After about a year of pilot testing with Alpha and the zoo’s other older female gorilla, Beta (also born in 1961, during the human “Baby Boom”), and using the relative youngster Babs as a control (born in 1974), zoo scientists realized that they were onto a fruitful study – and one with potential implications for human health. They appealed to the NIH. Later that year, the NIH awarded them a grant to expand the inquiry nationwide. Brookfield Zoo enlisted the help of 16 zoos nationwide, which brought the number of gorilla study participants up to 30. Brookfield Zoo’s endocrinology lab remained the sole point of sample analysis from all gorillas, to ensure consistency of analysis and results.

The research team determined that about 25 percent of the older female gorilla population appears to be menopausal, meaning that their monthly hormonal cycles had ceased. Another 32 percent appears to be perimenopausal, which generally refers to a woman’s five to ten years before menopause, when the related physiological changes begin. Research confirmed that premenopausal subjects exhibited monthly sexual behavioral cycles that corresponded with regular hormonal fluctuations. During a regular two-to-three day monthly phase, the females were compelled to actively seek male attention, after which their interest dropped sharply until the next month’s episode.

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What struck Dr. Atsalis and Dr. Margulis was the fact that Alpha’s advanced age did not stop her sexual advances toward the male, which are typical of female gorillas. They wondered: are Alpha’s monthly advances toward Ramar associated with equally regular monthly cycles of progestogen, a reproductive hormone?

To find out, they enlisted the help of Dr. Nadja Wielebnowski, vice president of conservation science and a behavioral endocrinologist at Brookfield Zoo. Together, the scientists decided on the use of a non-invasive technique to track the hormonal cycles of the zoo’s female gorillas without disrupting their normal behavior. They relied on fecal samples to test the gorillas’ levels of progestogen, an already tried-and-true testing methodology but one that hadn’t before been applied to the study of menopause, says Dr. Wielebnowski.

Alpha Western Lowland Gorilla

Beta Gorilla Western Lowland Gorilla

“As long as there are hormonal cycles, even ‘senior citizen’ gorillas cycle sexually,” says Dr. Atsalis. It is fascinating to see how our data mirrors the human population. Some older females undergo menopause and others perimenopause, just like humans.”

The gorilla menopause study could not have been conducted in the wild or in zoos much before this time, the scientists say, because of increased longevity of gorillas and other animal species in the nation’s best zoos (Brookfield Zoo and others accredited by the American Zoo and Aquarium Association). As scientific knowledge and technology advance, so do the animal management skills and veterinary care that these zoos provide. Larger and more widely varied populations of animals in zoos, including endangered species, offer excellent naturalistic study opportunities.

“The collaboration between zoos was outstanding,” says Dr. Margulis. Extending the study enabled the scientists to include two of the nation’s oldest known female gorillas, Jenny at the Dallas Zoo (born in 1953) and Colo at the Columbus Zoo and Aquarium (born in 1956). “From what we found, there are very clearly menopausal females. This made sense to us but had never been confirmed. Many researchers in the field, however, were very surprised but glad to see it.”

The gorilla menopause study will be published in the December 2006 issue of the International Journal of Primatology.

Mysteries of Menopause
In addition to supplementing our understanding of physiological changes at menopause and how we might help human women and gorillas prevent osteoporosis, heart disease and other maladies linked to the onset of menopause, the gorilla research may help probe the numerous questions surrounding human menopause. Menopause is an issue of fervent and long-standing debate among anthropologists, according to Dr. Atsalis.

Along with humans, gorillas and a handful of other primates, there is only one other species that is known to have a lifespan that continues well past its reproductive years – the short-finned pilot whale. Why? Why have some animals evolved to live past their generative years but not others? What is the biological purpose of menopause? Why is there no equal point for men, at which their reproductive capacity unquestionably ceases?

Theories are rife, including the societal roles that both mothers and grandmothers can play long past their reproductive years, in terms of nurturing healthy offspring. There is also evidence of the valuable, social function of older individuals, as carriers of wisdom gained through experience.

“A zoo is a perfect setting for exploring these questions. Researchers are able to non-invasively extract data from consistent, documented social groups without making special arrangements,” says Dr. Atsalis. “All of the major health organizations would like to learn what they can about female aging because they are preparing to serve the health care needs of what will soon be the largest-ever concentration of menopausal women.” What’s more, she adds, the study’s result will better position zoos to provide even more informed care for aging gorillas.


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