Definition
Aggression is behavior intended to cause harm. It spans physical violence, threat, and coercion, and it appears in defensive, predatory, reactive, and instrumental forms. The intent to harm is what unites these otherwise different acts.
Sapolsky's central claim is that aggression has no single cause. It is the joint product of what happened a second before — in the brain — and what happened seconds, hours, years, and generations before that. Treating aggression as one thing with one explanation is, for Behave, the core mistake to avoid.
Why it matters
How it works
To explain a violent act, Sapolsky asks what shaped it across many timescales: the neural activity moments before, the sensory triggers and hormone levels seconds to hours before, the developmental and adolescent history years before, and the cultural and ecological context generations before. Each layer constrains the next.
This means no factor acts alone. Testosterone, for example, does not generate aggression on its own — it heightens the drive to defend status, and whether that shows up as violence depends entirely on context. The lesson is that aggression must be explained as a convergence of causes, not as a thing with a cause.