Universal temperament and personality traits are evidence of common evolved history.

The presence of differences in children’s temperament at birth has been taken as evidence of the heritability of personality. Some infants are “easy” and sleep through the night, take nutrition readily, and are a pleasure to be around. Other babies are “difficult” often cry and fuss and wake repeatedly for attention throughout the night. Most parents will have observed some of these differences in their children or those of friends and family. Temperament has been defined as the dominant behavioral mode that is more or less consistent across situations (Strelau, 1998). The study of temperament has long been of interest in behavior genetics and is defined as consistent and dominant behavioral reactions across many social situations (Van der Werff, 1985). For example, we may say a person has an irritable temperament thereby describing a person’s constant negative reaction to a variety of stimuli. The genetic basis for these consistencies in temperament is supported in recent research (Strelau, 1998). However there are problems associated with heritability estimates of temperament and other human characteristics. For example, research has not located a single gene pathway link to specific personality traits. Recently more complex approaches have examined the covariance of several genes linked to behavior (Riemann & De Raad, 1998). Temperament may be the genetic component affecting the infant that explains the development of subsequent personality. Generally the environment is not seen as a significant contributor to personality differences as these individual consistencies are maintained despite varying contexts and conditions.

In recent decades research has found solid support for the presence of universal traits of personality based on five distinct dimensions named openness, conscientiousness, extraversion, agreeableness, and neuroticism. This universal conceptual model was based on many studies that demonstrated similarities in personality dimensions within cultures, but also cross-culturally. The original research discovered five dimensions from factor analyses of trait adjectives that were used to describe the self and others (Juni, 1996). Research has established heritability estimates of personality in a fashion similar to intelligence estimates determining the proportion of the total variance of that can be attributed to genetic inheritance. Heritability estimates have been calculated for the so-called Big Five, including heritability estimates of about .50 for the extraversion-introversion dimension (Bouchard, McGue, Hur, & Horn, 1998). Other cross-cultural research found similar constellation of traits in various societies employing other personality tests as well as trait adjectives (McCrae, Costa, Del Pilar, & Rolland, 1998; Schmitt, Allik, McCrea & Benet-Martinez, 2007).

The proportion of the total behavioral variation attributed to genetic inheritance was determined by comparing correlations between closely related persons like twins to those less closely related genetically. For example the heritability estimates for extraversion are .51 for identical twins, but only .16 for siblings, and .01 for adopted children. Heritability estimates for extraversion based on twin studies is generally around .50, whereas for the other of the Big Five traits the estimates range from .30 to .50 (Bouchard, McGue, Hur, & Horn, 1998). The low heritability estimates for adopted children suggest that the environment has very small affects on extraversion and that the consistency of personality probably is genetically determined or mediated (Plomin, DeFries, McClearn, & Rutter, 1997).

An impressive body of research has continued to support the presence of the Big Five in all societies studied (Hofstede, Kiers, De Raad, & Goldberg, 1997; McCrae, 2001). The measures of the Big Five were administered in 51 cultures and subsequently subjected to factor analysis. Again the data analysis grouped the personality descriptions into the five major factors (McCrae, Terracciano, Leibovich, Schmidt, Shakespeare-Finch, & Naubauer, 2005). In particular strong support was found for the presence of extraversion and neuroticism utilized in a graphic display of a variety of cultures being high or low on these dimensions. In another study Allik and McCrae (2004) found that the relationship in personality between cultures was a function of geographic closeness with participants more closely related in personality sharing both deep geneographic journeys as well as culture. The overall research suggests the presence of the Big Five as a universal model of personality structure.

Again we must be reminded that the research is far from conclusive since no personality trait is caused by a single gene, and it is not possible to dismiss personality-environmental interactions. Research is increasingly recognizing this complexity including the investigation of multiple genes and their interactions (Plomin & Caspi, 1998). This research is just in its infancy, but the results support an important genetic factor in behavior, and the universal basis for personality communalities independent of culture. The issue will be discussed further in chapter 8 on personality.

The universality of both human characteristics and neurophysiologic mechanisms suggest a response to evolutionary mechanisms. The ubiquitous nature of the personality structure and optimism suggest that they have served evolutionary functions in adaptation and in problem solving, and that one might expect corresponding neurophysiologic brain structures (MacDonald, 1998). For example conscientiousness might be functionally advantageous by helping monitor situations that produce punishments. Conscientiousness might also help create the longer view in humans that is functional when individuals must strive for future goals even when tasks are not intrinsically rewarding. For example students need conscientiousness in order to complete uninteresting requirements for a university degree. Consistent behaviors reflected in personality have evolved to motivate people to perform behaviors that ensure reproductive success and motivate functional outcomes.

The Big Five personality traits have been found in all cultures investigated (McCrea et al, 2005) in studies employing a variety of measurement procedures. Again these traits tend to be stable across the lifespan suggesting little environmental influence (McCrae & Costa, 2003). Further research has shown that the relationship between parent and child has largely temporary affects (Rowe, 1994). The research on identical twins also point to a biological basis as the personalities of twins that are reared in independent environments are more similar than those of fraternal twins reared together (Bouchard & Loehlin, 2001). The persistence of personality traits have also been demonstrated over the long run in longitudinal studies pointing to hard wiring in the brain (Borkenau & Ostendorf, 1998).

Date: 2015-01-11; view: 922