Why humans hang together, naturally

How do we construct societies, in a world of selfish individuals? This might look like a question for politicians, philosophers or economists. In The Origins of Virtue it is Matt Ridley's brilliantly argued contention that the key to its solution lies in the realm of biology. Human society is not the newly minted product of logical minds pursuing rational goals, but the legacy of a long evolutionary past. Natural selection has equipped us with a tool-kit of specialised social instincts. It is these inbuilt aptitudes that have underwritten our cultural achievements; it is to them to which we must turn to understand the nature of our society.

The natural world provides endless examples of the power of natural selection to build physical solutions to engineering problems. Think of the intricacies of the eye, or the exquisite mimicry found among butterflies and flowers. But, as Ridley makes clear in the first few chapters of his book, selection is no less impressive as a social architect. Sweeping from genes, to cells, to individuals, to groups, he documents the resolution of one potential conflict after another. At every level in the hierarchy of life, independent entities with their own selfish evolutionary interests coalesce to form social units. Genes combine to run cells, cells combine to make bodies, and individuals combine to form groups and colonies. At each stage, latent conflict threatens, but rebellion is suppressed. The benefit lies in the potential for specialisation and the division of labour. Animal bodies are not homogeneous clumps of cells, but complex structures formed from specialised tissues and organs, each contributing to the welfare of the whole. Ant colonies, on a lesser scale, have divisions of labour between worker and soldier, nest worker and forager, builder and hygiene specialist. Ridley's grand survey should be enough to convince even the most sceptical reader that conflicts of interest and their resolution are the stuff of evolution. But, as the author admits, the society of the genes is a far cry from a society of humans.

Animal bodies and social insect colonies are families, bound together by common descent. Your cells share the same evolutionary interests, because they all carry the same complement of genes. That most are doomed to eventual extinction matters not at all, as long as a few eggs or sperm carry those genes into the next generation. Sterile honeybee workers give up their own chance of bearing young to labour in support of their queen, but only because she is their relative. In helping her, they help to pass on their own genes by proxy. By contrast, while we humans are no strangers to nepotism, we readily cooperate with nonrelatives, too, on a scale that dwarfs most animal groups. If human society is such an evolutionary oddity, can we really turn to natural selection for an understanding of the social contract? Ridley's answer is yes. No example of animal cooperation can rival the scale and complexity of human organisation. But lion prides, dolphin coalitions and chimpanzee troops do reveal basic means by which selfish individuals can coordinate their activities, even when they are unrelated to one another. In almost every case, it is reciprocity and (paradoxically) group conflict that prove to be the cement holding societies together. The exchange of favours and the building of reputations serve to convert selfless actions into selfish benefits. Generosity now can bring rewards later, in the form of mating success or alliances with erstwhile competitors. The need for mutual defence and the opportunity for communal plundering of mates or food puts the emphasis firmly on joint activity. A group that is torn by dissension and internal conflict must forgo these benefits, to the detriment of each individual member. Exchange and group conflict both lead selfish genes to favour sociality, purely for the individual rewards it brings.

Ridley deploys a wealth of intriguing examples from social anthropology to show that these same themes of exchange, reciprocity and group hostility emerge again and again in diverse human cultures. Eating food, and most especially meat, is almost always a communal activity. But while we are happy to share food with members of our own group, this generosity is far from universal. Though trade links together widely separated peoples, even among stone-age hunter gatherers, territoriality and xenophobia are depressingly familiar human traits. Equally, while people everywhere will carefully husband their own resources, they readily exploit common property with profligate and sometimes ruinous abandon. Ridley sees, in these human universals, evidence of a basic instinctual program inherited from our evolutionary ancestors. Our emotions - feelings of guilt, shame, gratitude and sympathy - were laid in place by natural selection. The seemingly confusing blend of altruism and generosity that goes to make up human nature is an expression of the same selective pressures that have shaped the behaviour of other primates.

Are the differences between human and animal societies then simply ones of scale? Or have the rules of the social game changed more fundamentally? At some point, surely, human nature must give way to human culture. Differences between animal societies reflect genetic changes, but human cultural diversity need have no such basis. It is interesting to speculate, with Ridley, that the human love of song and dance may have evolved because it facilitated group cohesion. But it would be extreme to suggest that cultural preferences for one musical scale or another are the product of natural selection. That we should feel guilt and gratitude may be determined by our genes, but what excites these feelings changes from one culture to the next. Human society, then, is not entirely a given, but something we ourselves can shape. In his final chapter, Ridley offers us a vision of a natural society, in harmony with our inherited social aptitudes (and inaptitudes). But how our social instincts should be dealt with, which propensities should be encouraged or suppressed, is something most readers will want to decide for themselves.

To conclude, Ridley's book offers us a deep insight into the way that selfish genes can forge social groups, and shows us that the formation of society is not merely a human challenge, but a recurring theme of evolution. With clarity and honesty he shows us that to solve the problems of society, we cannot afford to overlook the mental tools with which natural selection has equipped us. But while the origins of virtue and of society lie in our evolutionary past, the social contract is not written unalterably in our genes. It is one thing to ask how society can be built, and another to ask how it should be built. Here, we may look to our evolutionary origins for guidance, but not for an answer.

Rufus Johnstone is Royal Society university research fellow, department of zoology, University of Cambridge.