Friends With Benefits

Humans aren't the only species capable of forging true and lasting friendships. Animals do it too--and get many of the same rewards

Catherine Ledner for TIME

Since 1995, John Mitani, a primatologist at the University of Michigan, has been going to Uganda to study 160 chimpanzees that live in the forests of Kibale National Park. Seventeen years is a long time to spend watching wild animals, and after a while it's rare to see truly new behavior. That's why Mitani loves to tell the tale of a pair of older males in the Kibale group whom the researchers named Hare and Ellington.

Hare and Ellington weren't related, yet when they went on hunting trips with other males, they'd share prey with each other rather than compete for...