The key to longevity is a slow metabolism rate, say scientists.
Humans and other primates burn 50 percent fewer calories each day than other mammals and due to their low metabolism rate, they have a longer life span, according to a paper published in the Proceedings of the National Academy of Sciences.
Overall, 17 primate species, such as humans, gorillas, and mouse lemurs were examined for the purpose of the study.
The international group of scientists who carried out the study worked with animals in zoos, sanctuaries in Africa, and in the wild.
Daily energy expenditure of the primates was calculated using a technique called "doubly labeled water," Herman Pontzer, an anthropologist at Hunter College in New York and the lead author of the study, told The Monitor.
Water contains hydrogen and oxygen. Some of the hydrogen and oxygen in the water were being replaced with their variants, also called isotopes, Dr. Pontzer says. After animals drink water, these isotopes would then act as tracers and their presence could be found in their urine. By determining the concentration of isotopes from the urine sample, Pontzer and his team determined how much carbon dioxide the body produced. Over a 10-day period, scientists measured the number of calories primates burned, says Pontzer.
Comparing the results of the experiment with similar data from other studies, the team compared daily energy expenditure among primates to that of other mammals, according to a press release by Chicago's Lincoln Park Zoo. Chimpanzees and gorillas from the zoo were examined for the study.
"The results were a real surprise," said Pontzer. "Humans, chimpanzees, baboons, and other primates expend only half the calories we'd expect for a mammal. To put that in perspective, a human – even someone with a very physically active lifestyle – would need to run a marathon each day just to approach the average daily energy expenditure of a mammal their size."
The findings present an alternative explanation and help to look at the slow life history of primates differently, Steve Ross, coauthor of the paper and the Director of the Lester E. Fisher Center for the Study and Conservation of Apes at Chicago's Lincoln Park Zoo, told The Monitor.
It was earlier believed that primates have a slow life history because they do not invest their energy in growth; instead they allocate energy towards development and maintenance of their brain, Dr. Ross says.
"The environmental conditions favoring reduced energy expenditures may hold a key to understanding why primates, including humans, evolved this slower pace of life," said David Raichlen, an anthropologist at the University of Arizona and a coauthor of the study in a press release by Chicago's Lincoln Park Zoo.
The study has major implications for understanding how evolution has shaped human metabolism and why human beings differ from their ancestors, says Pontzer. He added, "It can also help us to better understand obesity and other metabolic diseases."