Orangutans are considered among the smartest of the great apes. The endangered animals live in Malaysia and Indonesia, spend most of their time foraging for food, and have an understanding of tools and speech. They are also not aggressive. But new evidence shows that their temperaments are not their only laid-back traits. The New York Times reports that orangutans have slow metabolisms — even slower than a human couch potato.

Scientists recently studied four orangutans that live in the Great Ape Trust, a nonprofit research lab in Des Moines, Iowa. The apes at this lab live much as they would in the wild, giving the biologists a close understanding of the animals’ true nature. The biologists are able to work with the apes through the use of rudimentary commands. In this experiment, the apes drank modified water and then urinated into cups. From that, the biologists measured how many calories the apes had burned.

Experts found that the great apes were burning very few relative calories, despite spending most of their time swinging from structures. This was unexpected, considering that sugary or fatty pulp fruits make up the majority of the animals’ diet. As the NY Times reports, Katy and Knobi, [two female orangutans] each weighing about 120 pounds, burned about 1,600 calories a day, several hundred less than a woman of similar weight who is getting moderate amounts of exercise.”

Herman Pontzer is a professor of biological anthropology at Washington University in St. Louis and lead author of the study. He told the NY Times that the apes may have developed this low metabolism to better handle times of starvation. Ultimately, it seems this trick of nature was developed to help the orangutans survive. Unfortunately, it may not ward off their ultimate extinction.

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