and post-fertile survival can emerge within a social system that's quite unlike our own..."Wood said in a UCLA news release.

What researchers found is that fertility among the chimpanzees declined after age 30. No births were observed after age 50.

The findings were published Oct. 26 in the journal Science.

Before this study, menopause and post-reproductive survival had been found among mammals in a few species of toothed whales. Among primates, it had only been seen in humans.

This new data can help researchers better understand why menopause and post-fertile survival occur in nature, and how it evolved in the human species.

To study this, 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 of the females. They also measured hormone levels in urine samples from 66 females of varying reproductive statuses and ages. The females ranged in age from 14 to 67 years.

"This study is the result of an extraordinary amount of effort,"said study co-author Jacob Negrey, an assistant professor in the School of Anthropology at the University of Arizona.

"It's only because our team has spent decades monitoring these chimpanzees that we can be confident some females live long after they've stopped reproducing," Negrey said in the release. "We also spent thousands of hours in the forest to collect urine samples from these chimpanzees with which to study hormonal signals of menopause."

The researchers measured hormone levels associated with human menopause. This includes increasing levels of follicle-stimulating hormone and luteinizing hormone and decreasing levels of ovarian steroid hormones including estrogens and progestins.

Hormone data showed that the Ngogo chimp females experienced a menopausal transition similar to that of humans, beginning around age 50.

It was not unusual for these female chimpanzees to live past 50, like their human counterparts. A female who reached adulthood at age 14 was post-reproductive for about one-fifth of her adult life, according to the study. That's 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 socioecological 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,"Wood said.

It will be critical to track the behavior of older chimpanzees and observe how they interact with and influence other group members, the researchers noted.

More information

The World Wildlife Foundation has more on chimpanzee research.

SOURCE: University of California, Los Angeles, news release, Oct. 26, 2023