The question arises as to how violence was born in man. Some other mammals had learnt it earlier. This is an unanswered question.
Man too is a social animal.
He lives in society together with other fellow beings. But social life by its very definition implies a life of inter-relatedness. These relations have multiple bases. To satisfy his sex instinct man built the institution of the family and new relations came into being. He made friends to indulge his feeling of affection.