Behave is an excellent book.
The main biological point is “it’s complicated”, which is a great lesson to leave behind when temptingly over-simplified answers abound.
I really liked the structure of the first half, tracing back a behavior to what happened milliseconds before (in the world of neurotransmitters) to hours before (hormones) to in childhood (development) to millions of years ago (evolution).
One idea emphasized was that natural selection often selects on patterns of gene regulation, not the genes themselves. So, instead of thinking of “a gene for” any given phenotypic trait, it makes more sense to think of interactions. I already knew about polygenic traits (those where multiple genes combine to express an effect), but this takes that further. Instead, we have loops of genes for proteins that help build hormones that regulate other genes which code for RNA strands that interfere with other RNA that codes for enzymes that splice DNA differently and loops and loops and loops. Sheer mountains of complexity. It was really cool to scrape the surface of the complexity of some exploratory science, since my usual thinking (generally about computers/math) is all about human-created (or -simplified) ideas, typically designed to be relatively straightforward.
The often extremely-context-dependent nature of behavior struck me as well. For example, while I knew that oxytocin fosters “good feelings” with those you’re close to, I didn’t know it essentially does the opposite for interactions with the outgroup. Neuroplasticity is even more important than I previously thought (some parts of the brain are left relatively untouched by genes in favor of being shaped by learning), and mirror neurons maybe a little less so.
Then there’s the stuff on free will and criminal justice. I knew of Sapolsky’s takes on these from watching a couple lectures of his years back, but it was super interesting to learn more details behind his thinking on these topics. Essentially, he’s a complete free will denier. Sapolsky does give a brief nod to the “narrow philosophical notion” of compatibilism, which is probably the label I’d use for myself if I had to, but in the sense of “free will” that’s used in Behave, I am also a complete denier. The last few paragraphs of the free will chapter outline the difficulty in not assigning anyone the true credit for their actions (although I notice Sapolsky left his own name on the front of the book). This is why I find compatibilism (in the strict, narrow sense) compelling. I do think it’s philosophically allowable (and even useful) to have something that is “a person”, as opposed to just describing the universe as one coherent whole, responsible for everything that happens within it, because the networks of causality are so intertwined. However, I don’t think that most people’s thinking on free will as directly/entirely compatible with how our universe works makes that much sense. As Sapolsky repeatedly says, that’s a form of inventing a homunculus and placing it in an ever-shrinking box. However, though he doesn’t delve into the direct underlying philosophy too much, I think Sapolsky might be making a mistake in the other direction, towards a kind of biological fatalism.
Consider this quick thought experiment on causality: raise your right hand. Did you just make a choice? Did you just cause the prior state of the universe to be such that you would raise your hand? Was such an action also possible if we assume this universe were completely deterministic, causes giving rise to direct effects all the way down? I would argue: yes, you made a choice (in a certain, narrower-than-usual sense), no, you didn’t cause the universe (the universe caused you), and yes, there’s nothing about raising your hand just then that couldn’t have happened in a clockwork universe. Choices, the logical direction of causality, and determinism can coexist. Of course, if you ignored me and didn’t raise your hand, that’s also a choice which the universe led to, determined by prior causes.
I think my main reaction to Sapolsky’s idea of abolishing the current justice system was tempered by the immediate intuition of “whoa, that’s extreme”, but there definitely seems to be something there to think about.