The internal brand of the scarlet

2. We also think that we have become sophisticated in saying that many genes, not just a Davenportian unity, set the hereditary basis of complex behaviors. But we then take this correct statement and impose the reductionist error of asserting that if behavior A is influenced by ten genes and is 50 percent genetic (by the first error), then each gene must contribute roughly 5 percent to the totality of the behavior. But complex interactions are not built as the sum of independent parts considered separately. I am not one-eighth of each of my great-great grandparents (although my genetic composition may be roughly so determined); I am a unique product of my own interacting circumstances of social setting, heredity, and all the slings and arrows of individual and outrageous natural fortune.

3. We think that we are being sophisticated in qualifying statements about "genes for" traits by admitting their only partial, and often small, contribution to an interactive totality. Thus, we think we may legitimately talk of a "gay gene" so long as we add that only 15 percent of sexual preference records its operation. We need to understand why such statements are truly meaningless and therefore worse than merely false. Many genes interact with several other factors to influence sexual preference, but no separable "gay gene" exists. Even to talk about a "gene for" 10 percent of behavior A is to commit the old Davenportian fallacy on the "little bit pregnant" analogy.

To give a concrete example of how a good and important study can be saddled with all these errors in public reporting (and also by careless statements of some participating researchers), the New York Times greeted 1996 with a headline on the front page of its issue for January 2: "Variant Gene Tied to a Love of New Thrills." The article reported on two studies in the January 1996 issue of Nature Genetics. Two independent groups of researchers, one working with 124 Ashkenazi and Sephardic Jews from Israel, the other with a largely male sample of 315 ethnically diverse Americans, found a clearly significant, if weak, association between propensity for "novelty-seeking behavior" (as ascertained from standard survey questionnaires) and possession of a variant of a gene called the D4 dopamine receptor, located on the eleventh chromosome and acting as one of at least five receptors known to influence the brain's response to dopamine.

This gene exists in several variant forms, defined by differing lengths recording the number (anywhere from two to ten) of repeated copies of a particular DNA subunit within the gene. Individuals with a high number of repeated copies (that is, with a longer gene) tended to manifest a greater tendency for novelty-seeking behavior - perhaps because the longer form of the gene somehow acts to enhance the brain's response to dopamine.

So far, so good - and very interesting. We can scarcely doubt that heredity influences broad and basic aspects of temperament - a bit of folk wisdom that surely falls into the category of "what every parent with more than one child knows." No one should be at all offended or threatened by the obvious fact that we are not born entirely blank or entirely the same in our mixture of the broad behavioral propensities defining what we call "temperament." Certain genes evidently influence particular aspects of brain chemistry, and brain chemistry surely affects our moods and behaviors. We know that basic and powerful neurotransmitters, such as dopamine, strongly impact our moods and feelings (particularly, for dopamine, our sensations of pleasure). Differing forms of genes that affect the brain's response to dopamine may influence our behaviors, and a form that enhances the response may well incline a person toward novelty-seeking activities.