In Brendgen's study, what type of aggression had a higher correlation between the ratings of MZ twins?

In Brendgen's study, the higher correlation between the ratings of monozygotic (MZ) twins for physical aggression suggests a significant genetic influence on this type of aggressive behavior. MZ twins share 100% of their genetic material, which allows researchers to examine the impact of genetics versus environment on behavior. The strong correlation for physical aggression indicates that this type of aggression may be more strongly inherited than other forms.

Physical aggression manifests as overt acts directed at others and can be more easily observed and rated compared to more subtle forms of aggression, like social or emotional aggression. The study's findings highlight how genetic predispositions can shape aggressive behavior tendencies, particularly in the context of physical confrontations, while other types, such as social or verbal aggression, may involve greater environmental influences or learned behaviors.