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Psychology 2550A/B
James M Olson

Heredity andpersonality September-30-12 7:39 PM - Behaviourgenetics studies the role of genes in social behaviour and personality GENETIC BASES OFPERSONALITY - The human genome: the genetic heritage - Genetic heritage of humans is contained in DNA, arranged in 23 pairs of chromosomes ○ DNA - long string of small units called nucleotides, 4 types of nucleotides: A, T, G, C  Each DNA contains about 1.5 gigabytes of genetic information - The analogy that DNA is a blueprint is far from accurate - Agene is a region of DNA that influences a particular characteristic in an organism, and is a unit of heredity ○ They contain a stretch(es) of DNA that specify the structure of a protein to be made ○ Anda stretch called the regulatory sequences, which control whether or not, and how much of, the protein is made ○ Sometimes different proteins can be made based on the same gene - Althoughany unrelated people share about 99.9% of their DNA sequence, people's DNA are not identical (unless identical twins ) ○ Asmall minority of genes are different for different persons and these make each individual genetically distinctive - they are the ones that influence thediverse variations among people in such characteristics as eye colour and height - It would not be surprising if the relatively minute variations in the DNA sequences among people can lead to some significant differences in their physical andbehavioural characteristics - What a cell becomes is determined by biological switches outside the cell that turn the specific genes in the cell on or off - The goal is to understand just how the genes are turned on and off by the physical and social-psychological environment and expressed, and the specific ways in which this process influences how we think, feel, and behave - Studies that compare the similarity in personality shown by individuals who vary in the degree towhich they share the same g enes and/or the same environments - Genes play a huge role in personality TWIN STUDIES - The twin method - Heredity studies use the twin method to assess genetic influence - This method compares the degree of similarity on measures of personality obtained for genetically identical twins (those who are from the same egg/monozygotic, MZ) as opposed to twins who are fraternal (those from a diff fertilized egg, or dizygotic, DZ) - Identical twins must be more similar than fraternal twins - Resultsof twin studies - The resemblance within identical twin pairs tends to be strongest for general ability - it is somewhat lower for personality inventory scales and lowest for interests, goals, and self-concepts - Forpersonality, twin correlations are about .50 for identical twins and .25 for fraternal twins - The big five - Extraversion and neuroticism have been studied the most ○ Extraversion - sociability, impulsiveness, and liveliness ○ Neuroticism - moodiness, anxiousness, and irritability - Temperaments - Temperaments refers to traits that are visible in early childhood and seem relevant to the individual's emotional life - Assessedthrough parental reports about their children on temperament ○ Inadults, they are typically assessed by self-report measures - Emotionality (aka emotional reactivity) is often defined as the tendency to become aroused easily physiologically (by ready activation of the ANS) and especially to experience frequent and intense negative emotions such as anger, fear, distress ○ Someresearchers disagree though and find that the intensity with which an individual experiences emotions is independent of how often he or she has suchfeelings - Positiveand negative emotions can function independently and they need to be measured separately - Sociability refers to the degree to which the person seeks to interact with others and to be with people - Activity may be defined with regard both to the vigor or intensity of responses and their tempo or speed ○ It refers to stable individual differences on a dimension that ranges from hyperactivity toextreme inactivity - Onthe dimension of emotionality, identical twins are rated as much more similar by their mothers than are fraternal twins ○ But this may be faulty bc the mothers may have been influenced by their own expectations ○ Stilltho - these results are so consistent that there must be a genetic significance - Conclusion: 1/3 - 1/2 of individual differences in temperamental traits can be attributed to genetic variation among children - Characteristics with genetic influence ○ Degree towhich the child's behaviour is inhibited ○ Shyness ○ Activity level ○ Empathy - INFOCUS 5.2 inhibited children: kagan's shyness research - Anotable example of research on temperaments that goes much beyond self-reports comes from jerome kagan's long-term research on inhibition and shyness - Kagan argues that inhibition is one of the major dimensions of temperament, and finds early individual differences exist on t his dimension and endure in the course of development - The highly reactive children showed greater fearful behaviour, heart acceleration, and higher blood pressure when they were p ut in an unfamiliar situation - Inshort, temperamental differences in inhibition emerged as early as 4 months, were stable across the first 4 years of life, and showed moderate heritability, suggesting a biological-genetic component in its development - Can stillchange tho - inhibited infants grew up to be less inhibited preschoolers if they had mothers who were not overly protective