Female Gorillas Go Through Menopause, Zoo Study Shows

Stefan Lovgren
for National Geographic News

December 27, 2005

They may not experience hot flashes, mood swings, or migraines, but female gorillas reach menopause just like human women do, according to a new study of gorillas at 17 U.S. zoos.

"Menopause has typically been viewed as a strictly human phenomenon," said Sylvia Atsalis, a primatologist at Brookfield Zoo in Chicago, Illinois, who co-directed the study. "Now we know that may not be the case."

The findings may not only improve the care of aging female gorillas but could also shed light on the human female reproductive cycle.

"Our findings underscore the similarities between humans and gorillas, our evolutionary cousins, who may be good models for an improved understanding of menopause [in humans]," Atsalis said.

Sexual Interest

The study began in 2002 as a pilot project at Brookfield Zoo.

Atsalis and a colleague, Sue Margulis, now a curator of primates at Chicago's Lincoln Park Zoo, wondered whether a gorilla named Alpha, born in 1961, should be given contraceptives to prevent her from becoming pregnant.

She showed considerable sexual interest in Ramar, the group's silverback. Once a month she would sit and stare at him intently, toss hay, and even attempt to sit in his lap.

But zoo staff feared that Alpha wouldn't be able to properly care for a baby because of her age.

Gorillas in zoos can live to be 50 or older, but females very rarely have babies after age 37.

The study that began with Alpha soon expanded to include 30 aging female gorillas at 17 zoos around the country.

The researchers tracked the hormonal cycles of the females by collecting fecal samples to check the levels of progesterone, a reproductive hormone.

"Our goal was to determine if geriatric female gorillas were still [menstrual] cycling or whether they showed patterns suggestive of menopause," Margulis said.

The results showed that about 25 percent of the female gorillas were menopausal, meaning their monthly hormonal cycles had ceased.

Another 32 percent appeared to be perimenopausal. In humans, this refers to the 5 to 10 years before menopause, when related physiological changes begin.

"We were quite excited by the significant parallels that we found between gorillas and human females in their life stages," Margulis said.

"Like humans, [gorillas] seem to go through perimenopause—where there are hormonal changes and reduced likelihood of conception—and then menopause."

Alpha was still having her menstrual cycle but showed possible perimenopausal symptoms. She was not placed on contraception, given the very low probability of conceiving at her age.

Biological Mystery

The findings could aid researchers' understanding of the physiological changes that occur at menopause, including diseases linked to the onset of menopause.

"Perimenopause may be the next big thing [in research]," Atsalis said. "Recent research shows this is a time when women should pay a lot of attention to their health to prevent bone loss and cardiovascular disease."

The research may also shed light on questions about the biological purpose of menopause.

In addition to humans, gorillas, and a handful of other primates, the only other animal known to live well past its reproductive years is the short-finned pilot whale.

It remains a mystery why some animals have evolved to live past their generative years while others haven't.

"As we continue to explore this issue in gorillas and in other apes, we should be able to understand better the significance of menopause: Is it a trait that has some evolutionary benefit, or is it an artifact of living longer?" Atsalis said.

Menopausal health will become even more important as humans continue to live longer, the researchers say. By 2025 an estimated 825 million women around the world will be over the age of 65.

"[People want] any kind of information to help in understanding menopause, especially when it comes from species that are so closely related to us," Margulis said.

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