How does hormone exposure early in development create long-lasting effects on aggression?

Hormone exposure during early development influences adult aggression through long-term organizational effects on the brain, rather than the reversible, short-term activational effects seen in adulthood.1

During critical prenatal and postnatal periods, a surge of steroid hormones—such as androgens—affects the development of specific brain structures that regulate aggressive behavior. This early exposure sensitizes these neural regions, making them more responsive to the aggression-facilitating effects of testosterone later in life.1

This process can lead to significant natural variation in aggression within the same species. For example, in mice, the hormonal environment within the uterus—influenced by the proximity of neighboring embryos—can dictate future behavior. Male embryos exposed to relatively low androgen levels remain less aggressive as adults, while female embryos exposed to high androgen levels may exhibit increased aggression when treated with testosterone later. Additionally, early exposure to non-gonadal hormones, such as AVP, has also been shown to increase adult aggression.1

Ultimately, these developmental hormonal influences interact with an individual's genetic makeup and postnatal environment to shape the complex, long-lasting neural pathways that control aggressive responses.12