Download
1 / 46
460 likes | 583 Views
Chapter 10 The Biological Approach: Relevant Research. The Heritability of Personality Traits. The nature versus nurture distinction presents a false dichotomy. Both genetic factors and experiential factors influence personality.
E N D
The nature versus nurture distinction presents a false dichotomy • Both genetic factors and experiential factors influence personality. • For this reason, the appropriate questions to ask with regard to the role of biological influences on personality are: • What aspects of personality are influenced by genetic factors? • To what extent are different aspects of personality influenced by genetic factors? • To what extent are genetic influences on personality moderated by one’s “nurture” (one’s life experience, learning history, etc.)? • If predispositions toward physical illness are heritable, are predispositions toward mental illness heritable as well? • If stable abilities and aptitudes such as intelligence are heritable, are personality traits such as the Big Five heritable as well?
Example of a genetically caused disease: Huntington’s disease
Genetic transmission of a disease by unaffected “carrier” parents
Understanding gene testing: What does a predictive gene test tell you? • An accurate gene test will tell you if you do or do not have a disease-related gene mutation. If you do, a variety of factors can influence the chances that you will actually develop disease. Nearly everyone with the familial adenomatous polyposis genes will─unless he or she takes effective preventive measures─someday develop colon cancer. On the other hand, women who carry the BRCA1 breast cancer susceptibility gene have an 80-percent chance of developing breast cancer by the age of 65; their risk is high but not absolute. • Of course, even family members who escape the inherited susceptibility gene are not exempt from risk. Like anyone else, they could develop mutations in that same gene during their lifetimes. Or, they could have inherited a different, unknown susceptibility gene.
Female monozygotic (MZ) twins, also known as identical twins
Who are these famous American twins? Are they identical (MZ) or fraternal (DZ)?
Concordance rates between MZ and DZ twins for various psychological disorders
Identical scores for wonder twins December 18, 2005 Power of two ... Mariel and Annick Lombard received identical UAI scores of 99.9 IDENTICAL twins Mariel and Annick Lombard studied together and tested each other with past exam questions in the lead-up to the HSC. But it took them by surprise when they found out they had received the same UAI of 99.9 yesterday. The Hornsby Girls High School students, 17, both studied three language subjects in the HSC, both coming in the top four in the state in each course. Mariel would like to study arts languages at Sydney University, while Annick wants to do a bachelor of international studies at Macquarie University. Source: The Sun-Herald Photo: Lee Besford
Estimated heritability of various traits and cognitive abilities
Reunited twins These identical twins, separated at birth, were reunited at age 31. Although raised apart, they found that they had a great deal in common. Both had become firefighters, wore mustaches, were balding, had poor vision, enjoyed hunting and fishing, and drank the same brand of beer. T.K.Wanstall/The Image Works
Correlations for identical twins raised apart versus together (Rowe, 1987)
Twin correlations for MZ twins reared together and apart (Tellegen, Lykken, & Bouchard, 1988)
Problems with genetics research on personality • Many “identical” twins may in fact be DZ twins who look very much alike (this is less of a problem now than in the past.) • There is evidence that MZ twins have more similar environments than DZ twins do (violating the major assumption of twin-study research). • Because adoptions are not random events, the environments provided by adopting families might be relatively similar and homogeneous. • Genetics may influence only some personality traits, and then only during certain stages of life, with some gender-specific effects as well. • Because virtually all traits appear to be “polygenic,” some traits may show a particularly high concordance in MZ twins compared to DZ twins because of the more complex influences known as nonadditive effects.
The lemon juice demonstration • It has been reported that introverts produce more saliva than do extraverts (Corcoran, 1964, in Phares, 1991). The lemon juice demonstration provides a test of this effect. • Tie a thread to the center of a double-tipped cotton swab so that it hangs perfectly horizontal. The person swallows three times, then puts one end of the swab on the tongue, holding it there for 30 seconds. • Then four drops of lemon juice are placed on the tongue. After swallowing, the person places the other end of the swab on the same portion of tongue for 30 seconds. • The swab will remain horizontal for extraverts, hang down on the lemon juice end for introverts (indicating a relatively large amount of saliva produced in response to the lemon juice).
Extraversion and preferred arousal level • When students sitting in different types of study areas completed the Eysenck Personality Inventory, the researcher found that extraverts tended to sit in noisier and more public areas whereas introverts tended to sit in quieter and more private areas. • In a study by Geen (1983), extraverts more quickly changed the slides on an audiovisual learning task, suggesting that they were more easily bored than the introverts were. • In Geen’s (1984) study, extraverts and introverts worked on a word-memory task while listening to white noise through headphones. The two groups selected different levels of noise as being optimal and did worse on the task when forced to listen to the noise at a level that was optimal for the average member of the other group.
