The other main type of altruism for which we have a well-worked-out Darwinian rationale is reciprocal altruism ('You scratch my back and I'll scratch yours'). This theory, first introduced to evolutionary biology by Robert Trivers and often expressed in the mathematical language of game theory, does not depend upon shared genes. Indeed, it works just as well, probably even better, between members of widely different species, when it is often called symbiosis. The principle is the basis of all trade and barter in humans too. The hunter needs a spear and the smith wants meat. The asymmetry brokers a deal. The bee needs nectar and the flower needs pollinating. Flowers can't fly so they pay bees, in the currency of nectar, for the hire of their wings. Birds called honeyguides can find bees' nests but can't break into them. Honey badgers (ratels) can break into bees' nests, but lack wings with which to search for them. Honeyguides lead ratels (and sometimes men) to honey by a special enticing flight, used for no other purpose. Both sides benefit from the transaction. A crock of gold may lie under a large stone, too heavy for its discoverer to move. He enlists the help of others even though he then has to share the gold, because without their help he would get none. The living kingdoms are rich in such mutualistic relationships: buffaloes and oxpeckers, red tubular flowers and hummingbirds, groupers and cleaner wrasses, cows and their gut micro-organisms. Reciprocal altruism works because of asymmetries in needs and in capacities to meet them. That is why it works especially well between different species: the asymmetries are greater.
In humans, IOUs and money are devices that permit delays in the transactions. The parties to the trade don't hand over the goods simultaneously but can hold a debt over to the future, or even trade the debt on to others. As far as I know, no non-human animals in the wild have any direct equivalent of money. But memory of individual identity plays the same role more informally. Vampire bats learn which other individuals of their social group can be relied upon to pay their debts (in regurgitated blood) and which individuals cheat. Natural selection favours genes that predispose individuals, in relationships of asymmetric need and opportunity, to give when they can, and to solicit giving when they can't. It also favours tendencies to remember obligations, bear grudges, police exchange relationships and punish cheats who take, but don't give when their turn comes.
For there will always be cheats, and stable solutions to the game-theoretic conundrums of reciprocal altruism always involve an element of punishment of cheats. Mathematical theory allows two broad classes of stable solution to 'games' of this kind. 'Always be nasty' is stable in that, if everybody else is doing it, a single nice individual cannot do better. But there is another strategy which is also stable. ('Stable' means that, once it exceeds a critical frequency in the population, no alternative does better.) This is the strategy, 'Start out being nice, and give others the benefit of the doubt. Then repay good deeds with good, but avenge bad deeds.' In game theory language, this strategy (or family of related strategies) goes under various names, including Tit-for-Tat, Retaliator and Reciprocator. It is evolutionarily stable under some conditions in the sense that, given a population dominated by reciprocators, no single nasty individual, and no single unconditionally nice individual, will do better. There are other, more complicated variants of Tit-for-Tat which can in some circumstances do better.
I have mentioned kinship and reciprocation as the twin pillars of altruism in a Darwinian world, but there are secondary structures which rest atop those main pillars. Especially in human society, with language and gossip, reputation is important. One individual may have a reputation for kindness and generosity. Another individual may have a reputation for unreliability, for cheating and reneging on deals. Another may have a reputation for generosity when trust has been built up, but for ruthless punishment of cheating. The unadorned theory of reciprocal altruism expects animals of any species to base their behaviour upon unconscious responsiveness to such traits in their fellows. In human societies we add the power of language to spread reputations, usually in the form of gossip. You don't need to have suffered personally from X's failure to buy his round at the pub. You hear 'on the grapevine' that X is a tightwad, or - to add an ironic complication to the example - that Y is a terrible gossip. Reputation is important, and biologists can acknowledge a Darwinian survival value in not just being a good reciprocator but fostering a reputation as a good reciprocator too. Matt Ridley's The Origins of Virtue, as well as being a lucid account of the whole field of Darwinian morality, is especially good on reputation.*
* Reputation is not confined to humans. It has recently been shown to apply to one of the classic cases of reciprocal altruism in animals, the symbiotic relationship between small cleaner fish and their large fish clients. In an ingenious experiment, individual cleaner wrasse, Labroides dimidiatus, that had been observed by a would-be client to be diligent cleaners were more likely to be chosen by the client than rival Labroides that had been observed neglecting to clean. See R. Bshary and A. S. Grutter, 'Image scoring and cooperation in a cleaner fish mutualism', Nature 441, 22 June 2006, 975-8.
