本文作者：小红猪小分队

Source：http://www.newscientist.com/article/mg21628901.700-homo-virtuous-the-evolution-of-good-and-evil.html?full=true

Might the same forces have driven the evolution of our best and worst natures?

A FEW years ago, I attended a conference on animal behaviour in Atlanta, Georgia. The end-of-meeting party included a trip to the zoo and while we roamed freely between the caged beasts the conference organisers conducted a whimsical poll to discover what animals people thought were the “best” and “worst”. As you might expect the nominations were eclectic, but one name cropped up more frequently than any other - Homo sapiens. More striking still, humans were equally likely to end up in the “best” and “worst” categories. Some respondents even chose humans for both.

There is no getting away from it: Homo sapiens is both the basest of animals and the most noble. Ours is a species capable of horrific cruelty, genocide, war, corruption and greed. Yet we can also be caring, kind, fair and philanthropic – more so than any other creature. What lies behind this dual nature?

Our capacity for good and evil has exercised philosophers from Plato and Aristotle to Jean-Jacques Rousseau and Thomas Hobbes, but today some of the most exciting ideas are coming from an understanding of our evolution. In recent years, researchers have addressed such thorny questions as: why would altruism evolve, how did human conscience emerge, why does it feel good to be nice, and what causes us to give in to prejudice and hatred? The potential power of these insights is intriguing. By understanding the kinds of environments that foster the saint rather than the sinner, we can try to create societies that promote our better nature. It’s not just a pipe dream. Some evolutionists are already putting their theories into practice.

The key to virtue is altruism. Anyone can do the right thing given enough incentive, but what distinguishes genuinely good deeds is their selfless nature – a rare phenomenon in the wild. Although colonial insects such as bees and ants can show an impressive level of self-sacrifice, the individuals are so closely related that helping others is tantamount to being selfish, at least in evolutionary terms, since it ensures the survival of their own genes. Relatedness can also explain why many birds, and some other animals, will help rear each other’s offspring. It is far harder to find generosity extending outside the family. Even our closest evolutionary cousin the chimpanzee is basically selfish, although in one experiment chimps displayed a small amount of altruism similar to that found in young children, being just as likely to pass an object to an unfamiliar chimp even if some physical exertion was required (PLoS Biology, vol 5, p e184). In a nice twist to our preconceptions, vampire bats offer one of the very few bona fide exceptions to the rule, sharing blood meals with their roost-mates (Nature, vol 308, p 181).

Yet humans do appear to behave selflessly. Since the 1980s behavioural economists have used games to assess our altruistic tendencies. First came the “ultimatum game”, wherein player A is given some money and told to split it with a second anonymous player B. If B accepts the split, both keep their share, if not, neither gets a cent. It is free money, so B should accept any amount no matter how small and A should offer as little as possible. But that is not what happens. Instead, in university labs around the world, the most common offer is 50 per cent, with an average of around 45 per cent. Even in a refined version of the experiment called the “dictator game”, where A can choose either to give half or 10 per cent and B has no option to reject, three quarters of people make the more generous offer. It would appear that humans are very nice (and not very logical).

But are we really? Generosity may flourish in the sanitised environment of the lab, but experience suggests that people behave somewhat differently in the messy maul of the real world. And, sure enough, the evidence for virtue is less convincing out there. In one study, collectors of sports cards offered dealers a fixed amount of money in exchange for their best card at that price. John List from the University of Chicago found that when the transactions were done under his watchful eye, dealers played fair, coming up with a card that was worth what the collector had offered. But when dealers were not told they were taking part in an experiment, many ripped off their customers. Such cheating was particularly rife when they were off their home turf, away from their day-to-day customers (Journal of Political Economy, vol 114, p 1).

Why be nice?

Anyone who considers humans to be the worst of animals will conclude that people behave well only if they think they are being watched, proving that there is no such thing as altruism. Another interpretation is that we simply need to redefine virtue in biological terms. After all, altruism cannot be without benefit for the do-gooder, otherwise it would not have evolved by natural selection in the first place. Working on this principle, evolutionary biologists have come up with a variety of explanations for human niceness.

