RECIPROCITY RULES
Oliver: I remember you!
Grocer: And I remember you too. Now get out of my store and stay out!
Oliver: Oh, don’t be like that. Let bygones be bygones. Let’s help each other. You have a business, and we have a business. We’ll send people to your store, and you send people to our store. What do you say?
Grocer: You mind your business and I’ll mind my business. Now get out before I throw you out!
—Laurel and Hardy in Tit for Tat
One way to determine which examples of direct reciprocity are real is to think about the qualities that are necessary for this mechanism to work. The evolution of cooperation by direct reciprocity requires that players recognize their present partner and remember the outcome of previous encounters with him or her. They need some memory to remember what another creature has done to them, and a little bit of brainpower to figure out whether to reciprocate. In other words, direct reciprocity requires reasonably advanced cognitive abilities.
I am sure that enough cognitive capacity is available in certain species of birds and among our closer relatives, most certainly the great apes. I am certain there is enough grey matter when it comes to human beings. If Harry does Fred a favor, Fred can remember what Harry looks like. He can also remember his good deed and how Harry has behaved in the past. Fred certainly has sufficient cognitive capacity to figure out from what he can remember if Harry is trustworthy and then tailor his behavior accordingly.
When it comes to the soap opera of everyday life, examples of direct reciprocity are everywhere. The running of a household depends on a ceaseless, mostly unconscious bartering of goods and services. In the kitchen, the one who cooks is often spared the drudgery of the washing up and vice versa. The concord among the members of a student house depends on everyone contributing equitably to cleaning duties, a food kitty, or whatever. If a friend helps us to move house, there is an obligation on us to help to pack his furniture when it is time for him to move, or unpack his crates. Families often harbor expectations that children will reciprocate for the care they receive as babies and as children by looking after their elderly parents.
When we receive invitations to dinner, a night at the theater, and so on, there comes an unwritten obligation to reciprocate in some way, in kind or with a treat in return. If a colleague at work hands you a gift-wrapped present, you make a mental note to reciprocate when her birthday comes around. When someone holds open a door, or gestures toward the mountain of food in a buffet, and says, “After you,” many instantly reply, “No, you go first.” The same sense of duty to reciprocate helps to make the ritual gift giving at Christmas expensive. And it can be found in bigger tribes and groups of people: businesses may have long-term contractual obligations with each other; governments make treaties with one another; and so on and so forth.
We repay meanness in the same coin. This is best reflected in the phrase “an eye for an eye, a tooth for a tooth,” from Exodus 21:24–27, in which a person who has taken the eye of another in a fight is instructed to give equitable recompense—his own. In the code of Hammurabi, created by an ancient Babylonian king, the principle of reciprocity is expressed in exactly the same way (“If a man put out the eye of another man, his eye shall be put out” and “If a man knocks the teeth out of another man, his own teeth will be knocked out”). One can see the same tit-for-tat logic in the idea of a “just war,” where the methods used to prosecute a conflict are proportionate to a given threat.
Unsurprisingly, given its central role in human life, reciprocity has inspired comedy. The vintage duo Laurel and Hardy used acts of slapstick revenge to give their movies a satisfying climax. One of their short films released in 1935 revolves entirely around reciprocal retaliations. Appropriately enough, the film is titled Tit for Tat.
So there’s plenty of evidence that we live in a reciprocating world. But, of course, it does not always follow that another player in the game of life will reciprocate. Because there is a cost involved in helping another, cooperation always comes with the threat of exploitation. Why should anyone share in hard work or return a favor? Why not cheat? Why not let the other guy toil and sweat, so you can reap the rewards of his hard work and not bother to do a similar favor? In fact, why do we bother with helping others at all?
After all, natural selection puts a premium on passing genes to future generations, and how can it shape a behavior that is “altruistic” in the long term when defection offers such tempting short-term rewards? In modern society, a hefty apparatus of law and order ensures that this temptation to cheat will remain, in general, resistible. But how can direct reciprocity work in the absence of authoritarian institutions? Why, in the case of cleaning stations on the reef, do clients refrain from eating their helpful cleaners after the little fish have discharged their duties?
This issue has been discussed for decades but, from the perspective of my field, was first framed the right way in a paper by Robert Trivers, an American evolutionary biologist. A fascinating character, Trivers, who suffers from bipolar disorder, became steeped in controversy because of his friendship with the leader of the Black Panther Party, Huey Newton. Today, at Rutgers, the State University of New Jersey, he specializes in the study of symmetry in human beings, “especially Jamaican.” Steven Pinker hails Trivers as one of the greats in western intellectual history.
One of the reasons Pinker rates him so highly is a milestone paper that Trivers published in The Quarterly Review of Biology in 1971, inspired by a visit to Africa, where he had studied baboons. In “The Evolution of Reciprocal Altruism” Trivers highlighted the conundrum of cheats by borrowing a well-known metaphor from game theory. He showed how the conflict between what is beneficial from an individual’s point of view and what is beneficial from the collective’s point of view can be encapsulated in the Prisoner’s Dilemma. As I explained in the last chapter, it is a powerful mathematical metaphor to sum up how defection can undermine cooperation.
At that time, Trivers did not refer to direct reciprocity but used the term “reciprocal altruism,” where altruism is an unselfish concern for the welfare of others. Although altruism is the opposite of the “selfish” behavior that underpins the more traditional view of evolution, it comes loaded with baggage when it comes to underlying motive. Over the course of this book I hope it will become clear that, although it seems paradoxical, “altruistic” behavior can emerge as a direct consequence of the “selfish” motives of a rational player.
Among the mechanisms to escape from the clutches of the Prisoner’s Dilemma, the most obvious one, as I have already hinted, is simply to repeat the game. That is why cooperation by direct reciprocity works best within a long-lived community. In many sorts of society, the same two individuals have an opportunity to interact not once but frequently in the village pub, workplace, or indeed the coral reef. A person will think twice about defecting if it makes his co-player decide to defect on the next occasion, and vice versa. The same goes for a fish.
Trivers was the first to establish the importance of the repeated—also known as the iterated—Prisoner’s Dilemma for biology, so that in a series of encounters between animals, cooperation is able to emerge. He cited examples such as the cleaner fish and the warning cries of birds. What is remarkable is that Trivers went further than this. He discussed how “each individual human is seen as possessing altruistic and cheating tendencies,”