Researchers discover first proof of wild female chimpanzees experiencing menopause

A handful of mammals, including humans and toothed whales, are known to have extended lifespans in females beyond their reproductive years.

However, a recent study has uncovered the very first pieces of evidence of female wild chimpanzees experiencing menopause and having a post-fertile life, which has been very rare in the animal kingdom.

"Chimpanzees have been studied in the wild for a long time, and you might think there's nothing left to learn about them," senior author Kevin Langergraber of Arizona State University told news agency AFP. "I think this research shows us that's not true."

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Just like humans and other chimpanzee populations, a team of researchers from the University of California Los Angeles found out that fertility in western Uganda’s Ngogo community of wild chimpanzees declined after the age of 30, with no births observed after they aged 50.

After studying the mortality and fertility rates of 185 female chimpanzees at the Kibale National Park from the demographic data gathered from 1995 to 2016, the research team estimated the fraction of adult life spent in a post-reproductive state for all the females that were surveyed.

The hormone levels in the urine samples, collected from 66 female chimps were also measured by the researchers, linking it with the human menopause. It included an increase in the levels of follicle-stimulating and ovulating hormones, as well as decreasing levels of ovarian steroid hormones including estrogens and progestins. The chimps were of inconsistent reproductive levels and ages, varying from 14 to 67 years.

Ngogo females underwent a menopausal shift equivalent to that of humans, starting around the age of 50, said the researchers in their study published in the journal Science.

“The results show that under certain ecological conditions, menopause and post-fertile survival can emerge within a social system that’s quite unlike our own and includes no grandparental support,” said Brian Wood, UCLA associate professor of anthropology, referring to the grandmother hypothesis.

The researchers further found that just like humans, it was not distinctive for these female chimpanzees to live past the age of 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, they said.

“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 Wood.

(With inputs from agencies)

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