Genes and Behavior
Understanding the role of our genetic inheritance requires that we know how genes express themselves. One popular conception is of genes as templates stamping out each human trait whole cloth. In fact, genes operate by instructing the developing organism to produce sequences of biochemical compounds.
In some cases, a single, dominant gene does largely determine a given trait. Eye color and Huntington’s disease are classic examples of such Mendelian traits (named after the Austrian monk, Gregor Mendel, who studied peas). But the problem for behavioral genetics is that complex human attitudes and behavior–and even most diseases–are not determined by single genes.
Moreover, even at the cellular level, environment affects the activity of genes. Much active genetic material does not code for any kind of trait. Instead it regulates the speed and direction of the expression of other genes; it modulates the unfolding of the genome. Such regulatory DNA reacts to conditions inside and outside the womb, stimulating different rates of biochemical activity and cellular growth. Rather than forming a rigid template for each of us, most genes form part of a lifelong give-and-take process with the environment.
The inextricable interplay between genes and environment is evident in disorders like alcoholism, anorexia, or overeating that are characterized by abnormal behaviors. Scientists spiritedly debate whether such syndromes arc more or less biologically driven. If they are mainly biological–rather than psychological, social, and cultural — then there may be a genetic basis for them. Therefore, there was considerable interest in the announcement of the discovery of an “alcoholism gene” in 1990. Kenneth Blum, Ph.D., of the University of Texas, and Ernest Noble, M.D., of the University of California, Los Angeles, found an allele of the dopamine receptor gene in 70 percent of a group of alcoholics — these were cadavers — but in only 20 percent of a non-alcoholic group. (An allele is one form of gene.)
The Blum- Noble discovery was broadcast around the country after being published in the Journal of the American Medical Association and touted by the AMA on its satellite news service. But, in a 1993 lAMA article, Joel Gelernter, M.D., of Yale and his colleagues surveyed all the studies that examined this allele and alcoholism. Discounting Blum and Noble’s research, the combined results were that 18 percent of non-alcoholics, 18 percent of problem drinkers, and 18 percent of severe alcoholics all had the allele. There was simply no link between this gene and alcoholism!
Blum and Noble have developed a test for the alcoholism gene. But, since their own data indicate that the majority of people who have the target allele are not alcoholics, it would be foolhardy to tell those who test positive that they have an “alcoholism gene.”
The dubious state of Blum and Noble’s work does not disprove that a gene — or set of genes — could trigger alcoholism. But scientists already know that people do not inherit loss-of-control drinking whole cloth. Consider this: Alcoholics do not drink uncontrollably when they are unaware that they are drinking alcohol — if it is disguised in a flavored drink, for example.
A more plausible model is that genes may affect how people experience alcohol. Perhaps drinking is more rewarding for alcoholics. Perhaps some people’s neurotransmitters are more activated by alcohol. But although genes can influence reactions to alcohol, they cannot explain why some people continue drinking to the point of destroying their lives. Most people find orgasms rewarding, but hardly any engage in sex uncontrollably. Rather, they balance their sexual urges against other forces in their lives.
Jerome Kagan, Ph.D., a Harvard developmental psychologist, was speaking about more than genes when he noted, “we also inherit the human capacity for restraint.”
Last reviewed: By John M. Grohol, Psy.D. on 27 Aug 2007
