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What’s Not in Your Genes

1.

If, by magic, I could make a single interminable debate disappear, I’d probably pick “nature versus nurture.” The argument over the relative roles of genes and environment in human nature has been ceaselessly politicized, shows little sign of resolution, and has, in general, grown tiresome. This is perhaps most obvious in the bloodiest battle of the nature–nurture war, the debate over IQ: How much of the variation that we see in intelligence (at least as measured by standardized tests) is due to heredity and not upbringing? From Francis Galton’s Hereditary Genius (1869) through Stephen Jay Gould’s The Mismeasure of Man (1981) to Richard Herrnstein and Charles Murray’s The Bell Curve (1994), the battle has raged one way and the other, with no clear victor emerging.

It’s good to learn, I suppose, that I’m not the only one who finds the argument annoyingly long-lived. The dust jacket of Matt Ridley’s new book, Nature via Nurture, features statements from a number of scientists and science writers admitting that they had thought it impossible to produce an interesting new book on the subject. In such a climate, if you’re going to attempt yet another work on nature– nurture, you’d better have something truly new, something really big, to say. Matt Ridley does.

Ridley, a science journalist whose previous books include The Red Queen (1993) and the best-selling Genome (1999), has produced a volume that ranges over a vast number of topics, from the genetics of mental illness to the mystery of free will. But at its core are Ridley’s ideas on how to break free of the conflict between nature and nurture. His way out is vaguely Wittgensteinian. We have, he suggests, been asking a meaningless question, making a meaningless distinction. For the question of nature versus nurture makes sense only if the two can be clearly separated. Ridley thinks they cannot. His reason is simple. Despite all the talk about the opposition between genes and environment, it is now clear that learning, intelligence, behavior, and culture—all the ingredients of nurture—involve genes.

At first it might seem that Ridley is making the banal claim that there’s no learning without brains and no brains without genes. All culture is therefore genetic but in the trivial sense that gray matter requires genetic matter. Though Ridley does slip into such platitudes now and then (“you need nature to be able to absorb nurture”), his real point is bigger and more sophisticated. It is this: study of the human genome has revealed that genes respond to experience.

Ridley’s claim depends on several facts from genetics. All of your cells, with rare exceptions, contain the same genes. These genes are made of DNA. It is this DNA, of course, that gets passed from one generation to the next, making children resemble their parents. But DNA’s main job is to make proteins: each of your genes directs the construction of one kind of protein. One of your genes, for instance, makes the protein insulin. You are, roughly speaking, made up of proteins and the products of proteins. If you are dark-skinned, it’s not because your DNA is dark, but because your DNA directed the construction of a protein that looks dark. The fact that some people are albinos means that their DNA is slightly different from your DNA and so directed the construction of a somewhat different protein.

Now you might sense an apparent problem here. If all your cells carry the same genes, why does your pancreas look different from your skin? The reason is that not all of your genes are “expressed”—that is, not all of them are actively making proteins—in all of your cells. Instead, one subset of genes is expressed in your pancreas and another subset is expressed in your skin. The gene that makes insulin, for example, does so only in your pancreas; it is “off” in your skin. This has been understood for a long time. Ridley is excited about a related, but more recent, finding. Some genes, it turns out, are not permanently on or off but can get switched on or off by experience. Genes in your brain cells, for instance, do not just sit there, doing the same thing day in and day out. Instead, some of them can switch on and off in response to what happens outside you. The proteins in your brain thus change somewhat depending on your experiences.

Vision provides a good example of this interplay between experience and genes. In many mammals the development of normal vision requires exposure to light during a critical period following birth. Mice reared in darkness during this period are blind when they become adults. As Ridley explains, there is now good evidence that exposure to light switches on a key gene called BDNF (for brain-derived neurotrophic factor) in the visual cortex of the mouse brain and, presumably, the human brain as well. (Closing a mouse’s eye causes a decrease in the expression of BDNF in the brain.) So development of the brain circuitry needed to see involves experience but, curiously, this experience acts through the genes. As Ridley concludes:

Genes are not puppet masters or blueprints. Nor are they just the carriers of heredity. They are active during life; they switch each other on and off; they respond to the environment. They may direct the construction of the body and brain in the womb, but then they set about dismantling and rebuilding what they have made almost at once—in response to experience.

