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Humans aren’t the only ones who grow old gracefully

March 10, 2011

A new study of primate aging patterns shows aging rates and mortality gender gap similar for human and non-human primates.

For a long time it was thought that humans, with our relatively long life spans and access to modern medicine, aged more slowly than other animals. Early comparisons with rats, mice, and other short-lived creatures confirmed the hunch. But now, the first-ever multi-species comparison of human aging patterns with those in chimps, gorillas, and other primates suggests the pace of human aging may not be so unique after all.

The findings appear in the March 11 issue of Science.

You don’t need to read obituaries or sell life insurance to know that death and disease become more common as we transition from middle to old age.

 “Long-term aging was thought to be unique to humans, primarily because most aging studies are done on short-lived animals like mice and fruit flies. But there may be things about our lives and that of other primates that may be quite different than short-lived animals,” says Dr. Linda Fedigan, co-author of the study and Canada Research Chair in Primatology and Bioanthropology at the University of Calgary, whose 28-year study of capuchin monkeys contributed to the data.

The study is the first to share research data across seven long-term studies of between twenty-five and fifty years on seven wild primate species. It includes data from Jane Goodall’s chimpanzee research site in Tanzania and Dian Fossey’s study of gorillas in Rwanda. Also included are data on capuchin monkeys from Costa Rica, muriqui monkeys from Brazil, baboons and blue monkeys from Kenya and sifaka lemurs from Madagascar.

The team focused not on the inevitable decline in health or fertility that comes 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.

“We examined patterns of mortality and mortality risk from infancy to adulthood and found that all the primates followed a pattern similar to that of humans where there are high mortality risks in infancy, which level off for juveniles and into early adulthood, and then increase again once individuals reach full adulthood,” says Fedigan.

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. The authors suggest the higher risk of death in males may be due to the stress of male competition.  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 where males are very non-aggressive and which does not compete for access to females,” says Fedigan. “They live in brotherhoods and are more collaborative with other males. They are not wounding each other or stressed due to fighting and competing.”

Do the findings have any practical implications for humans? Modern medicine is helping humans live longer than ever before, the researchers note. “We may not know yet what the maximum human life span is and there may be factors in our evolutionary history to help us understand,” says Fedigan. “The questions we can ask get better the longer we can study the life spans of primates. All we can go by is the longest reliable record we have right now.”