The Norwegian economist Thorstein Veblen and, in a rather different way, the Israeli zoologist Amotz Zahavi have added a further fascinating idea. Altruistic giving may be an advertisement of dominance or superiority. Anthropologists know it as the Potlatch Effect, named after the custom whereby rival chieftains of Pacific north-west tribes vie with each other in duels of ruinously generous feasts. In extreme cases, bouts of retaliatory entertaining continue until one side is reduced to penury, leaving the winner not much better off. Veblen's concept of 'conspicuous consumption' strikes a chord with many observers of the modern scene. Zahavi's contribution, unregarded by biologists for many years until vindicated by brilliant mathematical models from the theorist Alan Grafen, has been to provide an evolutionary version of the potlatch idea. Zahavi studies Arabian babblers, little brown birds who live in social groups and breed co-operatively. Like many small birds, babblers give warning cries, and they also donate food to each other. A standard Darwinian investigation of such altruistic acts would look, first, for reciprocation and kinship relationships among the birds. When a babbler feeds a companion, is it in the expectation of being fed at a later date? Or is the recipient of the favour a close genetic relative? Zahavi's interpretation is radically unexpected. Dominant babblers assert their dominance by feeding subordinates. To use the sort of anthropomorphic language Zahavi delights in, the dominant bird is saying the equivalent of, 'Look how superior I am to you, I can afford to give you food.' Or 'Look how superior I am, I can afford to make myself vulnerable to hawks by sitting on a high branch, acting as a sentinel to warn the rest of the flock feeding on the ground.' The observations of Zahavi and his colleagues suggest that babblers actively compete for the dangerous role of sentinel. And when a subordinate babbler attempts to offer food to a dominant individual, the apparent generosity is violently rebuffed. The essence of Zahavi's idea is that advertisements of superiority are authenticated by their cost. Only a genuinely superior individual can afford to advertise the fact by means of a costly gift. Individuals buy success, for example in attracting mates, through costly demonstrations of superiority, including ostentatious generosity and public-spirited risk-taking.
We now have four good Darwinian reasons for individuals to be altruistic, generous or 'moral' towards each other. First, there is the special case of genetic kinship. Second, there is reciprocation: the repayment of favours given, and the giving of favours in 'anticipation' of payback. Following on from this there is, third, the Darwinian benefit of acquiring a reputation for generosity and kindness. And fourth, if Zahavi is right, there is the particular additional benefit of conspicuous generosity as a way of buying unfakeably authentic advertising.
Through most of our prehistory, humans lived under conditions that would have strongly favoured the evolution of all four kinds of altruism. We lived in villages, or earlier in discrete roving bands like baboons, partially isolated from neighbouring bands or villages. Most
of your fellow band members would have been kin, more closely related to you than members of other bands - plenty of opportunities for kin altruism to evolve. And, whether kin or not, you would tend to meet the same individuals again and again throughout your life - ideal conditions for the evolution of reciprocal altruism. Those are also the ideal conditions for building a reputation for altruism, and the very same ideal conditions for advertising conspicuous generosity. By any or all of the four routes, genetic tendencies towards altruism would have been favoured in early humans. It is easy to see why our prehistoric ancestors would have been good to their own in-group but bad - to the point of xenophobia - towards other groups. But why - now that most of us live in big cities where we are no longer surrounded by kin, and where every day we meet individuals whom we are never going to meet again — why are we still so good to each other, even sometimes to others who might be thought to belong to an out-group?