and placed rea sonable demands on them - Attitudes and beliefs - Asubstantial genetic influence was found on traditionalism- a general orientation that taps conservative (as opposed to liberal) attitudes on diverse topics - Astudy found that the more heritable attitudes were harder toinfluence and also more important in determining the person's judgements of interpersonal attraction - Aggressiveand altruistictendencies - Questions such as: "i try not to give people a hard time" "some people thinki have a violent temper" - Withinidentical (MZ) twin pairs, the answers were more similar than would be expected by chance whereas between fraternal tw ins, the correlation was merely at a chance level - for both males and females - Romantic loveand marriage - One area that seems to be beyond DNA is romantic love - Sixdifferent love styles were measured, ranging from one that values passion, excitement, intimacy, self-disclosure, and "being in love from the start," to one that values a relationship that is affectionate and reliable and has companionship and friendship (like "it's hard for me tosay when our friendship turned into love) - Foundthat how people love is almost completely due to the environment and essentially unaffected by genetic influences - family environment is important - But the propensity to get marries is heritable/genetically influenced - Twins reared apart - There were instances of dramatic psychological similarities within the twin pairs, even for twins who grew up in radically di fferent environments for 30 years ormore in many cases ○ They seemed to share some quite distinctive mannerisms, postures, attitudes, and interests - Many also quickly felt a close emotional connection with eachother even though they had spent their entire lives apart - Test results: similarity was almost as high for the MZ twins who grew up in different homes as it was for those raised within the same family - They attributed 70 percent of the individual differences found in intelligence to heredity - Beyondself-report measures - At least some of the similarity may lie in the eyes of the beholder - for ex, identical twins who have a higher level of frustration tolerance may think and honestly say that they experiences less negative emotions than others, worry less, and rarely feel anxious only because they are less bothered by these feelings - It's therefore particularly important to use measures of personality other than self report questionnaires toinvestigate whether or not this result is somehow due tobiases in the self report measures themselves - Ratings by the peers correlated .55 with the twins' self-report ratings, providing moderate validity for those ratings - Genes accounted for 25 percent of these if...then... Personality signatures ○ Thus, identical twins are more similar in these signatures and in their stable person X situation interactions compared to fraternal twins - INFOCUS 5.3 UNDERSTANDING HERITABILITY AND THE HERITABILITY INDEX - Heritability index - an estimate of the role of heritability in accounting for individual differences on the variable studied ○ Must be interpreted for several reasons:  Heritability estimates always are limited to the specific population that was studied in the research reported  Even when identical twins are reared apart, their similarities on personality measures are not necessarily due to their genes for personality itself  Many studies tat compare the similarity of identical and fraternal twins who grow up together draw mostly on their answers on self-report personality questionnaires  Highheritability coefficients do not imply that the particular characteristic cannot be changed significantly  The heritability index itself does njot address the mecanisms through which the genetic influences on personality operate and exert their effects onthe individual - Heredityversus environment: another false dichotomy - Inshort, regardless of the exact percent used to estimate the influence of genetic factors, clearly their influence is consi derable, especially given that few findings in personality account for as much as 20% of the variance - The same data show that at least half of the variance of personality is not due to genetic factors and thus also attest to th e importance of the environment forpersonality - Recurrent theme: unquestionably one's genetic endowment has extensive influences on one's life and personality development, and so also does the environment - Summary - The findings support the view that genetic factors play a significant role in personality, both in broad traits as measured b y the big five, and in if...then... Behavioural signatures (person X situation interactions), in attitudes and values, as well as in self-esteem - The true heritability estimate for self-reported personality is closer to the adoption study estimate of 20 percent than to the twin study estimate of 40 percent GENE-ENVIRONMENT INTERACTION - Bothnature (genetics) and nurture (environment) are important influences on personality - The unique (nonshared) psychological environment of each family member - Genetic researchers contend that family members resemble each other in personality largely because of genetic influences, and that the environment seems tomake members of a family different - Reasoning is based on two findings: ○ Twins reared apart are only somewhat less similarin personality than twins who grew up in the same family ○ Instudies of adoptive families that have
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