Summary
We read Behave after reading Determined earlier in the year. I think reading Behave first would make more sense. It goes very deeply into the science that is used to justify much of the conclusions in Determined. I highly recommend reading both books. The most compassionate that I’ve felt in my life towards all my fellow humans has been after the boost that comes after reading both of these books.
Sapolsky structures the first half of Behave around the idea of a single act of behavior (perhaps good or perhaps evil) and then walks backward in time asking, “What was happening just before this, and before that?” The central thesis is basically the same as the one he makes in Determined, which is that there is no single cause for why we behave well or badly, but there are definitely deterministic causes. Everything is context, and levels of explanation are nested rather than competing. Neurons, hormones, development, genes, culture, and evolution are all partial stories that start to make sense when taken together.
He opens with vivid moral examples. A central theme introduced early in the book is that the same motor act can be “good” or “evil” depending on context: pulling a trigger can be murder or heroism. What matters is not the muscles moving but the meaning of those movements in a particular situation. Where Determined focuses more on philosophical arguments, Behave goes more deeply into the neurobiology supporting those arguments.
Each level of causation offers new information about propensities and vulnerabilities. So while a phrase like, "this hormone causes aggression" or "this gene makes you violent" is too simplistic, they do increase the probability of certain behaviors under certain conditions.
In the second chapter, Sapolsky begins exploring what happens biologically one second before a behavior is executed. Here we learn about how different neural circuits provide information that help make decisions about appropriate actions. The big circuits that he focuses on are circuits devoted to processing threat and arousal, reward and motivation, and regulation and constraint, which act together to create meaning and predictions for different contexts. He also introduces the theme of neuro-fetishism, which is the urge to take something about behavior or experience more seriously if we can observe it in the brain.
From here, we go slightly further back in causal time with each chapter. Chapter 3 explores seconds to minutes before, and explores how sensory cues and prior predictions, priming, and culture affect our current states. Chapter 4 explores hours to days before, and mostly focuses on our hormonal milieu. He focuses mostly on testosterone and aggression and oxytocin/vasopressin and prosociality, discussing the limits and truths of the influence of both on behavior. Chapter 5 explores days to months before and is mostly about experience-dependent plasticity. Repeated stress, learning or conditioning remodels neural circuits, which shapes how a current cue is processed in the moment. He focuses particularly on pairing cues with rewards or punishments, and the effect of chronically elevated stress.
In chapters 6-8, Sapolsky discusses developmental effects. Chapter 6 explores the lasting effects of adolescence. It offers both a sympathetic view of adolescent behavior specifically, by discussing the transient reconfiguration of neural circuitry that leads to a strong drive for novelty and risk combined with immature prefrontal control. But also, this is a period of time where patterns that become stable personality later begin to crystallize through pruning and myelination, and so is an extremely important neurodevelopmental period. Chapter 7 goes even further back to the effect of early childhood and even prenatal life - where he talks about how maternal stress, nutrition, and caregiving quality have an outsized impact on shaping the initial development of circuits involved especially in regulation and threat detection and have long-lasting impacts on our behaviors. Chapter 8 continues this to the very begin of development, discussing genetics and epigenetics. We've discussed this topic extensively in the past couple of years, and Sapolsky emphasizes those same lessons - the genetics don't determine complex traits, but are also strongly involved - usually by combinations of large networks of genes that interact with environmental contexts and random development. He also discusses how complex behaviors can be passed down through epigenetics which modify which genes are active.
Finally, Chapter 9 goes back to explore how history influences your behavior, even before you were born. This chapter is focused mostly on culture, focusing on norms, sex differences, and longstanding political and economic structures in those cultures. Chapter 10 closes this exercise in working backwards through time by discussing broader concepts of the evolution of behavior, and then moves outward to discuss group behavior, how we create meaning, and consequences. So these early chapters are more about why a behavior occurred and the later chapters are more about what it means that the behavior occurred, and what follows ethically, politically, and institutionally. The second half is a much more integrative synthesis and delves more into moral philosphy.
Chapter 10 on evolution and Chapter 11 on “Us versus Them” form the hinge between the two parts of the book. By this point, Sapolsky has already dismantled any simple nature-versus-nurture story. Now he shows that the roots of many of our most troubling social behaviors emerge from adaptations for group living. The same biology that enables cooperation, trust, and altruism also makes us exquisitely sensitive to group boundaries. In-group favoritism and out-group hostility are features that once conferred survival advantages. The danger, Sapolsky emphasizes, is that modern humans have inherited Stone Age social circuitry while wielding industrial-scale power.
From there, the book turns to hierarchy, obedience, and resistance. Sapolsky discusses how bad behavior is sometimes the predictable outcome of stress, status, and context. Hierarchies are biologically ancient, and rank shapes physiology, cognition, and risk-taking in ways that are often invisible to the people inhabiting them. I found it really interesting to learn how about how different positions in a hierarchy predispose people to behave in certain ways. In fact, one of the consistent themes that keeps emerging in the second half of the book is that a lot of our moral behavior and judgements are happening beneath conscious thought. Obedience to authority can lead to terrible acts in groups when responsibility is diffused, norms are slowly escalated, and victims are rendered abstract. Resistance, crucially, appears when those same mechanisms are disrupted: when authority is delegitimized, when empathy is restored, or when moral responsibility is made more concrete.
