ARE human personalities in all their variety—mad, bad, brilliant, extrovert or depressive—essentially the result of nature, of the genes we inherit from our parents? Or are we made by the worlds—social, economic and familial—into which we are born? According to Matt Ridley, this is a question you should not ask. Nature and nurture collaborate; they are partners, not competitors. Every human characteristic depends both on the genetic package we inherit and on the world into which we are born. No gene by itself makes anything. No environment makes a human mind without the collaboration of human genes packaged into a human egg.
So far, so good. But the reality is that despite, or even because of, considerable confusion and ignorance (and goodness knows there has been plenty of both), the nature-versus-nurture debate continues to burn in every field in which human biology bumps up against the study of human social life. It rages over issues ranging from the origin of our most distinctively human capacities—language, trade, technology—to the causes of specific diseases.
The debate has persisted, despite repeated attempts to bury it, because behind the apparent consensus there continue to be important and sometimes politically charged differences. And many of these differences are still hard to adjudicate.
Mr Ridley discusses David Buss's work on cross-cultural universals of male and female sexual preference. In case granny has not already told you, men place more weight on youth and beauty; women more weight on wealth. Some researchers have questioned these results but, on the whole, they hold true across different cultures. At the same time, the difference between men and women is not always huge and there exist considerable differences within the same sex, and even within the same culture. On most criteria, the curves for the two sexes overlap: women care more about their partner's resources, on average, than men. But it is far from true that all men, or all women, bring the same criteria with the same weights to the marketplace of sexual choice. Thus there will also be men who care more about wealth. If this is the case, does the information as a whole show the extensive shaping of sexual choice by natural selection acting differently on men and on women? Or does it show the importance of individual histories of development? A more plausible explanation may be that we still cannot predict with any degree of certainty, for example, just how plastic male sexual taste may be over the full range of human social possibility?
Another issue that interests Mr Ridley, a former science editor of The Economist, is the effect of variation. Would a small difference in the dose of genes you got, or a small difference in your circumstances, make a significant difference to your mind or personality? It depends, of course, on which genes and which circumstances. One continuing theme in “Nature via Nurture” is that although environments matter, within broad limits, differences between environments do not matter much. Small genetic differences quite often have predictable and significant effects. Small environmental differences often do not. So long as the world—in this case the family and its structure—is not too aberrant, most predictable phenotypic differences will be the result of genetic differences, sometimes quite small ones, not environmental differences. Twins reared apart resemble one another in an impressively wide range of personality characteristics, rather than resembling other children from the same rearing environment.
Mr Ridley accepts that this pattern is not universal: he discusses a study on criminal behaviour, which may show that some criminality might be the result of the confluence of genetic and environmental bad luck. But despite such examples, the idea that small genetic differences have more of an effect than small environmental differences comes up again and again. It does so in his discussion of IQ, of the development of personality traits, language and socialisation.
“Nature via Nurture” is a tour through the cutting-edge science on human development and human evolution. It is also a bet that variation in genetic endowment typically matters more than variation in family and social circumstances. Although he claims to want to reconcile the naturists with the nurturists, the author's heart is pretty obviously with nature and he is at least as much a warrior as a peacemaker.
The political implications of Mr Ridley's bet—on education and the law, to cite two examples—may be huge, though its prospects are harder to assess. One of the book's strengths is that the science he examines is so new. That also makes it far from bankable. In some instances an opposing view to Mr Ridley's will have the upper hand: for example, Frank Sulloway's “Born to Rebel” (Vintage, 1997) which shows the effects on personality of birth order within family structure.
“Nature via Nurture” will not bring peace nor will it end the debates about human nature between those who look to biology and those who prefer the social sciences. In his plunge into the fray, however, Matt Ridley offers an excellent view of the battlefield, and characteristically he prefers to ride in the front tank rather than the UN observer's chopper.
This article appeared in the Books & arts section of the print edition under the headline "The generation game"