A study done on chimpanzees in Uganda has found that they tend to form friend groups just like humans. The study has also shown that the chimps with close friends tend to have a lower stress level. Cortisol levels in urine were lower when chimps were observed performing everyday tasks with their closer friends than when they performed them with others they didn’t regularly associate with. With chimps being the closest living relative to humans, this study may shape the future of human medicine and therapy in regards to stress.

Chimpanzees need friends too — their stress levels show it – Los Angeles Times