This all sets the stage for Sapolsky’s treatment of morality itself. Once again, rather than presenting morality as a rational system we consult, he portrays it as a set of intuitions generated rapidly by emotional and social circuitry, with reasoning arriving afterward to justify the verdict. Moral consistency turns out to be quite rare. Humans are capable of profound compassion, but that compassion is sharply bounded by group membership, proximity, and framing. We are actually better about abstract moral reasoning around moral issues that are very distant from us because our moral-emotional circuitry is highly influenced by proximity. The unsettling implication is that morality is deeply contingent. Pro-social behavior improves not simply through better arguments, but by hacking our internal moral architecture, such as widening who counts as “us” by focusing on similarities.
Empathy, in the following chapter, is similarly demystified, but also made more complex. Sapolsky draws careful distinctions between feeling someone’s pain, cognitively understanding it, and acting to alleviate it. Feeling too much of someone else's pain can actually incapacitate or lead to withdrawal but feeling too little can lead us dehumanize others. The biology of caregiving turns out to depend less on shared suffering than on autonomic physiological states that allow calm, regulated engagement. Compassion, in this view, is not an overflow of emotion but a skillful balance between emotional resonance and parasympathetic activation.
Language then enters the picture as a biological force in its own right in humans. Metaphors actually matter a lot. They activate neural frameworks that shape how problems are perceived and what solutions feel appropriate. When groups are described as diseases, vermin, or floods, extermination begins to sound like hygiene. Or describing something like a beast or a virus invokes solutions of hunting vs. prevention.
All of this culminates in Sapolsky’s most provocative move, which is basically the same as his next book Determined. He applies the full causal weight of biology to criminal behavior and free will. If every action is the product of genes, development, context, and neurobiology, traditional notions of blame and the desire for retributive punishment don’t really make sense. Sapolsky argues for a justice system oriented toward public safety, rehabilitation, and harm reduction rather than retribution. Responsibility shifts from moral condemnation of individuals to collective responsibility for the conditions that shape behavior.
The final chapter on war and peace widens the lens one last time. War is neither inevitable nor aberrant. It is a cultural institution that exploits evolved tendencies under particular conditions: scarcity, hierarchy, propaganda, and dehumanization. Just as importantly, large-scale peace is also a biological and cultural achievement, arising when interdependence, shared identity, and stable institutions dampen our worst impulses.
By the epilogue, Sapolsky has arrived at a position that is neither really optimistic nor fatalistic. I think it is mostly relativistic. The biology he examines throughout the book, and especially our tendency to trick ourselves about our own moral reasoning demands humility. The same biological forces that make humans cooperative also can lead to harm. Behave is ultimately an argument that understanding the causes of behavior should reframe our moral commitments from punishment to prevention and from individual virtue to collective design.
Discussion Questions
- After reading Part I, to what extent did you find your own tendencies toward moral judgment softened? Do you feel more compassion, more fatalism, or something else when you look at “bad behavior” through this multi-layered lens? How do you feel generally after reading the first half?
- Sapolsky criticizes the idea that we only take conditions seriously when there is a brain scan. In your own life experience, have you seen or used neuroscience used to legitimize suffering that “should” have been believed anyway, and do we have alternative ways to confer legitimacy.
- If we take Sapolsky seriously that neurons, hormones, development, genes, and culture are all partial stories, it seems like there should be some way of connecting all of those things that comes closer to making better predictions around behavior. I wonder if anyone is trying to link them together, or what that would look like?
- Given the evidence that seconds-scale sensory primes and internal states heavily bias choices, what remains of the intuitive notion of a conscious, rational “moment of decision”? Does this change how we think about responsibility? Do you think we could prime criminals to act better? Like if we are being mugged, do you think that using the right words like spells could lead to better outcomes?
- The chapters on prenatal and early life effects highlight sensitive periods and epigenetic embedding of adversity. Given the difficulty of changing early environments at scale, what kind of interventions seem most realistic? What would be the best use of resources to improve early development?
- Sapolsky pushes a strongly probabilistic view of behavioral genetics. Do you think that genetic tools, like polygenic scores which combine many genes to determine risk, are more likely to reduce stigma through nuance or to fuel new forms of essentialism?
- Sapolsky talks about the nuances of hormones. How do you think neuroscientists should engage with media narratives that oversimplify hormones as “aggression chemicals” or “love chemicals”? Do you think correcting these narratives actually matters for behavior or policy?
- I have some friends who pay a lot of attention to power dynamics and social hierarchies. Before discussing it with them, I never really paid too much attention to that in groups. I'm curious where others fall on that spectrum. What aspects of power do you pay attention to?
- If every behavior has a biological cause, what does it even mean to hold someone morally responsible? Where do people in the group feel the strongest emotional resistance to Sapolsky’s argument?
- Sapolsky argues that context routinely overwhelms character. Can you think of cases where this feels obviously true, and cases where it feels deeply unsatisfying or even dangerous to accept?
- Is it psychologically realistic to expect humans to have moral concern for large, abstract groups? If not, what does that imply for modern politics, climate change, or global justice? What do you think is the best way to cultivate large-scale actions that support large groups.
- Sapolsky suggests that punishment is largely ineffective at deterrence. Do you agree with this? Is punishment really just one thing or is it many things?
- Empathy can backfire, leading to burnout, paralysis, or bias. Have you seen cases where “feeling someone’s pain” made a situation worse rather than better?
- Language shapes violence long before violence occurs. Have you noticed any metaphors in our current public discourse that might be quietly priming harm or shaping our solutions?
- If moral intuitions are fast and emotional, what role should reasoning play in ethical decision-making? Is reasoning mainly corrective, justificatory (convincing others and yourself), or performative?
- Do you think Sapolsky’s framework makes social change more likely or less likely? Does understanding causality motivate action or invite resignation?