New research shows that humans and other primates² burn 50% fewer calories each day than other mammals. The study, published January 13 in the Proceedings³ of the National Academy of Sciences, suggests that these remarkably⁴ slow metabolisms⁵ explain why humans and other primates grow up so slowly and live such long lives. The study also reports that primates in zoos expend⁷（消耗） as much energy as those in the wild, suggesting that physical activity may have less of an impact on daily energy expenditure⁸ than is often thought. Most mammals, like the family dog or pet hamster（仓鼠）, live a fast-paced life, reaching adulthood⁹ in a matter of months, reproducing prodigiously¹⁰（巨大地） (if we let them), and dying in their teens if not well before. By comparison, humans and our primate¹ relatives (apes, monkeys, tarsiers, lorises, and lemurs) have long childhoods, reproduce infrequently, and live exceptionally long lives. Primates' slow pace of life has long puzzled biologists because the mechanisms¹¹ underlying¹² it were unknown.

 

An international team of scientists working with primates in zoos, sanctuaries¹³, and in the wild examined daily energy expenditure in 17 primate species, from gorillas¹⁴ to mouse lemurs, to test whether primates' slow pace of life results from a slow metabolism⁶. 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.

 

"The results were a real surprise," said Herman Pontzer, an anthropologist¹⁵ at Hunter College in New York and the lead author of the study. "Humans, chimpanzees, baboons¹⁶, 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 physically¹⁷ active lifestyle -- would need to run a marathon each day just to approach the average daily energy expenditure of a mammal their size."

 

This dramatic reduction in metabolic¹⁸ rate, previously¹⁹ 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 environmental conditions favoring reduced energy expenditures²⁰ may hold a key to understanding why primates, including humans, evolved this slower pace of life," said David Raichlen, an anthropologist（人类学家） at the University of Arizona and a coauthor of the study.

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