The debate about the causes of violence long predates the current furore; only the language in which it is cloaked changes. Two decades ago the focus was not genes but chromosomes, when it was claimed that there was a higher than expected prevalence of men carrying an extra Y chromosome among those incarcerated for violent crime. And at the turn of the 20th century, for the followers of Lombroso, it was physiognomy rather than genes which predicted criminality. Before the time of modern science, it was simpler still; it was sufficient to invoke original sin, or predestination.

And even if the extra Y has now gone the way of physiognomy and sin, predestination (albeit now spoken in a medicalised hush rather than a hellfire rant) still lies at the heart of the argument.

After all, there are only three types of explanation for any aspect of human behaviour; its origins must lie in our current social circumstances, or in our individual life history, or it is in some way rooted in our biology. Of course such explanations are not necessarily incompatible, but at any time the emphasis given to each seems to depend less on the state of "objective" scientific knowledge than on the sociopolitical zeitgeist. In the context of rising public concern about levels of violence, an ideology which stresses personal responsibility and denies even the correlation between poverty and ill-health is likely to reject the social in favour of the individual.

Hitherto, in Britain at least, the focus has been on personal life history; the impoverished rearing practices of single mothers or the laxly disciplined schooling of the 1960s. But in the United States even this explanation is being discarded in favour of a return to original biological sin; the fault, we are told, lies in our, or rather their genes.

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The argument was put most clearly in 1992 by the then director of the National Institutes for Mental Health, Frederick Goodwin, in his proposed Federal Violence Initiative. Noting that violence was concentrated in the US inner cities, and especially among blacks, who have, he argued, inherited a cocktail of genetic predispositions; to diabetes, to high blood pressure, and to violent crime, he argued for a research programme to investigate the genetic or congenital factors which predispose them to such violent and antisocial behaviour. A few years previously, the psychologist Richard Herrnstein co-authored with James Q. Wilson Crime and Human Nature, a massive tome, which also focused on the proposition that violent crime in the US is the prerogative of the poor and black and that its origins lie in failures in their biological constitution.

Now there are many obvious objections to such a proposal. Some point to the fact that these discussions always seem to focus on working-class crime; no one seems to study the heritability of the tendency to commit business fraud, or the biochemical correlates of wife-beating among middle-class men. Others worry about the complex and sometimes contradictory web of meanings involved in the very concept of violence. On the one hand the identical act, of a man picking up a gun and shooting another at close range, if sanctioned by the state in times of war becomes an act of heroism worthy of a medal, whereas if it is if carried out in the midst of a drugs deal in a Manchester pub it is a crime punishable by a long term of imprisonment. On the other hand, all sorts of different acts are lumped together; Cantona's attack on an abusive football fan, fights between demonstrators and police, the Russian bombing of Grozny merge as if one word, violence, fits them all and that hence their underlying causes are all the same.

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One prominently published and frequently cited piece of research links such distinct activities as arson, attempted rape and exhibitionism carried out by three generations of members of a Dutch family living in different parts of the country at different times, as all exemplars of aggressive behaviour which can be linked to a single gene marker. When the phenomena under study are so varied, ill-defined and socially labile, how can one possibly consider seeking meaningful biological explanations?

It is hard to imagine that if the research had referred to non-human animal behaviour, its methodology and conclusions would have gained scientific credence - the licence granted to conclusions concerning human behaviour is far wider than that accorded to other animals.

Goodwin's proposal led to charges of racism, and he has subsequently left the NIMH, but a modified version of the initiative targeted on inner-city areas, such as Chicago, is up and running, and estimated to cost some $400 million. Not surprisingly, psychologists and psychiatrists, geneticists and molecular biologists have looked longingly at this particular pork barrel. Last year I was telephoned urgently by a well known California-based therapist, just off to Washington to present a proposal to study biochemical and immunological "markers" in "violent, incarcerated criminals". Would I collaborate with him, he asked, in analysing serotonin levels in fluids derived from spinal taps? Serotonin is a neurotransmitter whose metabolism is affected by a number of well-known drugs, including as it happens, the now notorious Prozac. To say nothing of the ethics of performing this type of operation on a - literally - captive population, the thought that such a study might provide a causal explanation for the endemic violence of US society is just the sort of simple-mindedness that the Violence Initiative fosters.

Among child psychologists the key word has become "temperament". This nebulous property is, they claim, to a significant degree heritable. Jerome Kagan suggests that some 10 per cent of the infants he studied show, from a very early age, a tendency to shyness which in later life expresses itself as aggression. To bolster this deterministic argument, he reports that he finds an analogous pattern of behaviour in kittens which grow into aggressive cats.

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Adrian Raine and his colleagues have studied a cohort of Danish males, now aged in their mid-twenties, and shown that children with birth complications, products of unwanted pregnancies and failed abortions, and who are institutionalised during the first year of life, committed a disproportionate number of violent crimes (murder, rape, armed robbery), and concluded that "biological factors play some role in violent behaviour - and the role is not trivial." That children with such a desperate history become damaged and even criminal adults is an observation would scarcely surprise even the most socially deterministic criminologist; the inclusion criteria for his sample are likely to cluster with many other impoverished aspects of the growing child's life history. Most, however, would probably regard Raines conclusion as a leap of faith justified only by a commitment to biologistic thinking.

No biologist could doubt the premise that individual differences in genes and during development help shape a person's actions and distinguish how one person behaves in a given context from another, nor that a study of the mechanisms involved in these developmental processes is of great scientific interest. But that is neither the reason why nor the way in which violence research is being conducted. Rather, it is framed within a reductionist and determinist paradigm which seeks the causes of social problems in individual biology, fostered by a political philosophy - on both sides of the Atlantic - which rejoices in the privileges which come with inequalities in wealth and power and rejects steps to diminish them.

The rate of violent crime and of incarceration is higher in the US than in any other industrial country. Can it really be the case that there is something unique about the genotype of the US population which so dramatically predisposes it to violence?

Furthermore, rates of violence are not static; in both the US and the United Kingdom, violent crime has markedly increased in recent years - thus in the US the death rate among young males increased 154 per cent between 1985 and 1994. Such fluctuations between and within societies are quite incompatible with any genetic explanation. One of the keys to success in science is to identify the appropriate level of analysis at which to seek the determinants of complex phenomena. When the differentials between rich and poor are so great and widening, where the potential rewards of violence may be so great (and if large enough can even be socially sanctioned) - and especially where, as in the US, there are said to be more than 280 million handguns in private ownership, to look to biology to provide a determining explanation of what is going on is an expensive and foolish diversion. Steven Rose is professor of biology at the Open University. He is working on a book on biology and human freedom.

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