Alpha, a 45-year-old lowland gorilla at Chicago's Brookfield Zoo, would be about 70 in human terms, but she continues to display such a robust libido that two worried zoo scientists launched a study four years ago to see whether she could still get pregnant.
To put it another way, they wanted to know: Do gorillas go through menopause?
While human females often live a third of their lives beyond their child-bearing years, science had thought that all other species are able to reproduce until they die. But the researchers at Brookfield Zoo and Lincoln Park Zoo (also in Chicago) have found otherwise in a study being published in the International Journal of Primatology.
Their discovery that some older gorillas are menopausal has implications for zoos, which could take some apes off birth control without fear of a risky pregnancy. But the researchers also hope the information may help unlock mysteries of human menopause, including how it evolved.
Proving that the rigors of scientific inquiry are not always glamorous, the study required cooperating ape keepers from zoos all over the country to meticulously collect droppings from certain gorilla females. They put green food coloring in the apes' snacks to produce easily identifiable green droppings, which keepers put on dry ice and shipped by overnight mail to Chicago to be analyzed for a key hormone.
Alpha, the gorilla who inspired this undertaking, is a mother of seven whose last baby was born in 1991. She continues to go into heat every month, which means for two days she vamps for Brookfield's male gorilla leader, Ramar.
"It's not uncommon for female gorillas to strut about, purse their lips and throw glances at the male to let him know they are in estrus and would be receptive to his attentions," said Sylvia Atsalis, a staff primatologist at Brookfield. "But Alpha is particularly unabashed in this regard."
Because Ramar seems most interested in younger females, her attempts often fail, perhaps leading her to try harder. She sits close to him and stares into his eyes. She throws hay in his face. She tries sitting in his lap and makes lewd gestures.
"I've seen them mate, but it is very rare and it is half-hearted on Ramar's part," Atsalis said. "Usually he just ignores her, and sometimes he gets so aggravated that he chases her away."
Dangerous pregnancy
