We've been exploring how human cooperation can get off the ground among Darwinian agents. Specifically, we noted that kin selection provides a psychological mechanism that can get harnessed and applied, with intentional commitment, to non-familials. A second source of cooperative behavior is reciprocity.

Reciprocity in human evolution was first mathematically modeled in 1971 by Robert Trivers in his famous article The evolution of reciprocal altruism. Since that time, lots of attention has been devoted to the dynamics of reciprocity, much of it coming from game theory (for more on game theory see my sidebar).

Trivers' paper focused initially on a simple question: Why do some animal species share food with non-familials? In a Darwinian and Malthusian world food-sharing with non-familials seems very odd. Yet food-sharing is ubiquitous in the animal kingdom. Why does this behavior thrive? Why share food with non-familials?

A part of Trivers' answer is simplicity itself: We discount surpluses.

The more I have of something the less valuable it is to me. Conversely, if I find myself in scarce supply of something (take FOOD for example) then the value of that something tends to soar. Think of the kid who has ten rare rookie cards of Superstar X trading with the kid with none of those cards.

The point is that when Darwinian agents encounter each other they find each other in various levels of need. Some are flush and others are going hungry. Now imagine that the one going hungry begs for food from the one with surplus (food begging is commonly seen in these exchanges). Given that the agent with the surplus can discount his/her surplus (sharing some food in no way jeopardizes filling themselves up), he/she is free to share. And many species of animals do.

But this still makes no Darwinian sense. Why not hoard the food and starve the non-familial competitor? The answer is that at some future time the tables will turn. Thus, if the agent with surplus today can give a little in the hopes of future payback then it seems to be a good investment (because it costs so little given the surplus).

The point here is that reciprocity is leveraging off of an asymmetry:

Surplus = Low Cost < Scarcity = High Cost

Thus, when we see "sharing" we see Low Cost transformed to High Cost. Which is simply to say that when I share with you out of my surplus it means very LITTLE to me but it means A LOT to you.

Thus, for very little cost I can create a huge impact upon you, a sense of "indebtedness" that, if I need it in the future, I can leverage into a favor. Sharing, then, becomes simply an investment in my own future. Building up IOUs that I can cash in if I need to in the future. Reciprocity is evolution's version of insurance.

I'm leaving a ton out of this discussion. I'm mainly focusing on the role of asymmetries of surplus in fueling "cooperation" in the animal kingdom. As we noticed with family values (i.e., kin selection) seemingly "cooperative" acts can be very self-interested. I help you do X. Later, I need a ride to the airport and I cash in that favor. My helpfulness can seem, at times, very self-interested.

I believe this is why the bible is so keen on focusing on giving out of scarcity. Giving out of surplus is, like kin selection, an evolved mental trait. As such, like kin selection, it is, at root, self-interested. Interestingly, then, we see the bible again highlight an explicitly non-Darwinian moral norm. In this case, giving out of scarcity. Compare and contrast:

Evolved Darwinian Psychology: Kin Selection = Devoting time, effort, and resources on genetic relations
Biblical Witness: "If you greet only your brothers, what are you doing more than others?"

Evolved Darwinian Psychology: Reciprocity = Giving out of surplus
Biblical Witness: "As he looked up, Jesus saw the rich putting their gifts into the temple treasury. He also saw a poor widow put in two very small copper coins. "I tell you the truth," he said, "this poor widow has put in more than all the others. All these people gave their gifts out of their wealth; but she out of her poverty put in all she had to live on."

Jesus was an amazing evolutionary psychologist. It is as if he had read the very latest literature on the subject and explicitly spoke to transcending the subtle but selfish grooves of human nature.