To explain any behavior, you have to zoom out in stages

Sapolsky's organizing method is to take a single behavior — say, pulling a trigger, or reaching out to comfort someone — and ask what caused it at successively larger timescales: what fired in the brain one second before; what hormones were active in the preceding minutes and hours; what developmental and adolescent experiences shaped the relevant brain circuits years before; what happened in the womb and in early childhood; what genes were involved; what cultural norms were absorbed over a lifetime; and finally what evolutionary pressures shaped the whole species over millions of years.

His point is that isolating any one layer — "it's genetic," "it's cultural," "it's just his upbringing" — gives a false sense of a clean explanation. Every layer interacts with every other: a gene's effect depends on the environment expressing it, a hormone's effect depends on the social context it's released into, and a cultural norm gets absorbed into an already biologically primed brain.

This framework isn't just an organizing gimmick for the book — it's Sapolsky's actual argument about how causation works in biology generally.

Takeaway: whenever someone offers a single-cause explanation for behavior, ask what layer they left out.