Tuesday Book: Gene wars - the Third Way

DESIGN FOR A LIFE: HOW BEHAVIOUR DEVELOPS BY PATRICK BATESON AND PAUL MARTIN, JONATHAN CAPE, pounds 19.99

SCIENTISTS HAVE left the simplistic nature-nurture dichotomy behind them. They agree that we are the products of subtle interactions between our genes and the circumstances in which those genes find themselves. They know that DNA specifies the structure of proteins, not behaviour.

The trouble is that these truths are affirmed both by those scientists who embrace the idea of "genes for" this and that, and by those who abhor it. Despite the lofty insistence in both camps that they have risen above the debate, the differences between the genes Roundheads and environment Cavaliers remain deeply entrenched. This state of affairs may be difficult to interpret for spectators, faced with polemics that appear to agree on basic principles. Design for a Life may well be the book that such innocent bystanders have been waiting for.

Any book that sports warm endorsements from Richard Dawkins and Steven Rose, arch-Roundhead and arch-Cavalier respectively, is remarkable enough in itself. Neither of those authorities would care much for a story without convictions, and nor do Patrick Bateson or Paul Martin. They write disdainfully of accounts that produce an "insipid compromise" between the camps, and reject the idea of kicking the problem into touch by invoking, in a phrase borrowed from Salman Rushdie, a P2C2E - a Process Too Complicated To Explain.

Yet as one's ear tunes in to the book's measured tones, not even a distant growl of axes being ground is audible. The only faction whose hackles are likely to rise is the blood sports lobby. It laid into Bateson (Cambridge's professor of ethology) after he wrote a report that concluded that stags suffer from being hunted.

Bateson and Martin offer developmental processes, both before and after birth, as a sort of Third Way to understand the relationship between genes and environment. Like other exponents of Third Ways, they favour a cocktail of ideas that are traditionally considered to clash.

They are comfortable with claims from evolutionary psychologists about the universality of aspects of beauty, such as the ratio between women's waist and hip sizes. When discussing the theory that differing genetic interests lead to struggles over resources between mother and foetus, they do not echo the critic who condemned it as an "outrageous" product of patriarchal assumptions. Their interest lies not in whether the theory leads to a commendable moral, but how well it models the processes that it seeks to explain.

The litmus test of attitudes to heredity is the question of intelligence. Bateson and Martin note that surveys of educational projects in the US that intended to redress the balance for disadvantaged children show that people who have been through such schemes do enjoy benefits in later life. However, these benefits are observed in dimensions other than intelligence, such as community- mindedness, emotional health, and staying on the right side of the law. Thus they favour liberal policy prescriptions, without contradicting the conservative theoretical position.

In other dimensions of inequality, a developmental perspective can cast a flattering light on low scores. So smallness tends to be regarded as the pathological outcome of deprivation. It may, however, be regarded as an adaptive response by which the developing organism cuts its cloth according to its likely means. Mothers may supply their unborn offspring with a "weather forecast" based on their own experience. A woman who becomes pregnant in a famine may pass on a warning, inducing her child not to grow to proportions that might be difficult to sustain in hard times.

"Thrifty phenotypes" may not be so well-suited to good times, though. Dutch people born to mothers who were starving under the Nazi occupation have proved to be more vulnerable than most to diabetes, an effect consistent with a metabolism geared to cope with a low sugar intake.

The thrifty phenotype might also explain the relatively low vulnerability enjoyed by the French, despite their hearty diet. In France, the state organised dietary supplements for pregnant women long before other nations. French mothers may therefore have been sending fair weather forecasts to their children for generations, producing a nation geared to process diets of affluence. If so, the rest of Europe should catch up in time, without recourse to red wine.

Although a developmental perspective can take the pathology out of size, it restores it to homosexuality. Since the phenomenon is so common, any "gene for" homosexuality would have to provide some kind of evolutionary benefit, through also being a gene for something else. By contrast, Bateson and Martin suggest various developmental accidents that may underlie the homosexual phenotype, such as the effects on the maternal immune system of earlier male-bearing pregnancies.

There will probably be something in their account to give everybody pause for thought. Yet Bateson and Martin have delivered what others have claimed to provide: a solid, signposted road out of the trench war between nature and nurture.

The writer's book, `As We Know It: Coming to Terms with an Evolved Mind', is published by Granta