Humans and other primates burn 50 percent fewer calories daily than other mammals, U.S. scientists say, explaining why we grow so slowly and live long lives.
Researchers at Chicago's Lincoln Park Zoo were part of a team of researchers in a study that examined the proposition primates' slow pace of life results from a slow metabolism, the zoo reported Wednesday.
Most mammals live a fast-paced life, reaching adulthood in a matter of months, reproducing prodigiously and dying in their teens if not well before.
In comparison, humans and our primate relatives have long childhoods, reproduce infrequently and live exceptionally long lives.
Working with primates in zoos, sanctuaries, and in the wild, the researchers used safe and non-invasive methods to measure the number of calories that primates burned in a 10-day period.
"The results were a real surprise," Herman Pontzer, an anthropologist at Hunter College in New York and the lead author of the study, said in a Lincoln Zoo release. "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 slow rates of growth, reproduction and aging among primates match their slow rate of energy expenditure, indicating evolution has acted on metabolic rate to shape primates' distinctly slow lives, the researchers said.
"The environmental conditions favoring reduced energy expenditures may hold a key to understanding why primates, including humans, evolved this slower pace of life," said study co-author David Raichlen, an anthropologist at the University of Arizona.
Linking growth, reproduction and aging to daily energy expenditure may shed light on the processes by which our bodies develop and age, the researchers said, and could improve our understanding of obesity and other metabolic diseases.
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