Chimpanzees, the species evolutionarily closest to humans, rarely experience menopause, according to an article published in the journal Current Biology last Thursday.

The study indicates that humans may be unique in their ability to survive decades past the onset of menopause, contradicting previous research that shows that chimpanzees and humans experience reproductive decline at the same rates.

The average lifespan of a chimpanzee is 15 years, and only seven percent live past the age of 40, according to the study. But of the 34 wild chimpanzees featured in the study that were older than 40, researchers found that almost half were able to give birth into old age, with one giving birth at the age of 55.

Unlike in humans, reproductive decline for chimpanzees was linked with a general decline in health.

“The individuals that experience reproductive decline are in relatively poor health,” said Melissa Emery Thompson, the lead author of the study and a post-doctoral fellow in anthropology.

In contrast, human females typically experience menopause between the ages of 45 and 55, but are able to live for many decades beyond that age.

One possible, and widely-accepted, explanation for this phenomenon in humans is “the grandmother hypothesis.”

According to Kristen Hawkes, a professor at the University of Utah and the originator of the hypothesis, grandmothers in “hunter-gatherer” societies were able to provide the key carbohydrates for their grandchildren, thereby giving those offspring an evolutionary advantage.

Emery Thompson’s study also helps confirm a hypothesis about why male chimpanzees prefer older females. Without menopause, older female chimpanzees are highly coveted since they have both the ability to reproduce and more experience as mothers.

Even though the study shows that menopause is an uncommon event for chimpanzees, Hawkes said that this may be because most die before they reach the average age at which they would normally experience menopause. The ones who survive to this age are genetically fitter.

But Hawkes—who has previously published work showing similarities in how humans and chimpanzees experience reproductive decline—said that determining whether chimpanzees experience menopause is a difficult task. Because chimpanzees are endangered, the sample sizes with which researchers like her and Emery Thompson work are almost always too small for definitive conclusions.

Emery Thompson’s study was co-written with a total of 10 other researchers, including Harvard anthropologist Richard W. Wrangham and renowned primatologist Jane Goodall.

—Staff writer Kevin C. Leu can be reached at kleu@fas.harvard.edu.

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