Marxism's decline has been followed by a link up between evolutionary biology and social science which should produce startling insights into human behaviour, argue John Ashworth and Helena Cronin. At the hub of the dialogue have been seminars at the London School of Economics (below).

The dissolution of the USSR and the consequent worldwide repudiation of Marxist political systems has had momentous effects which are far from complete. But no less complete, and possibly even more far reaching, has been the collapse of Marxism as a philosophical system that claimed to provide a basis for most, if not all, of the social sciences.

Marx believed himself to be a scientist and his followers certainly thought of themselves as constructing a "science". Many of the habits of mind and attitudes thus created spilled over into the social sciences as they developed over the past century and were adopted more or less unconsciously by many of those who would rightly have rejected any attempt to label them as "Marxists". It is not proving easy to disentangle the useful and the helpful from the discredited in this complicated intellectual legacy and in the meantime there is a real hunger for something to take the place of the old framework. If classes, at least as defined in economic terms, and the class struggle no longer have the explanatory power that they once did, what might?

Into this debate have come, triumphantly, those from the political right with individualistic "there is no such thing as society" philosophies. More diffidently have come those from the "communitarian" or "new" left who are well aware of the lack of any real theoretical underpinnings to their pragmatic reworking of socialism. More tentative yet, are those who suggest that maybe modern evolutionary theories, which predict that organisms may apparently act "altruistically" while still containing "selfish" genes, can account for why both the political right and the "new" left seem to have only partial insights. Perhaps, the suggestion is, evolutionary theories might work where both individualistic and group (or class) based explanations of behaviour have failed.

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The tentativeness of the biologists would have been very familiar to Darwin whose illnesses might well have been partly caused by his all too conscious appreciation of the potential effect of his theories on human society. Indeed, at the end of the 19th century the premature application of Darwin's theory of natural selection by Herbert Spencer and others (all of whom misunderstood it) provided for some an apparently "scientific" basis for slavery, racial discrimination and other such notions which Darwin himself rejected with abhorrence. Worse, "survival of the fittest", a phrase Spencer, not Darwin, coined, was taken as a new justification for war, conquest and the physical elimination of those held to be "unfit". Here Spencer, a pacifist, was as horrified as Darwin would have been by the ends to which "Social Darwinism" was put, especially since G. E. Moore had shown conclusively in 1903 that the attempt to draw moral values from evolutionary theories was doomed from the start. But the damage had been done and most biologists and social scientists agreed to cease the dialogue that Spencer had started.

This self denying ordinance was tested a few times in the next 70 years or so. One of the real difficulties with Darwin's original hypothesis, which he well recognised, was that he had no secure theory of inheritance to account for the generation of the diversity among natural populations on which selection then operated. This problem was solved, at least in principle, by Mendel; and the combination of Mendelian genetics with Darwinian natural selection in the 1920s led to neo-Darwinism - an intellectually much more satisfactory theory. The application of neo-Darwinism to the social sciences was attempted more cautiously than in Spencer's time - not least because of the all-too-evident, then contemporary, political consequences of simplistic beliefs in the biological basis of human races.

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The social sciences were also better developed (not least thanks to Marx) and those developing them sensed, rightly, that the neo-Darwinist biologists were not yet in a position to contribute much of substance to any putative dialogue. Still there were some brave attempts, not least the establishment by William Beveridge, when director of the London School of Economics, of a chair in social biology to which Lancelot Hogben was appointed. The close contact thus engendered between some of the founding fathers of British social science and Hogben's toads (Xenopus laevis) created a fair amount of distaste and generated a certain amount of intellectual heat without shedding much light. The sad truth was that although neo-Darwinism was a better theory than Darwinism could ever have been it still lacked two key features - a satisfactory account of the evolution of behaviour, especially apparently altruistic behaviour on one hand and a description of the nature of genetic information.

Molecular biology and DNA, of course, now provide the latter while the solution to the first of these difficulties came, ironically, from the LSE through the work of a PhD student, William Hamilton, in the 1960s, though there is no evidence that any of his LSE contemporaries had any idea of the significance of what he was doing.

