A study published January 14, 2014 in the Proceedings of the National Academy of Sciences suggests that humans and other primates burn 50% fewer calories each day than other mammals of similar size. This slow metabolism, the researchers say, may help explain why humans and other primates grow up slower and live longer than most mammals.

An international team of scientists examined 17 primate species in zoos, sanctuaries and in the wild. Using a safe and non-invasive technique, they measured the number of calories the primates burned over a 10-day period. Herman Pontzer,Associate Professor of Anthropology at Hunter College, led the study. Pontzer said:

The results were a real surprise. Humans, chimpanzees, baboons and other primates expend only half the calories we’d expect for a mammal.