0.10 Biology and personality  (Page 5/22)

An even temperament leads to stable behavioral and emotional reactions.

…it is wise to state explicitly that many differences among children may have little to do with temperament…Our current knowledge indicates that the motivation to perform well in school, the willingness to help a friend, loyalty to family, tolerance toward others, and a host of other motives and beliefs are minimally influenced by temperament. (pg. 77; Kagan, 1994)

Recently, Thomas Bouchard, Jr. (2004) offered a concise review of the heritability of psychological traits. With regard to the “Big Five” personality traits, they all exhibit heritability in the range of 42 to 57 percent. If one considers the alternative known as the “Big Three,” the range is 44 to 52 percent (Bouchard, 2004). Thus, genetics make a significant contribution to the nature of basic personality, but at the same time there is at least as much of an environmental contribution (though that certainly includes a variety of factors). There is also significant heritability of psychological interests (such as being realistic, artistic, social, etc.), social attitudes, and psychiatric illness (especially schizophrenia; Bouchard, 2004; see also Bouchard, 1994; Bouchard&McGue, 1990; Bouchard et al., 1990; Kety, 1975; Mendlewicz, Fleiss,&Fieve, 1975; Shields, Heston,&Gottesman, 1975). Even such complex personality variables as well-being, traditionalism, religiosity, and criminality have been found to be highly influenced by our genetic make-up (Crowe, 1975; Kagan, 1994; Kessler, 1975; Tellegen et al., 1988; Waller et al., 1990). To put it simply, virtually all psychological factors are significantly influenced by our genetic makeup, but none are specifically determined by genetics. This led Danielle Dick and Richard Rose (2002) to question whether the field of behavior genetics has completed what it can reasonably hope to accomplish. They argue that there is much more to be studied, particularly in the area of gene-environment interactions . In such interactions, individuals experience the same environment in different ways due to their genetic predispositions.

In Galen’s Prophecy , Kagan (1994) describes the role that he believes the amygdala plays in mediating responses to anxiety-producing stimuli. Eight percent of children demonstrate highly reactive responses to such stimuli, which animal research has shown is associated with increased activity in the amygdala and, consequently, a behavioral inhibition system . As a result, these children either freeze or withdraw from unfamiliar people and situations. In other words, they seem shy and withdrawn. Approximately 18 percent of children demonstrate low reactivity, their amygdala and the behavioral inhibition system are not activated, and they are likely to approach unfamiliar people and situations with curiosity. These simple patterns of behavior can have profound effects on personality. Kagan (1994) has found that high reactive infants , those who become anxious as a result of unfamiliarity, tend to become dour, serious, and fearful as they grow. In contrast, the low reactive infants , those who may respond to unfamiliarity with curiosity and interest, become more joyful and fearless as they grow up. However, these tendencies are by no means guarantees, because the environment plays a significant role. If mothers are firm and set strict limits on the child’s behavior, if they are supportive but do not always hold the child when it is upset (i.e., they hold the child when it needs help, but not when the child does not need help), then a high reactive child has a much better chance of overcoming its tendency to become an anxious and withdrawn person. One explanation, according to Kagan, is that these mothers require their children to meet her socialization demands; they must learn to deal with the uncertainty of unfamiliar situations. As for overprotective parents: