| | Genetic Underpinnings of Behavior | ...Genes significantly influence animal behavior. The subject becomes very controversial, however, when we come to the behavior of the most complex of animals, Homo sapiens. Behavioral geneticists find evidence of a genetic influence on schizophrenia, alcoholism, sleep disorders, depression, sexual orientation, intelligence quotient, and many personality traits. Consider, for example, sexual orientation, an intensely heated issue in which one side argues that people are born with a hereditary predisposition to become homosexual or heterosexual, and the other side argues that homosexuals simply "choose to be that way" and could change if they wanted to, or that this behavior was caused by childhood influences and can be "corrected" by such means as psychotherapy. J. M. Bailey and R. C. Pillard studied families with two or more male siblings, at least one of whom was homosexual. In 52 percent of the cases where the brothers were monozygotic (genetically identical) twins, the other brother was also homosexual; in 22 percent of dizygotic (nonidentical) twin pairs, the second brother was homosexual; and in only 9 percent of nontwin brothers, the second brother was homosexual. The 52 percent figure shows that genes do not inevitably determine sexual orientation; if they did, this figure would be 100 percent. But the contrast between this datum and the other two does suggest that heredity significantly increases the likelihood of a given adult sexual orientation. ...Genes may influence human behavior, but they do not enslave people. All behaviors require at least some contribution from genes (to build sense organs, nervous systems, muscles, and the other equipment of behavior) and environment (to provide the raw materials to build this equipment and the experiences that sway gene expression). As evolutionary theorist Richard Dawkins puts it, behavior is like a chocolate cake, needing both a recipe and ingredients. Genes provide the behavioral recipe, and the environment the ingredients. Finally, there is no such thing as a gene for any behavior. There is no aggression gene, no gay gene, no gene for bird song or nut-burying. Genes encode proteins, nothing more; but through proteins, they can influence behavior. Aggression and sexual behavior, for example, are influenced by testosterone, and testosterone is synthesized by enzymes, which are proteins encoded by deoxyribonucleic acid (DNA). Thus one can see how genes would influence these behaviors. All behavior, furthermore, depends on chemical signals (neurotransmitters) that are released by one neuron and bind to receptors on the next neuron. Neurotransmitters, too, are synthesized by enzymes encoded by DNA, and their receptors are proteins as well. Neurotransmitter levels control mood and probably aspects of personality. The list goes on and on. Indeed, it is impossible to see how genes could not play a role in behavior. | Kenneth S. Saladin and Ricki Lewis, Genetic Basis of Behavior, Entry in Biology Vol 1 (Macmillan Science Library), Editor-in-chief Richard Robinson | Indexes/07 |
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Finally, we do not have such activities as one of the genes. There is no aggression gene, no gay gene, gene - or bird nut stores. The genes encoding proteins, but nothing more, protein, and they affect the action suit.
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