Ridley’s chief claim is that the “startling new truth that has emerged from the human genome…has profound implications for the nature–nurture debate.” Indeed, it “is about to recast the debate entirely. No longer is it nature versus nurture, but nature via nurture.” The attempt to cleave into two distinct parts the fluid interaction of gene, brain, and experience is fundamentally misguided. We are one big interaction. At times Ridley sounds like a latter-day Augustine wrestling with the mystery of the Incarnation. Human nature does not result from genes alone or from experience alone. Nor is it even partly genetic and partly environmental. Instead human nature is wholly genetic and wholly environmental.

Ridley thinks the consequences of this new view are enormous. By recasting a century of confused talk about nature and nurture, the study of the genome will likely revolutionize our understanding of “what makes us human.” We will be forced “to abandon cherished notions” and biologists may even be obliged to redefine the gene. At one point Ridley even goes so far as to announce that he hopes to throw the whole notion of causation into confusion.

For all his revolutionary rhetoric, Ridley sees himself as a calming influence, a mediator between the historical extremes of nativism and empiricism. And so he is. His approach is refreshingly free of the dogmatism and hubris that often characterize scientific pronouncements on human nature. Although he is, for example, fond of evolutionary psychology—indeed one of his previous books praised sociobiological theories of the origin of morality1—he seems to appreciate that its public champions have sometimes gone too far. Similarly, while he is eager to play up the role of culture he thinks empiricists must overcome their dread of DNA:

Somehow the adherents of the “nurture” side of the argument have scared themselves silly at the power and inevitability of genes and missed the greatest lesson of all: the genes are on their side.

Nature via Nurture has many strengths. For one, the book is packed with fascinating facts about biology. Ridley’s descriptions of how genes act in brains are a tour de force and are astonishingly free of oversimplification. Ridley also manages to tell us a good deal about the lives of scientists. (I, for one, did not know that a sex scandal brought down the behaviorist J.B. Watson’s academic career.) But most important Ridley preaches several sermons that are worth hearing. If, when you think of genes, you think of molecular martinets who bark orders but take none, you have the wrong idea. Genes do turn on and off in response to experience. Ridley also works hard to dispel the myth that environmental effects are reversible while genetic ones are not. In many cases the opposite is true (think of Chinese foot-binding as opposed to genes causing myopia).

Ridley guides us through all of this in prose that is generally both clear and entertaining. Now and then, though, the entertainment takes over and Ridley’s writing slips into silliness. Though his books are usually free of the cloying literary devices that often plague pop science—chief among them the too-cute metaphor that obscures more than clarifies—Nature via Nurture is an exception. Thus we get treated to Ridley’s pet name for the evolutionary force that he thinks shapes the contents of our genes: the Genome Organizing Device, or GOD. While several recent science popularizers have been accused of deifying natural selection, Ridley is, to my knowledge, the first to do so literally. Worse, this GOD barely reappears after His early debut and the reasons for His creation remain unclear.

Ridley’s discussion of weightier matters is also sometimes superficial. At two places in Nature via Nurture, for example, he tries to explain G.E. Moore’s naturalistic fallacy. In his first attempt he notes, “To base any moral position on a natural fact, whether that fact is derived from nature or from nurture, is asking for trouble,” which seems less than helpful. (It would be nice to know why it’s asking for trouble.) In his second try, we learn that an argument is bad because it “would be to commit the naturalistic fallacy…which the GOD forbid.” It’s hard to know what this could mean.

But on the whole Nature via Nurture is an enjoyable book and it would be churlish to make too much of such slips. Ultimately, however, Ridley’s book must be judged on its scientific, not literary, merits. And here matters are more mixed.

2.

The problem is certainly not that Ridley is naive about molecules. His molecular tales are invariably informative and I would, without hesitation, recommend his book as a clear introduction to how genes work. The problem is that the facts Ridley surveys do not always have the larger implications he thinks they do. This problem appears at least twice before Ridley gets to the question of nature and nurture.

First, Ridley argues that not only do genes turn on and off but that this is why species differ. Human beings and chimps, for instance, do not differ because of old-fashioned changes in the genes themselves but, he says, because of changes in when and where the same genes get switched on and off in the two species. But Ridley’s leap from molecular fact to evolutionary implication is premature. Indeed he seems not to realize that he has stepped into a large evolutionary debate between those who suspect species differ in the genes themselves and those who suspect they differ in the “expression pattern” of the same genes. While Ridley’s guess might well turn out to be right, the only fair assessment of our current situation is that we don’t know.

  1. 1

    The Origins of Virtue: Human Instincts and the Evolution of Cooperation (Viking, 1996).

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