It is important not to mis-state the reach of natural selection. Selection does not favour the evolution of a cognitive awareness of what is good for your genes. That awareness had to wait for the twentieth century to reach a cognitive level, and even now full understanding is confined to a minority of scientific specialists. What natural selection favours is rules of thumb, which work in practice to promote the genes that built them. Rules of thumb, by their nature, sometimes misfire. In a bird's brain, the rule 'Look after small squawking things in your nest, and drop food into their red gapes' typically has the effect of preserving the genes that built the rule, because the squawking, gaping objects in an adult bird's nest are normally its own offspring. The rule misfires if another baby bird somehow gets into the nest, a circumstance that is positively engineered by cuckoos. Could it be that our Good Samaritan urges are misfirings, analogous to the misfiring of a reed warbler's parental instincts when it works itself to the bone for a young cuckoo? An even closer analogy is the human urge to adopt a child. I must rush to add that 'misfiring' is intended only in a strictly Darwinian sense. It carries no suggestion of the pejorative.
The 'mistake' or 'by-product' idea, which I am espousing, works like this. Natural selection, in ancestral times when we lived in small and stable bands like baboons, programmed into our brains altruistic urges, alongside sexual urges, hunger urges, xenophobic urges and so on. An intelligent couple can read their Darwin and know that the ultimate reason for their sexual urges is procreation. They know that the woman cannot conceive because she is on the pill. Yet they find that their sexual desire is in no way diminished by the knowledge. Sexual desire is sexual desire and its force, in an individual's psychology, is independent of the ultimate Darwinian pressure that drove it. It is a strong urge which exists independently of its ultimate rationale.
I am suggesting that the same is true of the urge to kindness - to altruism, to generosity, to empathy, to pity. In ancestral times, we had the opportunity to be altruistic only towards close kin and potential reciprocators. Nowadays that restriction is no longer there, but the rule of thumb persists. Why would it not? It is just like sexual desire. We can no more help ourselves feeling pity when we see a weeping unfortunate (who is unrelated and unable to reciprocate) than we can help ourselves feeling lust for a member of the opposite sex (who may be infertile or otherwise unable to reproduce). Both are misfirings, Darwinian mistakes: blessed, precious mistakes.
Do not, for one moment, think of such Darwinizing as demeaning or reductive of the noble emotions of compassion and generosity. Nor of sexual desire. Sexual desire, when channelled through the conduits of linguistic culture, emerges as great poetry and drama: John Donne's love poems, say, or Romeo and Juliet. And of course the same thing happens with the misfired redirection of kin- and reciprocation-based compassion. Mercy to a debtor is, when seen out of context, as un-Darwinian as adopting someone else's child:
The quality of mercy is not strained.
It droppeth as the gentle rain from heaven
Upon the place beneath.
Sexual lust is the driving force behind a large proportion of human ambition and struggle, and much of it constitutes a misfiring. There is no reason why the same should not be true of the lust to be generous and compassionate, if this is the misfired consequence of ancestral village life. The best way for natural selection to build in both kinds of lust in ancestral times was to install rules of thumb in the brain. Those rules still influence us today, even where circumstances make them inappropriate to their original functions.
Such rules of thumb influence us still, not in a Calvinistically deterministic way but filtered through the civilizing influences of literature and custom, law and tradition - and, of course, religion. Just as the primitive brain rule of sexual lust passes through the filter of civilization to emerge in the love scenes of Romeo and Juliet, so primitive brain rules of us-versus-them vendetta emerge in the form of the running battles between Capulets and Montagues; while primitive brain rules of altruism and empathy end up in the misfiring that cheers us in the chastened reconciliation of Shakespeare's final scene.
A CASE STUDY IN THE ROOTS OF MORALITY
If our moral sense, like our sexual desire, is indeed rooted deep in our Darwinian past, predating religion, we should expect that research on the human mind would reveal some moral universals, crossing geographical and cultural barriers, and also, crucially, religious barriers. The Harvard biologist Marc Hauser, in his book Moral Minds: How Nature Designed our Universal Sense of Right and Wrong, has enlarged upon a fruitful line of thought experiments originally suggested by moral philosophers. Hauser's study will serve the additional purpose of introducing the way moral philosophers think. A hypothetical moral dilemma is posed, and the difficulty we experience in answering it tells us something about our sense of right and wrong. Where Hauser goes beyond the philosophers is that he actually does statistical surveys and psychological experiments, using questionnaires on the Internet, for example, to investigate the moral sense of real people. From the present point of view, the interesting thing is that most people come to the same decisions when faced with these dilemmas, and their agreement over the decisions themselves is stronger than their ability to articulate their reasons. This is what we should expect if we have a moral sense which is built into our brains, like our sexual instinct or our fear of heights or, as Hauser himself prefers to say, like our capacity for language (the details vary from culture to culture, but the underlying deep structure of grammar is universal). As we shall see, the way people respond to these moral tests, and their inability to articulate their reasons, seems largely independent of their religious beliefs or lack of them. The message of Hauser's book, to anticipate it in his own words, is this: 'Driving our moral judgments is a universal moral grammar, a faculty of the mind that evolved over millions of years to include a set of principles for building a range of possible moral systems. As with language, the principles that make up our moral grammar fly beneath the radar of our awareness.'
Typical of Hauser's moral dilemmas are variations on the theme of a runaway truck or 'trolley' on a railway line which threatens to kill a number of people. The simplest story imagines a person, Denise, standing by a set of points and in a position to divert the trolley onto a siding, thereby saving the lives of five people trapped on the main line ahead. Unfortunately there is a man trapped on the siding. But since he is only one, outnumbered by the five people trapped on the main track, most people agree that it is morally permissible, if not obligatory, for Denise to throw the switch and save the five by killing the one. We ignore hypothetical possibilities such as that the one man on the siding might be Beethoven, or a close friend.
Elaborations of the thought experiment present a series of increasingly teasing moral conundrums. What if the trolley can be stopped by dropping a large weight in its path from a bridge overhead? That's easy: obviously we must drop the weight. But what if the only large weight available is a very fat man sitting on the bridge, admiring the sunset? Almost everybody agrees that it is immoral to push the
fat man off the bridge, even though, from one point of view, the dilemma might seem parallel to Denise's, where throwing the switch kills one to save five. Most of us have a strong intuition that there is a crucial difference between the two cases, though we may not be able to articulate what it is.
Pushing the fat man off the bridge is reminiscent of another dilemma considered by Hauser. Five patients in a hospital are dying, each with a different organ failing. Each would be saved if a donor could be found for their particular faulty organ, but none is available. Then the surgeon notices that there is a healthy man in the waiting-room, all five of whose organs are in good working order and suitable for transplanting. In this case, almost nobody can be found who is prepared to say that the moral act is to kill the one to save the five.
As with the fat man on the bridge, the intuition that most of us share is that an innocent bystander should not suddenly be dragged into a bad situation and used for the sake of others without his consent. Immanuel Kant famously articulated the principle that a rational being should never be used as merely an unconsenting means to an end, even the end of benefiting others. This seems to provide the crucial difference between the case of the fat man on the bridge (or the man in the hospital waiting-room) and the man on Denise's siding. The fat man on the bridge is being positively used as the means to stop the runaway trolley. This clearly violates the Kantian principle. The person on the siding is not being used to save the lives of the five people on the line. It is the siding that is being used, and he just has the bad luck to be standing on it. But, when you put the distinction like that, why does it satisfy us? For Kant, it was a moral absolute. For Hauser it is built into us by our evolution.