No hot flashes, no mood swings, no migraines. This is not your typical menopause. In fact, the only evidence of moodiness is watching her toss hay at her uninterested mate.

This is gorilla menopause – the subject of a national study led by Brookfield Zoo and funded by the U.S. National Institutes of Health (NIH) National Institute on Aging, in hopes of learning more about the human female reproductive cycle.

Its cause is timely. By 2025 there will be an estimated 825 million women over age 65 – the largest-ever population of women simultaneously in menopause. The population of gorillas, which share many physical traits with humans, is mirroring these demographics in U.S. zoos, according to Brookfield Zoo research scientist and primatology specialist Dr. Sylvia Atsalis, who developed the study with Dr. Sue Margulis, former Brookfield Zoo behavioral research manager and now curator of primates at Lincoln Park Zoo. Like humans, gorillas in zoos are living longer than ever because of advances in scientific knowledge, nutrition and health care.

“The NIH was interested in our study because there’s a great deal of concern about maintaining the well-being of an aging human population,” says Dr. Atsalis. “As primates, humans and gorillas share many important physical traits. Our findings underscore those similarities and the parallel between humans and gorillas, our evolutionary cousins, who may be good models for an improved understanding of menopause.”

But the first question that the biologists faced was: do gorillas go through menopause?

The gorilla menopause study began as a pilot project at Brookfield Zoo when Dr. Atsalis and Dr. Margulis wondered whether Alpha, an elderly western lowland gorilla at the zoo, born in 1961, should be contracepted to prevent pregnancy. They feared that an animal of her advanced age would not be able to properly care for a baby -- conception is rare among gorillas in their late 30s. And yet Alpha was very interested in Ramar, the group’s silverback. Although she usually kept her distance, once a month Alpha would approach Ramar and stare at him intently, charged with desire, sometimes throwing hay and turning her back at him in a coy, sexual display. Alpha’s behavior would persist for a day or two, despite Ramar’s indifference. Then she would revert to her quiet and solo behavioral routine.

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Alpha tries to get Ramar's attention---he looks disinterested.
Alpha tries to get Ramar's attention.
Alpha tries to get Ramar's attention by tossing hay at him.
Alpha tries to get Ramar's attention by staring him down.
Alpha tries to get Ramar's attention by staring him down.
Alpha tries all the tricks in the book to get Ramar's attention; including a playful arm punch, tap, hay toss, and stare down.