Definition
Testosterone is a steroid hormone produced mainly in the testes and, in smaller amounts, the ovaries and adrenal glands. It is popularly cast as the molecule of male aggression — and that, Sapolsky insists, is a myth that survives because it is convenient, not because it is true.
The accurate picture is subtler. Testosterone does not implant aggression in a brain that lacked it. It amplifies behavioral tendencies that are already present, and what it amplifies is better described as status-seeking than violence. In a context where status is won through cooperation or generosity, higher testosterone can promote exactly those behaviors.
Why it matters
How it works
Testosterone crosses cell membranes and binds intracellular receptors that alter gene expression, including in brain regions like the amygdala that weigh threat and reward. It can make the amygdala more reactive to social challenge — but whether that reactivity becomes a fight, a competition, or a charitable display depends entirely on the situation and on what the individual has learned to do.