With our clothing, high-rises, technology and more, we humans would seem to be animal kingdom outsiders, existing outside the norm. But despite all our advances, it turns out we age and die at the same rate as other primates.
The finding, published in the latest issue of Science, shows how strong our ties to chimpanzees, gorillas and other primates is and counters the long-held belief that, with our relatively long life spans and access to modern medicine, we age more slowly than other animals.
"We are making a conceptual point that humans are really very much more similar in their aging patterns to other primates than anyone had suspected before," co-author Susan Alberts, a professor of biology at Duke University, told Discovery News.
"Humans have been a bit of an enigma," added project leader Anne Bronikowski. "We live much longer than would be expected based on our body sizes, our morphology, our maturation rates, and our reproduction rates. When comparisons have been made between humans versus lab or domestic animals (such as horses, dogs, rats and mice) humans have had slower rates of aging than these other species."
But no one until now had previously brought together detailed datasets on aging and mortality for multiple wild-living primates, and compared those to data on humans.
Bronikowski, an associate professor in the Department of Ecology, Evolution and Organismal Biology at Iowa State University, and her colleagues combined data from long-term studies of humans and these 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.
All of these primates and humans, experience high infant mortality, followed by a period of low mortality during the juvenile stage and an extended period of increasing age-specific mortality during mid to late life. These patterns apply to many animals, however, so the researchers took their analysis of primates a step further by focusing on the initial mortality rate (IMR) and the rate at which the probability of dying increases with age.
"We found that human females cluster with gorillas in infant mortality, and that human females cluster with chimps, sifakas, baboons, and muriquis in their rate of aging, so human females are really right in there with other primates in these two measures," Bronikowski said.
Men, on the other hand, appear to age more slowly than males of primate species in the wild, but the differences are minimal, according to the scientists.
"There is no evidence there that would make a person say, 'Wow, human males look really unique in their aging patterns,'" Bronikowski continued. "Moreover, the human males share similar aging features with the females of other primate species in this study."
It's clear that two factors increase overall primate life expectancy.
"Being female and being in a species where male-male competition is less intense are both good for longevity apparently," Alberts said.
Co-author Karen Strier of the University of Wisconsin-Madison explained that muriquis were the only species in the sample in which males do not compete overtly with one another for access to mates. This seems to benefit muriqui males, which age more slowly than other male primates do and live longer than other monkeys.
Caleb Finch, a professor of gerontology at the Ethel Percy Andrus Gerontology Center, authored a paper published in 1990 that showed some monkeys have rates of aging as slow as humans do and that infant mortality can vary widely within populations.
"I am glad to see an expanded analysis which more fully documents the environmental influence on human and primate mortality during aging," he told Discovery News. "This and future studies are relevant to the future of human lifespans.