Sapolsky builds a beast of a tome around one gimmick and it's brilliant: a person does something, an act of aggression or kindness, and he asks why do we do the things we do, then rewinds. One second before, what parts of the brain lit up in the second before an action, the lizard-ish amygdala, or the primate-y frontal cortex. Seconds to minutes, what sensory information obtained in the past few seconds to minutes primed you, the subliminal, unconscious cue you never noticed. Hours to days, what hormones were secreted, testosterone getting its bum rap, which he insists does not do what you think.

Then back to what happened in the years before, say during adolescence or childhood, or in the prenatal period, then genes, then what cultural forces in the last few hundred years shaped the behavior and how evolution in the last thousands of years influence behavior, each chapter one more zoom out on the same instant. Fair warning, I ended up starting with the appendix to read the basics of neurology and endocrine system, because without them much of this is very hard for anyone who doesn't have a degree in biology, and even those three primers may not get somebody up to speed if they've never taken a neuroscience course.

I came for the neuroscience and stayed for the voice, the charm and humour that Sapolsky shows as a lecturer shines through in his prose, kind, wise, eloquent, a great teacher with a rich, self-deprecating humor, and be sure to read all footnotes because the humorous footnotes are half the comedy album. He lets us know what he really thinks, wears his politics and his atheism and his discomfort with free will right on his sleeve, which some readers hate and I loved. The testosterone chapter is peak entertaining myth-busting, the hormone doesn't cause aggression so much as amplify whatever status seeking your culture already rewards, in a monastery it would make you competitively generous, and when he writes "Warrior gene" my ass you laugh out loud.

The us versus them material, the ways we're predisposed to think about others specifically in groups and out groups, is a case where Us vs. Them is a powerful influence in behavior, and it is used to manipulate people as well, the most useful and the most alarming stretch, right down to the deliberate dehumanization of outgroups. Now the niggle some readers cannot forgive: the book appears to lack a central thesis except that "it's complicated." Nothing seems to cause anything, instead everything just modulates everything else, and after so many ifs and maybes a couple of reviewers I trust would have preferred if he had stuck to things that were more clearly true. It did not bother me, that's probably closer to the truth than the endless internet debates over nature vs nurture, but go in knowing. Practical note, have a highlighter handy, be willing to dog-ear copiously, go back and reread when you feel lost, and don't feel obligated to learn it all, be glad to just retain the gist of it all, nobody holds the whole thing.

As an ambitious book that seeks to explain human behavior at almost every level of abstraction, why humans do the things we do, kind and cruel and tribal and heroic across every timescale at once, it's a massive undertaking, yet somehow Sapolsky managed to wrap it up nice and neat in a complex but fully comprehensible book, and it imparts ideas of enormous complexity without losing us. It changed a little of how I see myself and my fellow humans, since how we act is not just a matter of our individual character or free will but is governed by a thousand things, biological, social, economic, ideological and so on, and left me slightly vertiginous about agency, the way it squishes the concept of free will while encouraging compassionate and courageous action. Impressive and imposing, funny and witty, humane, too long, worth it.