Extraversion and preferred arousal level • When students sitting in different types of study areas completed the Eysenck Personality Inventory, the researcher found that extraverts tended to sit in noisier and more public areas whereas introverts tended to sit in quieter and more private areas. • In a study by Geen (1983), extraverts more quickly changed the slides on an audiovisual learning task, suggesting that they were more easily bored than the introverts were. • In Geen’s (1984) study, extraverts and introverts worked on a word-memory task while listening to white noise through headphones. The two groups selected different levels of noise as being optimal and did worse on the task when forced to listen to the noise at a level that was optimal for the average member of the other group.
Happiness ratings of extraverts and introverts (Larsen & Kasimatis, 1990)
Why do extraverts report being happier than introverts? • Extraverts tend to socialize more than introverts and therefore experience the benefits of doing that. These benefits include: • Participating in enjoyable, interesting, and exciting activities • Having basic needs met (eating, drinking, sex, feeling loved, feeling accepted, feeling competent) • Having a social support system to applaud one’s successes and help one deal with obstacles, frustrations, and failures • Extraverts may be more sensitive to rewards than introverts (example: getting a good grade on a test of “Syncretic Skill”). • Impulsivity appears to be the price that extraverts pay for their greater reward sensitivity. This impulsivity can create problems for them.
From an evolutionary perspective, what does one gender look for in the other? • What men look for in women: high reproductive value (fertility) and “good genes” • Good facial and body symmetry (one indicator of “good genes”) • Relatively young in age (in the age range of optimal fertility) • Physical attractiveness (e.g. smooth skin, good muscle tone, lustrous hair, full lips) • What women look for in men: “good genes” and the willingness to commit and invest • Good facial and body symmetry (one indicator of “good genes”) • Somewhat older in age (indicates “good genes” and survival potential) • Tall and physically dominant (signals ability to provide protection and resources) • Possesses essential resources (signals potential as a good provider) • Willingness to commit resources to the woman and her children • Personal ads provide one area for intrasexual selection―the competition among members of the same gender for the best members of the opposite sex.
From an evolutionary perspective, what does one gender look for in the other? • What men look for in women: high reproductive value (fertility) and “good genes” • Good facial and body symmetry (one indicator of “good genes”) • Relatively young in age (in the age range of optimal fertility) • Physical attractiveness (e.g. smooth skin, good muscle tone, lustrous hair, full lips) • What women look for in men: “good genes” and the willingness to commit and invest • Good facial and body symmetry (one indicator of “good genes”) • Somewhat older in age (indicates “good genes” and survival potential) • Tall and physically dominant (signals ability to provide protection and resources) • Possesses essential resources (signals potential as a good provider) • Willingness to commit resources to the woman and her children • Personal ads provide one area for intrasexual selection―the competition among members of the same gender for the best members of the opposite sex.
Mean age difference between preferred age for spouse and self in international data
From an evolutionary perspective, what does one gender look for in the other? • What men look for in women: high reproductive value (fertility) and “good genes” • Good facial and body symmetry (one indicator of “good genes”) • Relatively young in age (in the age range of optimal fertility) • Physical attractiveness (e.g. smooth skin, good muscle tone, lustrous hair, full lips) • What women look for in men: “good genes” and the willingness to commit and invest • Good facial and body symmetry (one indicator of “good genes”) • Somewhat older in age (indicates “good genes” and survival potential) • Tall and physically dominant (signals ability to provide protection and resources) • Possesses essential resources (signals potential as a good provider) • Willingness to commit resources to the woman and her children • Personal ads provide one area for intrasexual selection―the competition among members of the same gender for the best members of the opposite sex.
Importance of a “good financial prospect” when women select a mate
Some caveats about evolutionary personality psychology • Differences in men’s and women’s preferred age for a marriage partner may have to do with maturity level rather than evolved psychological preferences, because women mature physically―and perhaps emotionally―more quickly than men. • Researchers do not always produce findings consistent with evolutionary psychology’s predictions. • The needs of primitive humans in the wild may differ greatly from those of contemporary humans in modern society. For example, in contemporary society women may prefer a partner who spends time with them to one who devotes all his time to acquiring resources. • The evolutionary approach has little or nothing to say about homosexual mating choices or to people who are past their reproductive years.
