Discuss the role of genetics in the development of measured intelligence

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Clive Newstead

Discuss the role of genetics in the development of measured intelligence (24 marks)

Genetic explanations of measured intelligence would suggest that intelligence is innate and hereditary, so we are predisposed to have the IQ that we have. One method of investigation into the role of genes is twin studies. Since monozygotic twins share 100% of their genes, it follows that if measured intelligence is entirely a result of genetic causes, then monozygotic twins will have the same IQ. Bouchard & McGue conducted a meta-analysis of many studies into the role of genetics in intelligence, and found a strong correlation between the IQ of identical twins raised together and apart (0.86 and 0.72, respectively). Even the twins raised apart had a higher correlation between their IQ than did fraternal twins raised together (0.62). This does indicate a genetic link, but since the research is correlational, it is impossible to infer causation. Twins raised together share a similar environment and, especially in the case of identical twins, may be treated similarly; this could have an effect on their cognitive development, and their consequent IQs are likely to be similar. Additionally, those raised apart are likely to have been put up for adoption by their biological parents, and it is likely that similar types of families would adopt them, so even though the same environment is not shared, a similar one is. Furthermore, since the correlation for the identical twins is not 100%, it would follow that there must be environmental factors involved.

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Another method for studying the role of genetics is adoption studies. The Colorado Adoption Project is an ongoing longitudinal study of children separated from their biological parents in their first month of life; Plomin et al. found that, as these children get older, their intelligence becomes more and more like that of their biological parents and less like that of their adoptive parents. This indicates that biological factors are significant, but have a latent effect. This finding is duplicated by the Texas Adoption Project, which found no correlation between adopted children and their unrelated siblings by the age of 18. Thus, ...

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