Are Your Genes To Blame?


For your good looks? Sure. For your shyness or your temper? Not entirely

Time, January 20, 2003

Readers of the science pages could be forgiven for thinking that the conversation in the comic strip really took place. Study after study has shown that genes can affect behavior and mental life. Identical twins separated at birth (who share their genes but not their environment) are similar in their intellectual talents, their personality traits (such as introversion, conscientiousness, and antagonism), their average level of lifelong happiness, and personal quirks such as giggling incessantly or flushing the toilet both before and after using it. identical twins (who share all their genes) are more similar than fraternal twins (who share half their genes). And biological siblings (who share half their genes) are more similar than adopted siblings (who share none of their genes). It’s not only personality and intelligence that are partly heritable, but susceptibility to psychological maladies such as schizophrenia, obsessive-compulsive disorder, and major depression.

The discovery that genes have something to do with behavior came as a shock in an era in which people thought that the mind of a newborn was a blank slate and that anyone could do anything if only they strove hard enough. And it continues to set off alarm bells. Many people worry about a Brave New World in which parents or governments will try to re-engineer human nature. Others see genes as a threat to free will and personal responsibility, citing headlines such as “Man’s genes made him kill, his lawyers claim.” Behavioral geneticists are sometimes picketed, censored, or compared to Nazis.
With increasing knowledge of how the genome works, many beliefs about ourselves will indeed have to be rethought. But the worst fears of the genophobes are misplaced. It is easy to exaggerate the significance of behavioral genetics for our lives.

For one thing, genes cannot pull the strings of behavior directly. Behavior is caused by the activity of the brain, and the most the genes can do is affect its wiring, its size and shape, and its sensitivity to hormones and other molecules. Among the brain circuits laid down by the genes are ones that reflect on memories, current circumstance, and the anticipated consequences of various courses of action and that select behavior accordingly, in an intricate and not entirely predictable way. These circuits are what we call “free will,” and providing them with information about the likely consequences of behavioral options is what we call “holding people responsible.” All normal people have this circuitry, and that is why the existence of genes with effects on behavior should not be allowed to erode responsibility in the legal system or in everyday life.

Also, don’t count on the I’ll-let-you-go-now gene –or any other single gene with a large behavioral effect -- being identified any time soon. Behavioral genetics has uncovered a paradox. Studies that measure similarities among twins and adoptees reliably show strong effects of sharing many genes (such as half a genome, or all of one). The outcome is so reliable that behavioral geneticists now speak of the First Law of their field: that all behavioral traits are partly heritable.

But studies that try to isolate a single gene for a behavioral trait have been fickle; many of putative genes-for-X have not held up in replications. Genes must exert their effects by acting together in complex combinations. A rough analogy: a computer program can have a trait, such as being easy to use, without necessarily having a single magical programming instruction that makes any program easy to use when added and any program hard to use when omitted.
So psychological engineering is more remote than the futurologists would have you believe. Though musical talent may be partly heritable, there is probably no single gene for musical talent that ambitious parents can have implanted into their unborn children. It might take hundreds or thousands of the right genes, with a different combination needed for each child.

Finally, the fact that genes matter doesn’t mean that other things don’t matter. Some of these causes are obvious. There are no genes for speaking English or for being a Presbyterian (though there may be sets of genes for verbal skill and religiosity). These depend entirely on one’s culture. Others are less obvious, such as germs, accidents, chance encounters in life, and random events in the development of the brain in utero.

And still other environmental factors may not be act as we think they do. It’s easy to assume that the variation in behavior that is not caused by genes must be caused by parents. But it’s been surprisingly hard to demonstrate any long-term effects of growing up in a particular family within a culture. Identical twins reared together are similar, but they are not literally identical: one may be more anxious than the other, one may be gay and the other straight. This shows that genes are not everything – but since these twins grow up in the same family, it also shows that what isn’t explained by genes isn’t explained by family influences either. Similarly, children need to hear English to acquire it. But if their parents are immigrants, they end up with the accent of their peers, not their parents.

Though the effects of genes may be easy to overestimate, they are also easy to underestimate. Many failed utopias of the twentieth century dreamed of nurturing a “new man” free of selfishness, family ties, and individual differences. Some psychotherapists promise what they cannot deliver, such as transforming a shy person into a bold one or a sad sack into a barrel of monkeys.

None of this means that social and personal improvement are a waste of time. Even if each of us is born with a range of temperament and talent, we can try to reach the best point in that range. And even if we have a nature, part of that nature is an open-ended ingenuity that can think up possible solutions to our problems. Using our genes as an excuse for fatalism is unwise. But so is pretending that they don’t matter at all.

Pinker's latest book is The Blank Slate: The Modern Denial of Human Nature