Friendship and Deep Engagement Relationships
Is there something more to friendship than reciprocity? Are some mates soulmates--people with whom you have a deep engagement relationship?
Tooby, J. & Cosmides, L. (1996). Friendship and the Bankerís Paradox: Other pathways to the evolution of adaptations for altruism. In W. G. Runciman, J. Maynard Smith, & R. I. M. Dunbar (Eds.), Evolution of Social Behaviour Patterns in Primates and Man. Proceedings of the British Academy, 88, 119-143. PDF
The banker's paradox is a metaphor for a common life situation among hunter-gatherers. When you desperately need a loan, the bank doesn't want to give you one because you are a bad credit risk. But when you are in good shape and don't really need a loan, the bank is happy to give you one. It is not a paradox for the banker of course, but for the person who is in need. In a world governed by reciprocation alone, how can one get help when one is in desperate ned and is therefore a bad "credit risk"?
In Friendship and the Banker's Paradox, we propose that there was selection for deep engagement relationships, with specific properties, as a form of insurance against times of desperate need.
Desperate need. For evidence that illness and injury severe enough to require extended provisioning by others is common among foraging people, see Sugiyama, 2004
Irreplaceability. When you are in desperate need, you are a bad "credit risk", and reciprocation partners will be better off abandoning you. But that is true only to the extent that the benefits they get from you they can get from others--to the extent you are replaceable. By becoming irreplaceable to a small number of others--close friends--they have a stake in your well-being, making it beneficial for them to help pull you through the times when you are in terrible need. The fact that these individuals are among the few in the world with a stake in your well-being gives you a stake in theirs, which gives them even more of a stake in yours, etc, in a way that can lead to a deep engagement relationship--a true friendship.
For evidence from foraging people of a desire to become irreplaceable to others by cultivating special and socially valued talents, see Sugiyama & Scalise Sugiyama, 2003.