Examining Genetic Influence On Intelligence

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Identical twin studies are most useful in determining genetic influence on intelligence. Since the identical twins share the same exact genes, the straightforward comparison of intelligence can display if this human trait is truly heritable. Similarity of intelligence scores between identical twins supports the genetic influence on intelligence. According to Myers (2007),
Across studies of 10,000 twins, the intelligence test scores of identical twins reared together are virtually as similar as those of the same person taking the same test twice…Likewise, the test scores of identical twins reared separately are similar enough to lead twin researcher Thomas Bouchard (1996) to estimate that ‘about 70 percent’ of intelligence score variation ‘can be attributed to genetic variation. (p. 455) As stated by Myers (2007), in the above quote, adopted twins studies also play a role in determining levels of intelligence and its heritability. However, like in all other psychological testing, correlation does not always mean causation and atypical findings may find their way into the data poll. It must also be noted that in order to successfully foster an identical twin study, all the twins should be adopted. This provides for a better chance for the twins to grow up in a different environment from their biological parents. If this is not the cases, how can professionals determine that environmental influences are not the cause of the intellectual levels? In addition, if separated,
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