Study finds primates age gracefully

A new study says chimps, gorillas and other primates grow old gracefully much like humans. The findings come from the first-ever multi-species comparison of primate ageing patterns reported in the March 11 issue of Science.

It was long thought that humans, who have relatively long life spans, age more slowly than other animals. But new research funded by the National Science Foundation's Division of Environmental Biology suggests the pace of human ageing may not be so unique after all.

We had good reason to think human ageing was unique, said co-author Anne Bronikowski of Iowa State University. Humans, for example, live longer than many animals with some exceptions - parrots, seabirds, clams and tortoises. But humans are the longest-lived primates.

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

Bronikowski is one of 11 biologists and anthropologists whose research figured into the study.

'There's been this argument in the scientific literature for a long time that human ageing was unique, but we didn't have data on ageing in wild primates besides chimps until recently,' said another co-author Susan Alberts, a Duke University biologist.

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 work focused on the risk of dying. When researchers 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 write in Science.

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,' said 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 say.

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 said. She is also the associate director of the NSF-funded National Evolutionary Synthesis Centre in Durham, N.C.

'Some human studies suggest we might be able to live a lot longer than we do now,' she said. 'Looking to other primates to understand where we are and aren't flexible in our ageing will help answer that question.'