PassingPsych

Genetic similarities refer to the proportion of genes or DNA that is shared between populations. Genes carry information that determines your traits, which are features or characteristics that are inherited from your parents. By examining individuals or animals that share a high proportion of DNA with us, we can understand the potential role of genetics on behaviour. For instance, if we share a high proportion of genes and exhibit the same behaviour, there is a higher likelihood of this behaviour being genetic. Twin research is based on a systematic analysis of the similarities between Monozygotic twins (MZ twins) and Dizygotic twins (DZ twins), with the assumption that there is more concordance (the rate at which behaviour is exhibited among those who share a higher percentage of genes) between MZ and DZ twins, and lower for siblings. In this essay, I will provide a detailed account of the potential role of genetic similarities on behaviour using the supporting study of Caccaro et al.

Caccaro et al aimed to investigate the heritability of aggression and irritability in MZ and DZ twins. To investigate, they conducted a quasi-experiment involving MZ and DZ twin pairs recruited from the Vietnam Era Twin (VET) Registry. The VET Registry consists of 7,375 American veteran male-male twin pairs born between 1939 and 1955 who served in the Armed Forces of the United States between 1964 and 1975. Surveys were sent to individuals on the registry, and 796 (65.9%) responded. Of the 796 individuals who participated, 628 were members of a twin pair. The Buss-Durkee Hostility Inventory (BDHI) is a 75-item questionnaire designed to assess different types of hostile behaviour. Four subscales of the BDHI were used in the present study to assess aggressive behaviour (direct, indirect, verbal assault, and irritability). The results showed that MZ twin pairs had 50% concordance, whereas DZ twins had only 19%. They estimated that genes account for approximately 50% of individual differences in aggression.

Caccaro et al demonstrate the effect of a high proportion of genetic similarities in twins on aggressive behaviour. For example, MZ twins have a higher concordance rate than DZ twins. This is significant because MZ twins share 100% of their genetics with each other, and their rate of aggression was higher than DZ twins, who share 50% of their genetic information. This increased the chances that the aggressive behaviour has a genetic root. Therefore, genetic similarities do have an effect on human behaviour.