Research has shown that genetic inheritance strongly influences behaviour. One behaviour that is believed to have a strong genetic component is intelligence. Intelligence defined as the ability to acquire and apply knowledge. It is commonly tested through IQ tests and twin studies can be used to investigate the influence of genetic inheritance of this trait. Monozygotic twins (MZT) share 100% of their genes. Dizygotic twins (DZT) share around 50% of their genes. Researchers calculate concordance rates, which is the likelihood or probability that if one twin has the trait the other individual will also have it. The concordance rate is assumed to establish if or to what extent a certain trait is inherited.

This is supported by Bouchard et al (1990) who conducted a longitudinal study aimed to establish the extent to which intelligence is an inherited trait. The study used over 100 sets of MZT and DZT around the world, who were raised together and apart, to investigate concordance rates for a number of variables such as IQ. Researchers gave them approximately 50 hours of psychological and physiological testing.

The results indicated concordance rates for IQ were 86% for MZT reared together compared to 87% for the same person doing the test twice. Similarity rate between MZT reared apart was approximately 76%. This indicates that genetic inheritance has a large influence on intelligence as the concordance rates correlated positively with DNA match. However, the environment plays a role as the MZ twins raised apart had lower concordance rates than those raised together. Hence, Bouchard determined a heritability estimate of 70% of intelligence attributed to genetics and 30% to other factors in the surrounding environment.

Would this be better?