Costs and benefits changed depending on the size of gorilla groups, and differed for males and females. For example, friendly females in small groups didn't get ill very often but had fewer ...

Billy, the two-year-old gorilla, went head to head with a grown man to see who would come out on top. Billy, the two-year-old gorilla, went head to head with a grown man to see who would come out ...

The silverback mountain gorillas are an endangered species of primate found in Uganda, Rwanda and Congo. There are believed to be only 400 remaining in the wild. (Getty Images) ...