So, armed with a new Darwinian paradigm, should the evolutionary biologists and the social scientists try for a third time to see if they have anything fruitful to say to one another? The first attempts in the 1970s, under the banner of "sociobiology" by E. O. Wilson, were not encouraging. Wilson's self-confident and assertive tone was too reminiscent of Spencer's and many reacted, not to the new synthesis that Wilson was trying to popularise, but rather to the previous attempts of Spencer and the social biologists of the 1930s. The passions and antipathies raised by those previous attempts at dialogue were still so strong that few non-biologists stopped to notice that a new paradigm, not a rehash of the old ones, was being used. Most biologists, accepting the charges of insensitivity and tactlessness, opted to keep their heads down and few will now wish to be called sociobiologists. But under various descriptions such as "evolutionary psychology", "behavioural ecology" or "Darwinian anthropology" the implications of the new insights have gradually been explored and, more recently, in books such as The Red Queen by Matt Ridley and The Moral Animal by Robert Wright, accessible and sensitive accounts of the results have been published in a form that might lead to something other than a dialogue of the deaf.

Two different kinds of outcome might be expected from any such dialogue. The first is a change in emphasis, a shake of the intellectual kaleidoscope, as it were, rather than the addition of a new, brightly coloured, piece of knowledge. Such changes can be seen in many areas of medical research and health care and delivery with the introduction of the idea that it is necessary, to understand a phenomenon such as disease, to explain why and, if possible, how, it evolved. The notion that treating the symptoms of a disease such as fever might prolong the underlying cause has surprised many medical practitioners and similarly the idea that some apparent disorders like early morning sickness in pregnancy or mild anxiety might have (or have had) survival value may also lead to changes in the nature of treatments offered by medical practitioners. However, here, as in most other areas it would be foolish in the extreme to leap too readily from a plausible, not to say beguiling, evolutionary explanation to changes in practice. The development of "Darwinian Medicine", as the application of evolutionary thought to classical medical practice is called, is bound to be protracted since there is not yet any firm agreement on what are medically acceptable standards of evidence for the acceptance of an evolutionary explanation. To take a more everyday example: what could be more familiar than parent/offspring conflict? It is universal, has characteristic features, it seemsIwellI natural. But why does it happen? Robert Trivers, in the 1970s, showed that Darwinian theory provides a satisfactory answer. A parent must be judicious about the resources it puts in to an individual offspring. After all, any child carries only half of that parent's genes; and what is more only represents a fraction of the parent's total reproductive potential or opportunity. But from the child's point of view, it is far more precious and deserving of resources; after all, this is the only chance it will get. So there is an inherent, unavoidable imbalance in the parent/offspring relationship: it is inevitable that the offspring will always want more than the parent is prepared to give. We see this in the conflicts over weaning; in sibling jealousy; in attention-seeking tantrums etc. All very familiar and now all comprehensible.

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But as well as these changes of view on familiar problems, the shaking of the intellectual kaleidoscope, we should expect some brightly coloured bits of genuinely new knowledge. Typical of what should be expected are the startling insights provided by Martin Daly and Margo Wilson's studies on infanticide in the United States. Although conflict between parents and offspring is intrinsic, nevertheless altruism, love and solicitude are intrinsic too. After all, offspring and other close relatives are the only means any particular gene has of insinuating itself into future generations. It pays genes to make sure that those carrying them protect and care for those others who might also be carrying other copies of them - hence the Darwinian explanation of apparently "altruistic" behaviour. And yet sociologists have told us that the family is a dangerous place to be. The criminologists' statistics seem to support this. But, as Daly and Wilson showed, this is only true if a very un-Darwinian notion of the family is accepted. The likelihood of a child being killed by its parents is more than a hundred times greater when those parents are not biological kin - a socially appalling fact that had been obscured by the FBI's insistence on treating nonkin and kin alike in the homicide statistics. Infanticide is an extreme form of child abuse and, as we have come to realise, there is the same need in less extreme forms to keep a careful distinction between kin and non-kin. All those warnings about stepparents in fairy stories were well based in Darwinian theory. And much family violence is, of course, husband against wife who are not family in the Darwinian sense, and male and female mammals have very different, though both very rational in terms of genetic behaviour, reproductive strategies, another insight from evolutionary theory.

Indeed the list of those areas of social and cultural behaviour as well as medical practice where fruitful dialogue is happening or might be expected are growing rapidly: mate selection strategy; the nature and purpose of differences in male and female display techniques and hence the definition of "beauty"; crime and the way it is distributed among different genders and ages; language and how/why we have (over)developed it; the size of group with which we can associate or within which we feel comfortable; even why we have moral values and a (culturally very similar) sense of "natural" justice. The list is long and growing and we need to make sure that this time around the dialogue is indeed as productive as that list is long.

John Ashworth is chairman of the Board of the British Library. Helena Cronin is co-director of the centre for philosophy of the natural and social sciences, LSE.