... (identical twins) who share the same genes.Therefore,these findings suggest that genetic factors play a key role in measured intelligence. However, the main criticism of these findings is that as the genetic similarity between people increases so does the similarity of their environment: for example parents and offspring usually live in the same household, cousins tend not to. Therefore, to overcome this problem of determining whether is was the environment or genetic factors that influenced the person's IQ score, research has been conducted in comparing the IQ score of MZ twins that are reared together in the same environment and those raised separately in different environments. Mz twins reared together showed a greater correlation of IQ than those reared apart, which shows that the environment plays an important role in influencing intelligence. However the fact that Mz's reared separately have a higher correlation of IQ scores than DZ (non identical) twins ...

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