Humans, monkeys age the same way

DUKE / IOWA STATE (US) — The assumption that humans age more slowly than other animals may not be true. It seems all primates follow a similar pattern of getting older.

The findings are from the first multi-species comparison of human aging patterns with those in chimps, gorillas, and other primates. Findings appear in the March 11 issue of Science.

We had good reason to think human aging was unique, says co-author Anne Bronikowski, an associate professor at Iowa State University. For one, humans live longer than many animals. There are some exceptions—parrots, seabirds, clams, and tortoises can all outlive us—but humans stand out as the longest-lived primates.

“Humans live for many more years past our reproductive prime,” Bronikowski says. “If we were like other mammals, we would start dying fairly rapidly after we reach mid-life. But we don’t.”

The results also confirm a pattern observed in humans and elsewhere in the animal kingdom: As males age, they die sooner than their female counterparts. In primates, the mortality gap between males and females is narrowest for the species with the least amount of male-male aggression—a monkey called the muriqui—the researchers report.

“Muriquis are the only species in our sample in which males do not compete overtly with one another for access to mates,” says co-author Karen Strier, an anthropologist at the University of Wisconsin who has studied muriquis since 1982.
The results suggest the reason why males of other species die faster than females may be the stress and strain of competition, the authors note.

Aging in the wild
“There’s been this argument in the scientific literature for a long time that human aging was unique, but we didn’t have data on aging in wild primates besides chimps until recently,” says co-author Susan Alberts, a biologist at Duke University.

The researchers combined data from long-term studies of seven species of wild primates: capuchin monkeys from Costa Rica, muriqui monkeys from Brazil, baboons and blue monkeys from Kenya, chimpanzees from Tanzania, gorillas from Rwanda, and sifaka lemurs from Madagascar.

The team focused not on the inevitable decline in health or fertility that come with advancing age, but rather on the risk of dying. When they compared human aging rates—measured as the rate at which mortality risk increases with age—to similar data for nearly 3,000 individual monkeys, apes and lemurs, the human data fell neatly within the primate continuum.

“Human patterns are not strikingly different, even though wild primates experience sources of mortality from which humans may be protected,” the authors wrote in a letter to Science.

Do the findings have any practical implications for humans? Modern medicine is helping humans live longer than ever before, the researchers note.

“Yet we still don’t know what governs maximum life span,” Alberts says. “Some human studies suggest we might be able to live a lot longer than we do now. Looking to other primates to understand where we are and aren’t flexible in our aging will help answer that question.”

(Courtesy: National Evolutionary Synthesis Center)