• DOI:10.1038/3319
• Corpus ID: 44396628

Living With Our Genes

@article{Davies1998LivingWO,
  title={Living With Our Genes},
  author={Kevin Davies},
  journal={Nature Medicine},
  year={1998},
  volume={4},
  pages={1325-1326}
}

• K. Davies
• Published 1 November 1998
• Psychology
• Nature Medicine

In just a few short years, if current estimates are to be believed, the scientific community will be bracing itself for the so-called ‘post-genomic era’. With the complete inventory of human genes downloaded onto their desktops, researchers will have an invaluable resource with which to study all facets of human biology, with one area of particular fascination being human behavior and cognition. This genetic windfall will provide a truly historic opportunity to gauge the roles of nature and nurture in human development. That genes have an important role in shaping human behavior is incontrovertible. A legion of twin studies have underscored varying degrees of heritability for behavioral traits ranging from alcoholism to extroversion (even if you regard anecdotal reports of separated-atbirth identical twins curiously partial to the same brand of toothpaste as mere coincidence). But assigning specific behaviors to individual genes is another matter entirely—as anyone who has witnessed the fluctuating fortunes of the psychiatric genetics field over the past decade can attest. Five years ago, however, two remarkable studies showed that single genes might, in some settings, exert profound effects on human behavior. One report dealt with a Dutch family in which several men had a history of violent anti-social behavior, including arson, attempted rape and incest. Researchers found that these abusive men possessed a nonsense mutation in the X-linked gene for monoamine oxidase type A. This flaw has not been described in any other families, but strongly suggests nonetheless a direct link between serotonin turnover and behavior. The second paper was by Dean Hamer and colleagues who, again focusing on the X chromosome, found clear evidence for a gene associated with homosexual orientation in men. Hamer’s group found that 33 of 40 pairs of gay brothers had inherited the same small region near the tip of the long arm of the X chromosome— significantly more than would have been expected by chance. This high-profile publication and accompanying media hype left Hamer the impossible task of playing down the naïve notion of a solitary ‘gay gene’ while emphasizing how his study reinforced earlier twin studies that had already hinted at an inherited component to sexual orientation. Although few studies since then have matched the impact—and controversy— of these two findings, a growing number of reports describing associations between genes and various behavioral and cognitive traits have made headlines recently. Hamer himself has been closely involved with studies on the genetics of well-known psychological traits such as novelty-seeking and harm-avoidance, and thus is well qualified to describe the latest insights and implications of these fascinating studies in Living with our Genes. The book—Hamer’s second effort in collaboration with science writer Peter Copeland—is written in an extremely accessible manner, with each chapter focusing on a different trait, such as anger, addiction, worry and so on. Each behavior is illustrated by means of case studies and highlights of the latest relevant advances in molecular genetics. Whatever its flaws, it is good to see a prominent scientist such as Hamer taking time out to try to communicate his work and motives to a non-specialized audience. But regrettably, especially given the inherent interest in the subject matter and the author’s noble intentions, Living with our Genes is more style than substance. The first few chapters concentrate on important personality traits such as thrill-seeking, neuroticism and addiction, for which many researchers (including Hamer) have been pursuing a candidate-gene approach, with particular emphasis on proteins involved in the turnover of neurotransmitters such as dopamine and serotonin. This approach turned up trumps in 1996 when an Israeli group reported (and Hamer’s group confirmed) that a length polymorphism in one of the dopamine receptor genes (D4DR) is associated with novelty-seeking. One year later, it was a variant of the serotonin transporter being associated with harm-avoidance. Hamer and Copeland’s breezy account of these discoveries is followed by the equivalent of a government health warning: neither gene alteration accounts for more than about 10 percent of the genetic variance in the respective trait and 5 percent of the total. But there is scant acknowledgement of the fierce divisions in this field, and many important questions remain unanswered: Why are these studies so frequently irreproducible in different populations? How many more genes are likely to be involved in these traits? The authors next discuss the role of serotonin and dopamine in sexual behavior, at which point any semblance of caution is abandoned. “[P]eople with the short serotonin transporter gene have sex more frequently than do people with the long form of the gene” the authors state categorically, which “will come as no surprise to psychiatrists and sexologists”. What about the gene for promiscuity? “Straight men with the long [D4DR] gene,” the authors continue, “...were six times more likely to have slept with another man than those with a short gene.” Evidently size does matter—the size of your genes, that is! These preliminary findings must be corroborated before being passed off as the plain truth. In contrast, Hamer is surprisingly coy when it comes to the work on sexual orientation. Perhaps this is because the subject was covered in his first book (The Science of Desire) or maybe because, so far, no group other than Hamer’s has published any results on the existence of the putative X-linked sexual orientation gene. This very unfortunate dearth of activity is simply attributed to the controversy surrounding the original claims—hardly a satisfactory explanation. In keeping with the implicit target audience, Living with our Genes serves up frequent crude stabs at pop psychology. “Are you a thrill seeker?” the authors tease at the end of the opening chapter. Yes indeed, they conclude, if you’re more intent on perusing babes than books at Barnes & Noble, but apparently not if you’re curled up reading in bed with a steaming cup of cocoa. For those at the 1998 Nature America Inc. • http://medicine.nature.com