Humans live longer than other mammals because of slow metabolic rate

A new study has shown that humans and other primates burn 50 percent fewer calories each day than other mammals, suggesting that these remarkably slow metabolisms explain why humans and other primates grow up so slowly and live such long lives.

The study also reports that primates in zoos expend as much energy as those in the wild, suggesting that physical activity may have less of an impact on daily energy expenditure than is often thought.

An international team of scientists working with primates in zoos, sanctuaries, and in the wild examined daily energy expenditure in 17 primate species, from gorillas to mouse lemurs, to test whether primates' slow pace of life results from a slow metabolism.

Using a safe and non-invasive technique known as "doubly labeled water," which tracks the body's production of carbon dioxide, the researchers measured the number of calories that primates burned over a 10 day period.

Combining these measurements with similar data from other studies, the team compared daily energy expenditure among primates to that of other mammals.

"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," lead author of the study Herman Pontzer, an anthropologist at Hunter College in New York, said.

This dramatic reduction in metabolic rate, previously unknown for primates, accounts for their slow pace of life.

All organisms need energy to grow and reproduce, and energy expenditure can also contribute to aging. The slow rates of growth, reproduction, and aging among primates match their slow rate of energy expenditure, indicating that evolution has acted on metabolic rate to shape primates' distinctly slow lives.

The study was published in the Proceedings of the National Academy of Sciences.