Hockenbury Discovering Psychology 5th txtbk

The Trait Perspective on Personality445The field of behavioral genetics studies the effects of genes and heredity onbehavior. Most behavioral genetics studies on humans involve measuring similaritiesand differences among members of a large group of people who are geneticallyrelated to different degrees. The basic research strategy is to compare the degree ofdifference among subjects to their degree of genetic relatedness. If a trait is geneticallyinfluenced, then the more closely two people are genetically related, the moreyou would expect them to be similar on that trait (see Chapter 7).Such studies may involve comparisons between identical twins and fraternal twinsor comparisons between twins reared apart and identical twins reared together (seethe In Focus box, “Explaining Those Amazing Identical-Twin Similarities”). Adoptionstudies, in which adopted children are compared to their biological and adoptiverelatives, are also used in behavioral genetics.Evidence gathered from twin studies and adoption studies shows that certainpersonality traits are substantially influenced by genetics (see Caspi & others, 2005).The evidence for genetic influence is particularly strong for extraversion and neuroticism,two of the Big Five personality traits (Plomin & others, 1994, 2001; Weiss& others, 2008). Twin studies have also found that openness to experience, conscientiousness,and agreeableness are also influenced by genetics, although to a lesserextent (Bouchard, 2004; Harris & others, 2007).So is personality completely determined by genetics? Not at all. As behavioralgeneticists Robert Plomin and Essi Colledge (2001) explain, “Individual differencesin complex psychological traits are due at least as much to environmental influencesas they are to genetic influences. Behavioral genetics research provides the best availableevidence for the importance of the environment.” In other words, the influenceof environmental factors on personality traits is at least equal to the influence ofgenetic factors (Rowe, 2003). Some additional evidence that underscores this pointis that identical twins are most alike in early life. As the twins grow up, leave home,and encounter different experiences and environments, their personalities becomemore different (Bouchard, 2004; McCartney & others, 1990).Behavioral genetics has documented,without a shadow of a remainingdoubt, that personality is to somedegree genetically influenced: Identicaltwins reared apart have similar traits.The tabula rasa view of personality asa blank slate at birth that is writtenupon by experience, for many years abasic assumption of theories of allstripes, is wrong.DAVID C. FUNDER (2001)Genes confer dispositions, notdestinies.DANIELLE DICK & RICHARD ROSE (2002)behavioral geneticsAn interdisciplinary field that studies theeffects of genes and heredity on behavior.Evaluating the Trait Perspective on PersonalityAlthough psychologists continue to disagree on how many basic traits exist, they dogenerally agree that people can be described and compared in terms of basic personalitytraits. But like the other personality theories, the trait approach has its weaknesses(Block, 1995).One criticism is that trait theories don’t really explain human personality (Pervin,1994). Instead, they simply label general predispositions to behave in a certain way.Second, trait theorists don’t attempt to explain how or why individual differencesdevelop. After all, saying that trait differences are due partly to geneticsand partly to environmental influences doesn’t say much.A third criticism is that trait approaches generally fail to addressother important personality issues, such as the basic motives that drivehuman personality, the role of unconscious mental processes, how beliefsabout the self influence personality, or how psychological changeand growth occur (McAdams, 1992). Conspicuously absent are thegrand conclusions about the essence of human nature that characterizethe psychoanalytic and humanistic theories. So, although trait theoriesare useful in describing individual differences and predicting behavior,there are limitations to their usefulness.As you’ve seen, each of the major perspectives on personality hascontributed to our understanding of human personality. The fourperspectives are summarized in Table 10.5.Our discussion of personality would not be complete without adescription of how personality is formally evaluated and measured.In the next section, we’ll briefly survey the tests that are used in personalityassessment.Why Are Siblings So Different? Althoughtwo children may grow up in the samehome, they experience the home environmentin very different ways. Even an eventthat affects the entire family, such as divorce,unemployment,or a family move, maybe experienced quitedifferently by eachchild in the family(Dunn & Plomin, 1990).Children are also influencedby varied experiencesoutside thehome, such as their relationshipswith teachers,classmates, andfriends. Illness and accidentsare other nonsharedenvironmentalinfluences. Of course,sibling relationshipsare themselves a potentialsource of influenceon personalitydevelopment.