Darwinism has always been more than a mere scientific theory; from the very beginning it has been embroiled in religious and political polemics. Appeals to keep "fact" separate from "value" have been to no avail; any theory of human origins will inevitably present itself as a theory of human nature and of human destiny. Yet while most people agree that Darwinism has a more than purely scientific significance, there is no agreement over what this additional significance is. The most divergent points of view - political, economic and ethical - have all claimed Darwin as ancestor. There have been capitalist Darwinians, anarchist Darwinians and environmental Darwinians. Weidenfeld and Nicolson's series of pamphlets, Darwinism Today, introduces new voices to this merry Babel.

In one important respect, however, these "neo-Darwinians" all differ from their discredited social Darwinist ancestors. The social Darwinists treated the theory of natural evolution in a loose and metaphorical manner, as a prototype for the evolution of human society. Different social arrangements were justified on the grounds that they provided the best analogue, in human terms, of natural selection, from unbridled capitalism to thinkers of a more collectivist bent who defined the basic unit of Darwinian competition as the nation. Conflict between nations would promote the fittest, it was argued, though within each nation statism prevailed. It was in this form that social Darwinism was appropriated by fascism. Yet none of these extrapolations from Darwin has the slightest validity. Darwin's is a theory of natural, not of social evolution; the principles governing the two processes are entirely different. Realisation of this fact, as well as the odium attaching to anything associated with fascism, ensured that Darwinism was not mentioned outside scientific circles for almost 50 years.

It is a chastened Darwinism that now pokes its head back into social and political conversation. Its target is no longer the macrocosm of human society, but the microcosm of human psychology. It claims that evolution has shaped not only our bodies, but also our souls. Evolutionary theory can elucidate that oldest of riddles: what is human nature? It can isolate those features of the human psyche that remain constant through all historical and cultural change, and that constitute a permanent obstacle to all projects of social reconstruction. Neo-Darwinism is an ironic reversal of social Darwinism. The social Darwinists were impressed by the dynamic and mutable character of nature, and hoped to reproduce these qualities in human society. Neo-Darwinism emphasises the extreme slowness of evolutionary change, and the constraints it places on social initiative. Its political implications are conservative. The right has always applauded pig-headed human nature as the ultimate bulwark against the ambitions of the state, whereas for the Marxist left "human nature" is simply a term of bourgeois ideology, immortalising the status quo.

The two essays by Kingsley Browne and, in collaboration, Martin Daly and Margo Wilson, are best representative of neo-Darwinism's political tendency. Browne argues that the relative scarcity of women at the top levels of management is the result of innate differences of character between the sexes. Men are, on average, more competitive, risk-loving and single-minded, and these characteristics are not mere "cultural constructs" but the product of a complicated process of "sexual selection". Daly and Wilson point to statistics showing that children are over 100 times more likely to be killed or abused by a step-parent. This should come as no surprise to anyone versed in evolutionary theory, the fundamental premise of which is that all creatures strive to promote their own genes over and above those of their rivals. Male lions habitually kill their displaced rivals' offspring; the cruelty of human step-parents is a vestige of this primitive evolutionary trait. All three writers are scornful of the social science model of the postwar years, according to which sexual difference was a mere cultural prejudice, and parenting a "social role". Policies based on these assumptions, such as quotas for women or the encouragement of "diverse family forms", will be either futile or destructive.

The most striking thing about both pamphlets is the way in which complex scientific arguments support a conclusion of outstanding banality. It says something about our lack of intuitive self-knowledge that we require proof that men and women are different, or that natural parents are more loving than step-parents. But I suppose there is no harm in this; if banalities require the support of science to become intellectually respectable, let them have it. Economics - a discipline with many affinities to Darwinism - is essentially nothing more than an elaboration of banalities.

But if banalities become no less banal through acquiring a scientific foundation, they certainly become more arrogant. It is important not to let them swagger too complacently. All scientific theories are imperialistic, and the neo-Darwinists' avowal that it is not their intention to diminish human freedom does not quite allay my suspicion that this is precisely their intention. Darwinism can only draw attention to the similarities between the human and animal worlds; it is, by its nature, insensitive to the differences. Yet these differences are all-important. Humans inhabit a symbolic, not a natural universe. If we cannot directly transcend our natural inheritance, we can, through the use of language, configure it and reconfigure it indefinitely. The same natural trait can be described in an endless variety of ways, each one transforming its value and significance. The impulse that we call anorexia and treat as a disease was in the Middle Ages revered as the mortification of the flesh. Whichever interpretation we prefer, it is not for science to adjudicate. Our natural endowment is not the obstinate and intractable thing of Darwinian theory; it is a counter in an ever-changing game.

Browne's essay is insensitive to the ways in which human beings manipulate and pervert their natural legacy. There are differences between men and women, but it's almost impossible to say anything universally valid about those differences. Any words that we use to describe them will be our words, bearing our judgements and interpretations, so we can hardly avoid the error of elevating cultural types into natural kinds. This is precisely the error committed by psychologists Katherine and Kermit Hoyenga, quoted by Browne: "[Women's] concepts of self are centred more around relationships with others, whereas men's egoistic dominance means that their self-concepts are centred more around task performances and skills."

Any individual has the ability to use his natural endowment artfully, thereby negating its significance. Thence the old adage that a woman's strength is her weakness can be transformed into a source of power. Browne's portrait of women as nurturing and altruistic may very well be true as far as nature is concerned, but human intelligence can transform these qualities into a mask, under which lurks a will to power equal to any man's.

Browne, in common with all neo-Darwinists, is entirely insensitive to the human faculty of cunning. "Women care less about money, status and power than do men" proclaims the dust jacket. Rubbish! Women care just as much about all these things; it's merely that they employ less conspicuous means in their pursuit. Men pursue money, status and power directly; women pursue them through the intervening medium of men. Or at least, that was how it worked traditionally.

The social scientists of the 1950s and 1960s were certainly wrong to regard the human psyche as a tabula rasa. Neo-Darwinism has performed a useful service in resurrecting the banal truths of human nature from their grave. But it errs in supposing that we can lay human nature out on the dissecting table, as though it were an object of natural science. We will never be transparent to ourselves; language and intelligence render us opaque. Over and above the banal truths - men and women are different, parents love their children more than step-parents - we can say very little. And while human nature will continue to confound misguided schemes of social engineering, we will never know it well enough to derive from it any positive recommendation for action.