In the wake of the BBC's evolution weekend and the recent comments made by Richard Tilt about black people possibly being genetically "more likely" to die in custody, I have been recalling a conference I attended in 1990 for right wing politicians and academics organised by the Centre for Policy Studies

A keynote speaker was Richard Herrnstein who, with Charles Murray (a key proponent of the underclass theory) in 1994, was to publish a book arguing that blacks genetically inherit lower intelligence than whites.

Over a lavish lunch, surrounded by leading Tory politicians - including Keith Joseph, once the favourite for the Conservative leadership before "coming out" as a eugenicist - I quizzed Herrnstein about his opinion of the role of genes in causing poverty. He told me that "there are different genes for different classes". If 1,000 poor boys were swapped at birth with 1,000 rich boys would the parents notice? "The parents of the swapped boys in your experiment would start to realise they were different soon after birth."

The belief that the genes of the poor are the primary cause of their socio-economic status is at the very heart of the Right's thinking. What view does New Labour take? To the best of my knowledge, Frank Field MP was not present at the 1990 conference. But it is interesting that last month, the Centre for Policy Studies felt he was sufficiently likeminded to invite him to address them.

Field's rather abstract Green Paper on welfare reform, published last week, provided no clues to his underlying convictions about the role of genes in behaviour. But what they are will profoundly effect what he actually does - and for that matter, what Blair has in mind for education and health.

It is an undeniable fact that the poor are more prone than the rich to bad health, most mental illnesses, divorce, low scores on intelligence tests, low educational attainment and criminality. If the primary reason is their genes, so the Right's argument goes, then what is the point of spending vast sums of money on trying to improve them? The psychological sludge in any society will always fall to the bottom of the gene pool and no amount of well-intended water management can change that. No wonder that welfare programmes always fail. You would be as likely to change the colour of their eyes (or skin) by talking to them, as to make the poor cleverer by giving them extra education.

Confronted with this argument, most liberals are so overcome with indignation and disgust that they dismiss it out of hand. But that way bigotry lies. The scientific evidence for these ideas must be considered.

Studies of identical twins and of adopted children suggest that all manner of human behaviours have a genetic component. The most gung-ho interpreters of these studies claim that intelligence is at least half heritable, along with divorce and the major mental illnesses of depression and schizophrenia. Your occupational and educational achievements are respectively estimated to be 43 per cent and 51 per cent heritable. That many other personal traits, including violence, neurosis and minor depressions, emerge from the studies as having little or no heritability is rarely mentioned. Since nasty things generally happen more to poor people, if these estimates of heritability are right, it follows that poor people are more likely to have poor genes.

However, even if you accept the estimates at face value (and also overlook the large proportion of human behaviour which emerges from the studies as having little or no heritability), what they reveal is not the overwhelming power of genes in shaping us but the crucial role of the environment. If some behaviours are about half genetic, it still remains critical what the environment is like because that will determine how much these in- built propensities are expressed in practice.

In any case there are a large number of good reasons to suspect that the twin and adoption studies are badly flawed or even of dubious provenance. Take the most widely cited source for heritability estimates, Thomas Bouchard's group in Minnesota. He claims to have studied more than 200 pairs of identical twins who were separated in early childhood. You are almost bound to have come across his work in one of the uncritical television documentaries or newspaper articles devoted to it in the past few years.

What these media offerings never mention is that Bouchard's work was supported by New York's Pioneer Fund, to the tune of $1.3m. This foundation has its roots in the eugenics movement of the 1930s and a clue to its political leanings comes from the fact that it also funds research to establish the advantages of racial segregation. Nor do the media point out that Bouchard refuses to allow his critics to look at the raw material upon which his claims are based or to publish many crucial details necessary for its proper evaluation.

Given the unfortunate history of fraudulence in this field, the origins of Bouchard's research funds and his secretiveness are worrying. But the media do not seem to care. He has allowed eager, ignorant swarms of them access to selected twin case histories which they cheerfully use to illustrate his theories. None seems interested in looking more closely at his motives or scientific integrity.

The recent media gene-fest may have affected our political life. Drawing heavily on Bouchard's work, Lawrence Wright, probably the journalist to have made the most money out of this mini-industry, wrote this year that "as the views of the environmentalists lose favour, the politics that have been built on their assumptions crumble."

Is it possible that science caused the shift from old to New Labour, that Tony Blair and Frank Field have bowed to the "power of twin and adoption studies"? I doubt it very much. But busy politicians, who rarely read scientific papers at first hand, may have been encouraged by ill-informed media reports to believe we are substantially shaped by our genes and, therefore, that a large number of the population cannot be much helped by welfare programmes.

I do not know what either Blair or Field really believe about these matters but I do suspect that the lazy peddling of questionable studies by journalists and TV producers has created a climate in which genes are now generally accorded a far greater role in determining who we are than is merited by the evidence.

Oliver James's book `Britain on the Couch - Why We're Unhappier Compared with 1950 Despite Being Richer' is published by Century (pounds 16.99).