Psychology Dictionary of ArgumentsHome
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| Twin studies: Twin studies in psychology are research methods that compare the similarities and differences between monozygotic (identical) and dizygotic (fraternal) twins to understand the influence of genetics versus environment on human traits, behaviors, and diseases. These studies help to estimate heritability—the proportion of variation in traits attributable to genetic factors—providing insights into nature versus nurture debates. See also Heritablity, Nature versus nurture, Behavior, Personality traits._____________Annotation: The above characterizations of concepts are neither definitions nor exhausting presentations of problems related to them. Instead, they are intended to give a short introduction to the contributions below. – Lexicon of Arguments. | |||
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Thomas J. Bouchard on Twin Studies - Dictionary of Arguments
Corr II 158 Twin Studies/Behaviour/MISTRA/Study/Bouchard/Johnson: Researchers had realized early on that twins who were separated early in infancy and reared in different homes could offer particularly strong tests of genetic influence because, at least in the most direct sense of ‘environmental influence’ (after birth), any similarity in such pairs has to be due to genetic influence. (…) the Minnesota Study of Twins Reared Apart (MISTRA; Segal, 2012)(1) II 157 brought the gravitational centre of discussion ‘around the corner’ from general denial to general acceptance of the idea of genetic influences on behaviour II 158 and psychological characteristics. At 139 pairs, MISTRA was by far the largest study of reared-apart twins. The sample was recruited beginning in 1979 over a period of 20 years, through many different sources ranging from members of the adoption movement and social work and other professionals to individuals who had recently learned they had a twin, heard of the project, and were seeking help in finding the co-twin. II 159 The lengths of separation and contact of course also varied with age at study – older twins had more time either to be separated or in contact – which ranged from 19 to 68 years (…). (…) Bouchard fully expected that he would find that some individual characteristics would show genetic influences and others not. [He also] also expected that reared-apart twins would be distinctly less similar than reared-together twins, again more so for some characteristics than others. II 160 MISTRA has generated almost 200 scientific papers due to its extremely extensive assessment and long-running nature. (…) perhaps one stands out as having had particular impact on the field (…): The Minnesota Study of Twins Reared Apart’ (Bouchard, Lykken, McGue, Segal, & Tellegen, 1990)(2), published in Science in 1990. (…) it focused on genetic influences on IQ [and] it explored and compared reared-apart and reared-together twin similarity (…). The MISTRA [of this particular study] assessment included three independent measures of IQ. >Intelligence, >Intelligence tests, >Method, >Measurements. Findings: The first study results were intra-class correlations of these three IQ scores in the MISTRA MZ twins. In reared-apart MZ (MZA) twins who directly/formally share effectively no environmental influences, these correlations are optimal because they are especially for data organized in groups (…). II 161 They are direct estimates of the proportions of variance that can be attributed to genetic influence. Two were .78; the third was .69, with a mean of .75. It is suggested here that, assuming appropriateness of the assumption of no environmental similarity, genetic influences account for about 70% of population variance in IQ in adulthood. [Another possibility is that lacing separated twins in similar homes] could then induce similar behaviours and psychological characteristics in the twins. Separate indices of similarity of twins’ adoptive parent socioeconomic status (…) coupled with the associations between these home features and IQ, indicated not just no significant impact of placement similarity on IQ, but also measured its impact at effectively 0. II 162 Twins who had been reared together and remained in closer contact in adulthood had been observed to be more similar in some ways than those maintaining less (Rose & Kaprio, 1988)(3), but there was evidence in another reared-together sample that similarity did more to encourage contact than vice-versa (Lykken, Bouchard, McGue, & Tellegen, 1990)(4). The MISTRA contact data indicated no greater similarity with greater time together before separation, time apart to first reunion, total time, or percentage of lifetime spent apart. II 163 [The 1990 MISTRA study(2) also indicated that there is] substantial genetic variance on all the characteristics. They also, perhaps even more surprisingly, very often indicated that MZA twins are almost as similar as MZT twins, sometimes even as similar as the same person assessed twice within some rather short time-span such as a month (…).This suggested that neither common upbringing nor ongoing contact between family members does much to make them similar, at least in adulthood. II 164 [Another implication by Bouchard et al. (1990)(2) was that] MZA twins must be so similar because their basically identical genomes lead them to experience more similar environments. (…) environmental options and the experiences and lessons they offer more often accentuate and deepen genetic influence than dampen it. >Nature versus nurture. 1. Segal, N. L. (2012). Born together, reared apart: The landmark Minnesota twin study. Cambridge, MA: Harvard University Press. 2. Bouchard, T., Jr., Lykken, D. T., McGue, M., Segal, N. L., & Tellegen, A. (1990). Sources of human psychological differences: The Minnesota Study of Twins Reared Apart. Science, 250, 223–228. 3. Rose, R. J., & Kaprio, J. (1988). Frequency of social contact and intrapair resemblance of adult monozygotic co-twins – Or does shared experience influence personality after all? Behavior Genetics, 18, 309–328. 4. Lykken, D. T., Bouchard, T. J., Jr., McGue, M., & Tellegen, A. (1990). Does contact lead to similarity or similarity to contact. Behavior Genetics, 20, 547–561. Johnson, Wendy: “Genetic Influences on Behaviour Revisiting Bouchard et al. (1990)”, In: Philip J. Corr (Ed.) 2018. Personality and Individual Differences. Revisiting the classical studies. Singapore, Washington DC, Melbourne: Sage, pp. 155-170._____________Explanation of symbols: Roman numerals indicate the source, arabic numerals indicate the page number. The corresponding books are indicated on the right hand side. ((s)…): Comment by the sender of the contribution. Translations: Dictionary of Arguments The note [Concept/Author], [Author1]Vs[Author2] or [Author]Vs[term] resp. "problem:"/"solution:", "old:"/"new:" and "thesis:" is an addition from the Dictionary of Arguments. If a German edition is specified, the page numbers refer to this edition. |
Bouchard, Thomas J. Corr I Philip J. Corr Gerald Matthews The Cambridge Handbook of Personality Psychology New York 2009 Corr II Philip J. Corr (Ed.) Personality and Individual Differences - Revisiting the classical studies Singapore, Washington DC, Melbourne 2018 |
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> Counter arguments against Bouchard
> Counter arguments in relation to Twin Studies
