"While you may have no choice about the family you have, you can at least choose your friends. We and others have found that friendships tend to be characterised by similarity in likes and dislikes, known technically as homophily (love of similarity). It seems that the more things we have in common with someone, the closer the friendship will be. In our study, we identified five key traits that seemed to be particularly potent in creating friendships: having the same sense of humour, the same hobbies/interests, and the same moral values, having a similar level of education/intelligence, and having being born in (or, at least grown up in) the same area. The more of these five traits you share with someone, the greater is your emotional closeness to them, and the more likely you are to help them out in time of need."
Robin Dunbar, The Science of Love and Betrayal