Before the 21st century is upon us, we should bury deeply and for ever the issue that has shaped and sullied all 20th-century attempts to understand ourselves and to create a better society: that of "nature versus nurture". In the past 100 years this "debate" has run through sociology, psychology, anthropology and educational theory, and taken us to the furthest and most horrendous extremes of politics, from the gas chambers to the gulags.
Yet the debate is fatuous. Two books published in the last few weeks - Matt Ridley's Genome (Fourth Estate, £18.99) and Peter Singer's Darwinism Today (Weidenfeld and Nicolson, £5.99) - show how barren it has been. If we put the nonsense behind us then we might at last get some handle on the issue that exercised David Hume 200 years ago: "What is truly the nature of human nature?" When once we understand ourselves, we might at last begin to create societies that are benign (and indeed to see more clearly what benignity implies) yet also robust, and ways of living that are truly social yet also in tune with our personal needs and predilections.
The "nature" school is rooted partly in "biometrics", the attempt to measure all aspects of humanity - mental as well as physical - which was begun in the late 19th century by Francis Galton, and partly in genetics, which really began in 1900 when Gregor Mendel's research of the 1860s was rediscovered. Out of these disciplines came the idea that each of us is as we are because of our chance apportionment of genes - and with that came fatalism because, it was supposed, whatever was in our genes we couldn't do a damn thing about. Galton himself coined the term "eugenics" - the idea that we could make better human beings (stronger, cleverer and morally superior) by breeding them, just as we breed more compliant spaniels and toothier Dobermans. Intellectuals of all hues embraced this notion eagerly in the early 20th century - not least the socialists who, as Ridley somewhat gleefully points out, welcomed the thought that the state should take control of people's lives. The intellectuals changed their minds in droves, though, when the Nazis showed how very nasty such a scheme could really be.
The "nurture" school might trace its roots to the 17th century and John Locke, who said that the human mind at birth was a tabula rasa: a clean slate for life to write upon. This notion took many forms in the 19th and 20th centuries. Sigmund Freud felt we were shaped by our upbringing. Margaret Mead, from her conversations with the apparently free-spirited young women of Samoa, concluded that human morals were, in effect, infinitely flexible. Educationists of many schools took it to be self-evident that their ministrations were all-important. Sociologists in general have taken the tabula rasa as a given (and perhaps it is safer to do that than to begin with some more specific "model" that might be false). Karl Marx left a legacy that said (as quoted by Singer): "It is not the consciousness of men that determines their being but . . . their social being that determines their consciousness." Common sense and simple human kindness said that the environment must make a huge difference. Extreme socialist governments took it to be the case that human beings can be moulded any way we want; we can define the society first, and slot the people in accordingly. The history of the USSR (the corruption, the black market, the despair of workers and the apathy of middle managers) suggests that this is not quite the case.
Each "side" parodied and misconstrued the other - and still does, anachronistically. To each, the other is pig-headed and wicked in roughly equal measure. The "nurture" school accuses the "nature" school of "genetic determinism": of supposing that our genes effectively prescribe our lives and thoughts, so that we have no free will and hence no responsibility, and are stuck with whatever shortcomings (of intellect, physique or probity) that fickle nature has handed out to us. For good measure, the "nature" school is also held to be ineluctably right-wing. After all, we have the genes we have because that is what natural selection has left us with. Natural selection favours "the survival of the fittest" and, as Tennyson said, nature is "red in tooth and claw", so it seems to follow that natural selection must have favoured genes that prompt us to keep our fellows firmly in their place and biff them when necessary. If our genes really are affecting our thoughts and behaviour, then, say the nurturists, we had better make sure we keep them under wraps.
The "nature" school in general has more science on its side and accuses the "nurture" enthusiasts of knuckle- headedness and wishful thinking, while pointing out that the road to hell is paved with good intentions. Thus Freud's therapies flow beautifully from his crafted theories but the statistics suggest they don't actually work. Mead got it wrong: the bright young innocents of Samoa spun some fine tales, while sending her up rotten. There are many contrasting theories of education and schools of sociology and they cannot all be right. There is no progress in these fields - there are merely shifts of fashion. But if you assume that human minds are indeed blank slates which will record any message as complaisantly as any other, what progress can there possibly be?
A plague on all parodists. In truth, as Ridley so clearly describes, the notion that genes underpin behaviour has no connotations of "determinism". Genes in general suggest options: "If A happens, do X; if B, then Y." Neither are we stuck with what our genes predispose us to. Some genes increase our risk of heart disease: but if we know this and eat less fat, we reduce the risk. So environment is crucial. Furthermore, "genes make brains"; and brains, once made, can override the sotto voce urgings of the genes (especially if they understand what the genes are whispering to them). Free will is not threatened. It remains an essential concept. In general, genes, brains and environment operate in non-stop dialogue from the womb to the grave.
Neither are our genes innately right-wing. Ridley is right-wing, as it happens - but only in the patrician sense that he advocates individual freedom. But, as Singer argues, Darwinians can perfectly well be socialists. For Tennyson got it wrong, as Darwin knew full well: animals do not survive only by bashing each other. Modern evolutionary theory emphasises the many ways in which natural selection can favour co-operation and indeed "altruism". Oddly, it is because genes themselves are "selfish", as Richard Dawkins put it, that we can, as individuals, be unselfish. Our genes will happily sacrifice the creature that carries them if, by so doing, they become more widely spread.
More broadly, we have evolved as social creatures and as such we need each other; and natural selection will in general favour those who work together most harmoniously (though we must always be alert to cheats). Overall, as the Oxford zoologist Bill Hamilton has said, our genes form a "parliament", with some pulling one way and some another. Each of us is both competitive and co-operative. Circumstance largely determines which tendency prevails at any one time - that and our free will - just as the "nurture" school has argued all along.
But if our genes respond to the environment as flexibly as this, why are they important? Why not accept that, in effect, they do make each of us a tabula rasa? Because they, and we, are not infinitely flexible. Largely because of our genes, we have our limits and our predilections. The tabula is not rasa, but landscaped. We cannot be shoved into any hole that any political philosopher might choose to dig for us. We need to know which holes we might find amenable, and which not. Thus human beings do not work solely for personal wealth, as crude capitalism supposes, and to suppose that we do is to mistake our nature. But as social primates we do need reward and status, and will not work with any zest if all we can hope for is a safe apartment in a Stalinist block and a letter of commendation from a bureaucrat.
If we want to make societies that can endure and economies that truly bring us what we desire, then we have to build them in ways that acknowledge how we really are and what motivates us. To do this we must recognise that there is such a thing as human nature, explore what this implies and discover the circumstances that will bring out the best in us. Evolutionary and genetic theory have an essential part to play - not in telling us how we ought to be but in revealing the kind of creatures we are: creatures that our moral and political theory should be striving to assist. David Hume would surely have approved. This, after all, is an exercise in Enlightenment.
Colin Tudge is a research fellow in the Centre for Philosophy at the London School of Economics