Chimpanzees are very intelligent animals. Their social
interactions are as fascinating as other aspects of
their lives. Chimpanzees have been known to enforce
specific rules when it comes to social obligations.
So, when one chimpanzee gives another a hair grooming,
it expects one or a similar favor in return.
There is also other behavior which would lead someone
to recognize the fact that chimpanzees are our closest
relative. Studies of chimp food sharing has revealed
many interesting details.