Chapter 21: Biology and Personality

Part 2: Genetically Determined Dispositions

Behavior genetics is the term most commonly used to refer to studies on the influence of genetics on behavior.  Most of these studies have relied on comparing identical twins to fraternal twins, other siblings, and unrelated individuals, including twins who have been reared apart.  These studies are often conducted in European countries that have thorough records of family histories, but one major, longitudinal study ongoing here in the United States has been the Minnesota Twin Family Study conducted at the University of Minnesota since 1983.  These various sources of data, in addition to other research procedures, have helped psychologists come to some understanding of the role played by genetics in determining behavior and personality.

Psychologist Jerome Kagan is well known for his early studies on the nature of temperament.  Temperament is perhaps the most salient characteristic of personality.  It has been loosely described as the emotional component of our personality, as stable behavioral and emotional reactions that appear early in life and are influenced by genetic factors (Kagan, 1994).  Kagan further describes temperamental categories as qualities that (1) vary among individuals, (2) are moderately stable over time and in different situations, (3) are partly determined by genetics, and (4) appear early in life.  In part because they were easy to observe, the most popular temperamental qualities that have been studied are activity, irritability, and fearfulness, or as Kagan describes them: watchful inhibition vs. fearless exploration. About 10 percent of children exhibit extreme inhibition to nonthreatening, but unfamiliar, events (Kagan, 1984).  Although this behavior can seemingly be altered by parental influence, subtle signs of the behavioral inhibition can be seen as the child grows, and they tend to continue into adulthood. Similarly, with uninhibited children, it is extremely unlikely that they will ever become inhibited children. Further studies on twins have helped to confirm that being inhibited or outgoing is influenced by genetics (Kagan, Kearsley, & Zelazo, 1978).  Similar results have also been found with Guatemalan and Chinese children (Kagan, Kearsley, & Zelazo, 1978). As important as our emotional reactions are (see, e.g., the work of Daniel Goleman, 1995, 1998), they still do not necessarily dominate our personality:

…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:

…It appears that mothers who protect their high reactive infants from frustration and anxiety in the hope of effecting a benevolent outcome seem to exacerbate the infant’s uncertainty and produce the opposite effect.  This result is in greater accord with the old-fashioned behavioristic view than with the modern emphasis on the infant’s need for a sensitive parent. (pg. 205; Kagan, 1994)

In support of Kagan’s studies, Fox and his colleagues have demonstrated a specific gene-environment interaction that predicts behavioral inhibition in children aged 14 and 84 months (young 1 year-olds and 7 year-olds; Fox et al., 2005).  Although it is difficult to describe such studies in simple terms, suffice it to say that children with a combination of the short 5-HTT allele (a gene for the molecule that transports the neurotransmitter serotonin) and low social support are at an increased risk for behavioral inhibition.  When the children were 1 year old, behavioral inhibition was measured in terms of the latency to approach novel objects and unfamiliar adults, and when the children were 7 years old it was measured in terms of their disconnection from a group of children at play. The short allele of the 5-HTT gene has been associated with increased anxiety, negative emotionality, and relatively strong coupling with the amygdala.  Therefore, in the absence of social support, children with the short allele are more likely to experience stress in the presence of novelty and strangers (Fox et al., 2005). Moffitt, Caspi, and Rutter have written an excellent review of how psychologists and other scientists approach this important new field of gene-environment interactions, and in that review they suggest that it is most likely that such interactions are common in psychopathology (Moffitt et al., 2006).

Jerome Kagan studied temperament, and found that approximately 10% of children are shy and inhibited and approximately 20 percent of children are curious and adventurous, and these temperaments are most likely to continue into adulthood.  Consider the people you know. Have their basic temperaments remained constant throughout their lives? What about you?

References

Text:  Kelland, M. (2017). Personality Theory. OER Commons. Retrieved October 28, 2019, from https://www.oercommons.org/authoring/22859-personality-theory.  Licensed under CC-BY-4.0.