The first possibility is rather disheartening. Traditional hunter-gatherer groups tend to consist of closely related individuals, with kin constituting around a quarter of the members (Science, vol 331, p 1286). Individuals who helped their close relatives ended up passing on more genes, including those pushing us to help our own flesh and blood. So, like bees in a hive, we have evolved strong nepotistic instincts and, by this argument, niceness to non-relatives is simply a case of overspill.

However, it takes time and energy to help others, so evolution would have favoured people who made fewer of these costly mistakes, unless the generosity provided benefits that outweighed the costs. Reciprocity might be one such reason to do right by others. It can explain the altruistic behaviour of vampire bats, for example: they starve to death after a couple of nights without a blood meal, so sharing with a roost-mate that is likely to return the favour is an obvious strategy to help them pull through tough periods. Humans live in groups, are highly dependent on others, and we remember who owes us a favour, so we are perfectly placed to benefit from reciprocal altruism. Indeed, it might explain why List’s sports-card dealers tended to play fairer on their home turf, where they are likely to bump into customers again.

It’s not just our immediate acquaintances we have to worry about when considering the judgemental eyes of others. Humans are incredibly nosy: we like nothing better than to watch those around us and then gossip about our insights to others. This is how reputations are made and destroyed – and reputations matter. Virtues such as generosity, fairness and conscientiousness are universally valued and people seen to display them are rewarded – others like these individuals, want to do business with them and are more sexually attracted to them. So a good reputation can boost your chances of survival and reproduction. Taking this to its logical conclusion,Christopher Boehm from the University of Southern California, Los Angeles,argues that over the course of evolution rumour and hearsay may have forced us to become more altruistic – albeit in a biological self-serving sort of way.

Besides offering benefits for the individual, altruism would also have determined the way groups competed over resources. Those that pulled together would have beaten groups whose individuals were more selfish, ensuring their survival. This “group selection” has been a controversial idea, but it is increasingly being accepted as an important driving force behind the evolution of altruism, says Edward O. Wilson at Harvard University.

So we have ended up nicer and more caring than chimps. Even so, our egoistic tendencies must still be far stronger than our altruistic ones – after all, natural selection helps those who help themselves. Indeed, by becoming more altruistic, we created an environment where the selfish can enjoy the benefits of cooperative living – be it a share of mammoth meat or an equitable banking system – without paying the costs. Of course, if everyone did this there would be no cooperative group to begin with. That’s the dilemma our Jekyll-and-Hyde nature creates, but humans have evolved a few strategies to discourage free riders.

One is our seemingly innate desire to punish those who step out of line. People playing the ultimatum game will often reject mean offers from their partners just to see the Scrooges suffer, even if it means they both lose the prize. In another version of the game, people will even pay their own money to see selfish players punished for their stinginess. In the real world we commonly use gossip, censure and ostracism to punish minor misdemeanours, while the police, courts and prisons impose sentences to discourage more serious crimes. And although our prehistoric ancestors would have lacked institutions to enforce their rules, Boehm believes they used capital punishment as the ultimate sanction against free riders, based on his discovery that many modern hunter-gatherer societies have the death penalty. If he is correct, punishment has made our species a little bit less evil by removing the most antisocial genes from the human gene pool.

Fear of being punished is not the only thing that keeps our inner egoists in check. Often we are virtuous simply because it feels right. “You cooperate because it’s a good thing to do,” says Herb Gintis at the Santa Fe Institute in New Mexico. He calls this “strong reciprocity” because we end up doing things that are not personally beneficial but will be good for society if everyone does them – things like voting and giving money to people in need. Gintis believes this urge is behind all moral acts. What generates it?

This is where conscience comes in – not the esoteric entity with religious connotations, but an evolved, subconscious risk calculator that helps us weigh up the pros and cons of different moral options. It works like this. We learn the complex social rules of our particular culture and they become linked in our brains with emotions such as pride and honour, shame and guilt, giving them moral significance. These are the scales upon which moral judgements are weighed, and they tip the balance in favour of virtue; vice may be in your better interests, but it is associated with negative emotions, whereas virtue prompts positive ones.

