Neuroanthropology has an all-too-brief interview on how different cultures around the world have fundamentally different ideas about what it means to be a friend.
The interviewee is anthropologist Dan Hruschka who has just written a book summarising his research on the anthropology of friendship.
It’s a wonderfully simple idea but really challenges some of our core assumptions about social relationships:
Can you describe one of your examples that really makes us think differently about friendship?
When you look at friendship cross-culturally, there are many surprises! Consider the fact that in societies around the world, close friends will sanctify their relationships with elaborate public ceremonies not unlike American weddings or that parents or elders can arrange their children’s friendships in much the same way that marriages are arranged in many parts of the world.
I think one of the more interesting findings, and one that reveals our own American preferences and taboos, concerns the kinds of things that friends are expected to help each other with. For example, in the U.S., we often expect friends to talk through personal problems and disclose deep secrets. Indeed, U.S. researchers often impose this criterion on definitions of friendship.
However, there are many places in the world where such verbal, emotional support is only a minor concern in friendships.
Link to Neuroanthropology on ‘the book of friendship’.
Mind Hacks 
There are unexpected physical expressions of friendship too. In some Islamic cultures men hold hands and link each other in a way that would be an unambiguous expression of homosexual relationships. Given the inherent homophobia in many Islamic cultures, influenced by religious belief, this seems a surprising outcome to many of us in the West.
It reminds me of of my university days in the seventies, when I was exposed to other cultures for the first time. Sat next to a friend from Algeria, he would often put his hand on one’s knee and squeeze – which initially freaked a few of us insular local students.