Furthermore, its measures was in criminality. Not all criminal offenses show aggressive behaviour such as stealing. Therefore, the findings validity is reduced.
Alike, twin studies fail to consider the environment and how it may impact the likelihood of twins carrying out aggression.
Therefore research was conducted on adoption and both accounts for the environment and genes. Mednick conducted research into children who were adopted and looked at the likelihood of them showing aggressive behaviour if biological or adopted parents had already. They found that children who had a biological parent who had a criminal conviction had a higher percentage of a conviction than adopted parents. This proves that it is genes that have the main influence of aggression not as much as the environment.
Supporting research was conducted by Holfling which showed similar results. They also found that biological parents who showed aggression were more likely to have a child with similar behaviour than an adopted parent. This provides support that it is biological factors that mainly influence aggression.
Another positive of these findings is that it does research within the nature/nurture debate. Adoption studies look at the environment at adopted house but also the biology of the biological parents. Therefore, these findings are very valid and useful and it’s easy to conclude that genes are the factor that impact aggression.
An alternative explanation was provided by Sandburg on XYY karyotype genes. They studies men who had the standard XY gene and those who had an extra Y gene and compared them for aggressive behaviour. They found that the extra gene was likely to contribute to them showing mate aggression. Concluding that having an extra Y karyotype means you will be more aggressive.
Supporting research is unclear as the majority of it is conducted on animals. For instance, nelson fund that through selective breeding, aggression was higher. This shows that aggression is passed through genes. However, humans are more complex than other animals and therefore, findings from animals cannot be generalised to humans as findings may differ.
Nevertheless, Theilguard conducted research on humans to find if there were any specific personality traits with people who had XYY genes. They did not find any differences apart from height between those with or without the extra gene.
Overall the approach is reductionistic. This is because it only focusses on the biological aspects and fails to consider any other approaches such as social approaches. Therefore, it doesn’t account for all factors that could contribute to aggression.
The approach is also deterministic. This is because it fails to consider free will. Not everyone shows aggression and therefore they have the free will to no be aggressive which this approach fails to consider.
Also, although adoption studies look at both, the approach favours nature rather than nurture. The biological approach only looks at biology and genes and no other factors like the environment which could also influence aggression.
In conclusion, the biological approach provides a clear explanation to how genes impact someone showing aggressive behaviour. However, it doesn’t only focuses on genes and no other approaches such as social. For instance, Bandura’s social learning theory suggests that aggression is caused not only by inherited factors but also environmental factors such as reproduction which is copying (aggressive) behaviour you have witnessed. Therefore, this approach doesn’t show aggression as a whole.