Behavioural genetics is the study of the effects of genes as well as well the environment on the behaviour of the individuals. The scientists who study the Behavioural genetics are known as behavioural geneticists.
In this case Dr. Hakim is studying the influence of genes and the environment on the aggression, which is a kind of behaviour. Hence, Dr. Hakim is a behavioural geneticists, and he works in in the field of behavioural genetics.
