This is the first proof of menopause in wild chimpanzees

UCLA’s latest study on the Ngogo chimpanzee community in Uganda challenges previous understanding, providing undeniable proof of menopause and post-fertile survival in wild chimpanzees.

Research conducted on the Ngogo chimpanzee community in Uganda has unveiled groundbreaking findings, revealing that human beings are not the only primates to experience an extended post-fertile phase of life.

Over the course of two decades, a dedicated team of researchers at Kibale National Park in western Uganda has been studying the Ngogo community of wild chimpanzees. Their findings, which were recently published in Science, indicate that female chimpanzees within this community undergo menopause and exhibit signs of post-reproductive survival.

Before this pivotal study, titled “Demographic and Hormonal Evidence for Menopause in Wild Chimpanzees,” such characteristics were only documented in a select few mammalian species, specifically certain toothed whales, and among primates, exclusively in humans.

This new compilation of demographic and physiological data will provide a vital resource for researchers aiming to delve deeper into the origins of menopause and post-fertile survival in the natural world, as well as its evolutionary trajectory within human beings.

First Evidence of Menopause in Wild Chimpanzees

Brian Wood, an Associate Professor of Anthropology at UCLA and the leading author of the study, adds, “In societies around the world, women past their childbearing years play important roles, both economically and as wise advisors and caregivers. How this life history evolved in humans is a fascinating yet challenging puzzle.”

Wood collaborated extensively with Kevin Langergraber from Arizona State University, Jacob Negrey from the University of Arizona, as well as John Mitani and David Watts, who are founders and co-directors of the Ngogo Chimpanzee Project.

Wood explains that the study’s outcomes demonstrate that menopause and post-fertile survival can manifest in social structures vastly different from human ones, even in the absence of grandparental support.

This challenges the commonly accepted grandmother hypothesis, which has been used to explain postmenopausal survival in humans, suggesting that older females can enhance their genetic legacy by assisting in the upbringing of their grandchildren.

In contrast to humans, older female chimpanzees typically do not reside near their daughters or participate in grandchild care. However, the Ngogo females frequently live beyond their reproductive years. This discovery poses the question of whether such post-reproductive longevity is a temporary adaptation to the chimpanzees’ current ecological conditions, or if it is an intrinsic species-specific trait that has been overlooked due to recent human-induced negative impacts.

To arrive at these conclusions, the research team meticulously analyzed mortality and fertility data of 185 female chimpanzees, collected from 1995 to 2016. They also measured hormone levels in urine samples from 66 females of varying ages and reproductive statuses, spanning from 14 to 67 years old. These measurements were crucial for identifying hormonal indicators of menopause.

The hormone data revealed a menopausal transition in the Ngogo females, commencing around the age of 50, similar to that observed in humans. Remarkably, it was not uncommon for these female chimpanzees to surpass the age of 50, spending approximately one-fifth of their adult life in a post-reproductive state.

Brian Wood emphasizes, “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.”

They emphasize the importance of monitoring the actions of the older chimpanzees, as well as examining their interactions with and impact on the rest of the group members.

“To allow such work, it is essential to support the long-term study of primates in the wild,” Wood adds.

Source: Science

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