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Critically consider the role of genetic factors in the development of measured intelligence.

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Sophie Parslow                28/04/07

Critically consider the role of genetic factors in the

 development of measured intelligence.

Genetic factors are a major influence on the development of measured intelligence. However, extensive research suggests that genetic factors alone cannot account for a person’s intelligence. Research evidence suggests that a person’s intelligence isn’t ‘fixed’ from birth, but environmental and social factors can cause an increase in intelligence.

The importance of genetic factors in intelligence is exemplified in family resemblance studies. This involves examining the correlation of intelligence test scores among people who vary in genetic similarity. If genetic factors influence IQ then the closer the genetic relationship between two people, then the greater the correspondence rate (concordance) between their IQ’s should be. In Bouchard and Mcgue’s worldwide review of 111 studies, they found the closer the genetic relationship between individuals the higher the correspondence of IQ scores.  For example the correlation for cousins (who share 12.5 % of their genes) is weaker than that for parents and offspring who share 50 % of their genes. The strongest Correlation is for Monozygotic twins (identical twins) who share the same genes.Therefore,these findings suggest that genetic factors play a key role in measured intelligence. However, the main

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Furthermore research into adoption studies seems to prove genetics play a fundamental role in influencing intelligence. Adoption studies are useful in proving that genetic factors influence intelligence because children share half their genes with their biological parents but none of their environment, and their environment with adoptive parents but none of their genes. Musinger found that the correlation of IQ score for adopted children and biological parents was 0.48 compared to 0.19 for adopted children and adoptive parents. Therefore, in this study biological factors seem more important than environmental factors in determining intelligence. Moreover, Plomin found that IQ’s of adopted children and their unrelated siblings showed a weak correlation.  Thus proving that even though the children shared the same environment,  their intelligence differed because of their genetic differences.  

However a problem of adoption studies is assessing the similarity between biological parents and adoptive parent’s environments. Research by Scarr and Weinberg proves that when the environments of the biological and adoptive parents are very different a substantial change in IQ score can be observed. Scarr and Weinberg carried out a study of 101 white families that where above average in intelligence, income, and social class who adopted black children. If genetics are  the only

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In conclusion measured intelligence can be recognised as an interaction between genetic and environmental factors. Genes do not fix intelligence; instead they provide the basis of intellect. Environmental factors build on genetic intelligence, and as extensive research proves a stimulating environment can lead to an increase of IQ scores. The correlation between IQ scores and genetic similarity exemplifies that intelligence is mainly biologically based. However Intelligence is highly changeable and can be increased due to environmental factors. If both environmental and genetic factors influence intelligence then this causes the problem of how much each contributes. Heritability refers to how much a characteristic is determined by genetic factors within a particular population at a particular time. The heriabilty estimate of genetic factors in IQ is 80%  however more recently that has been decreased to 50/60%(Bouchard and Segal).  This makes is difficult to distinguish whether it is environmental factors of genetic factors that determine intelligence because they are closely linked. Moreover Bee’s research proves that children from higher educated, middle class families have children with higher IQ’s, however this could be because of environmental factors or genetic factors or both.

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