How can inherited traits and early family environments reinforce aggressive behaviour across generations of mice?

In mice, the reinforcement of aggressive behaviour across generations results from a complex interaction between inherited genes and early environmental experiences.1

Genetic and Environmental Interplay

Aggression is not solely instinctive; it is shaped by how an animal's genetic makeup interacts with its environment. Genetic factors, particularly those on the Y chromosome, influence early hormone secretion and sensitize brain regions to testosterone. Selective breeding studies confirm that these genetic predispositions can be passed down, creating distinct aggressive or nonaggressive strains.1

Generational Reinforcement

The environment can amplify these inherited traits through a cycle of behavior:
* Maternal Influence: Female mice from aggressive strains tend to handle their pups roughly. Consequently, offspring inherit genes predisposing them to aggression and simultaneously experience an aggression-promoting environment early in life.1
* Developmental Conditions: Beyond maternal care, prenatal factors—such as an embryo's position in the uterus—can expose developing mice to varying levels of androgens, which permanently organize brain structures to be more or less sensitive to aggression-facilitating hormones later in life.12

This continuous feedback loop ensures that both biological inheritance and early social context contribute to the persistence of aggressive behaviour.1