The pleasure we get from performing a good deed is probably induced by a cocktail of neurochemicals but one seems particularly important. Normally associated with feel-good activities such as sex and bonding, the link between oxytocin and morality was discovered a decade ago by Paul Zak at Claremont Graduate University in California. His experiments reveal, among other things, that people with more oxytocin are more generous and caring, and that our oxytocin level increases when someone puts trust in us. Zak describes oxytocin as “the key to moral behaviour”.

The mama-bear effect

So it would appear we have a neurobiological mechanism that tricks us into placing other people’s interests above our own. This makes us less selfish but, perversely, is also behind some of our most heinous behaviour. That’s because the flip side of niceness to members of one’s group is nastiness to outsiders. This xenophobia is underpinned by oxytocin too (Science, vol 328, p 1408) and is sometimes called the “mama-bear effect” because it mirrors a parent’s urge to defend her offspring against a threat. As a result, the very system that keeps people working for the good of others can promote atrocities such as racism, genocide and war.

One consequence of this evolved conscience is that our concepts of “good” and “evil” are not universally shared, but rooted in the values of our culture. Take fairness. In modern western cultures, we tend to equate it with equity – one for me and one for you – but other cultures have different ideas. When researchers took the ultimatum game to 15 traditional societies around the world, they found that the average offer of player A ranged from 15 per cent in one society to 58 per cent in another (New Scientist, 10 March 2001, p 38).

The fact that people adapt to the values of their culture makes morality a movable feast. What’s more we are all members of multiple cultures – from our closest family to the whole nation – so even an individual’s moral compass is not fixed. Undoubtedly, some people are more predisposed to virtue than others but in a toxic culture almost everyone is capable of evil, from bullying and corruption to torture and terrorism. On the plus side, the converse is also true: the right cultural context brings out the good in us. That may not seem like a revolutionary insight, but some people believe it could make the world a better place.

Perhaps the most prominent of them is David Sloan Wilson at Binghamton University in New York state. For the past few years he has been applying what we have learned about the evolution of morality to his home city. Like any city, Binghamton has neighbourhoods where antisocial behaviour is rife and others where people actively work to help each other. He has mapped these peaks and valleys of prosociality and found when people move neighbourhoods they adapt their behaviour to fit the local culture. This is exactly what you would expect, given the factors that influence our moral behaviour. “People may want to be prosocial but in an environment where others are not you lose out,” says Wilson. His conclusion is radical. “There’s no point trying to make individuals more prosocial, you need to increase the prosociality of the entire neighbourhood.”

That is exactly what Wilson is trying to do. One approach involves giving residents the opportunity to create parks on local wasteland. These serve both to improve the physical environment, which Wilson finds has a strong influence on moral behaviour, and provide a common goal to build cooperative communities. Another project aims to make the classroom more cooperative and appealing to underperforming students by implementing Nobel-prizewinning economist Elinor Ostrom’s principles of group cooperation. Wilson has also set up the world’s first evolutionary think tank, the Evolution Institute, to bring these ideas to policymakers worldwide.

Evolutionary insights underline the importance of other measures to promote virtuous cultures, too. One is to encourage transparency, since we know that being watched puts us on our best behaviour, if only to enhance our reputations. Also crucial is the rule of law, including swift and just punishment for non-compliance (New Scientist, 5 November 2011, p 42). Less obvious, but highlighted by the study of 15 traditional societies, is economic development. “Modern market economies promote freedom, dignity, tolerance and democracy,” says Gintis. Even globalisation presents an opportunity for good. People’s wider social and information networks mean that the boundaries between groups are breaking down, reducing our xenophobic tendencies.

It will be interesting to see how far evolutionary theory in action can bring out the best in us. What is not in doubt is that our worst side will remain. Evolution has made us both altruistic and selfish – good and evil – and we cannot be otherwise. “It’s impossible for us,” says Edward O. Wilson. “If virtue was the only evolutionary force we would be angelic robots.”

Kate Douglas is a feature editor with New Scientist