Behave: The Biology of Humans at Our Best and Worst

by Robert M. Sapolsky

This is a central point of this book—we don’t hate violence. We hate and fear the wrong kind of violence, violence in the wrong context. Because violence in the right context is different. We pay good money to watch it in a stadium, we teach our kids to fight back, we feel proud when, in creaky middle age, we manage a dirty hip-check in a weekend basketball game. Our conversations are filled with military metaphors—we rally the troops after our ideas get shot down.

this is a book that is rooted in science, specifically biology. And out of that come three key points. First, you can’t begin to understand things like aggression, competition, cooperation, and empathy without biology; I say this for the benefit of a certain breed of social scientist who finds biology to be irrelevant and a bit ideologically suspect when thinking about human social behavior. But just as important, second, you’re just as much up the creek if you rely only on biology; this is said for the benefit of a style of molecular fundamentalist who believes that the social sciences are destined to be consumed by “real” science. And as a third point, by the time you finish this book, you’ll see that it actually makes no sense to distinguish between aspects of a behavior that are “biological” and those that would be described as, say, “psychological” or “cultural.” Utterly intertwined.

But that’s not what we’re interested in. Instead, it’s human behavior, human social behavior, and in many cases abnormal human social behavior. And it is indeed a mess, a subject involving brain chemistry, hormones, sensory cues, prenatal environment, early experience, genes, both biological and cultural evolution, and ecological pressures, among other things.

And you’re also saying, “. . . because of the gene that codes for the particular version of neurochemical Y.” And if you’ve so much as whispered the word “gene,” you’re also saying, “. . . and because of the millennia of factors that shaped the evolution of that particular gene.” And so on. There are not different disciplinary buckets. Instead, each one is the end product of all the biological influences that came before it and will influence all the factors that follow it. Thus, it is impossible to conclude that a behavior is caused by a gene, a hormone, a childhood trauma, because the second you invoke one type of explanation, you are de facto invoking them all. No buckets. A “neurobiological” or “genetic” or “developmental” explanation for a behavior is just shorthand, an expository convenience for temporarily approaching the whole multifactorial arc from a particular perspective.

We can be passive-aggressive, damn with faint praise, cut with scorn, express contempt with patronizing concern. All species are unique, but we are unique in some pretty unique ways.

A behavior has occurred—one that is reprehensible, or wonderful, or floating ambiguously in between. What occurred in the prior second that triggered the behavior? This is the province of the nervous system. What occurred in the prior seconds to minutes that triggered the nervous system to produce that behavior? This is the world of sensory stimuli, much of it sensed unconsciously. What occurred in the prior hours to days to change the sensitivity of the nervous system to such stimuli? Acute actions of hormones. And so on, all the way back to the evolutionary pressures played out over the prior millions of years that started the ball rolling.

But the biggest reason for the definitional challenge was emphasized in the introduction—these terms mean different things to scientists living inside different disciplines. Is “aggression” about thought, emotion, or something done with muscles? Is “altruism” something that can be studied mathematically in various species, including bacteria, or are we discussing moral development in kids? And implicit in these different perspectives, disciplines have differing tendencies toward lumping and splitting—these scientists believe that behavior X consists of two different subtypes, whereas those scientists think it comes in seventeen flavors.

The brain is the final common pathway, the conduit that mediates the influences of all the distal factors to be covered in the chapters to come. What happened an hour, a decade, a million years earlier? What happened were factors that impacted the brain and the behavior it produced.

Limbic function is now recognized as central to the emotions that fuel our best and worst behaviors, and extensive research has uncovered the functions of its structures (e.g., the amygdala, hippocampus, septum, habenula, and mammillary bodies).

The hippocampus decides whether a factoid is worth filing away, depending on whether the amygdala has gotten worked up over it.

Motor outputs. There’s a second shortcut regarding the amygdala, specifically when it’s talking to motor neurons that command movement.30 Logically, when the amygdala wants to mobilize a behavior—say, fleeing—it talks to the frontal cortex, seeking its executive approval. But if sufficiently aroused, the amygdala talks directly to subcortical, reflexive motor pathways. Again, there’s a trade-off—increased speed by bypassing the cortex, but decreased accuracy.

When is the sympathetic nervous system going full blast? During fear, flight, fight, and sex. Or if you’ve won the lottery, are happily sprinting down a soccer field, or have just solved Fermat’s theorem

the most important theme is the amygdala’s dual role in both aggression and facets of fear and anxiety. Fear and aggression are not inevitably intertwined—not all fear causes aggression, and not all aggression is rooted in fear. Fear typically increases aggression only in those already prone to it; among the subordinate who lack the option of expressing aggression safely, fear does the opposite. The dissociation between fear and aggression is evident in violent psychopaths, who are the antithesis of fearful—both physiologically and subjectively they are less reactive to pain; their amygdalae are relatively unresponsive to typical fear-evoking stimuli and are smaller than normal.

Its list of expertise includes working memory, executive function (organizing knowledge strategically, and then initiating an action based on an executive decision), gratification postponement, long-term planning, regulation of emotions, and reining in impulsivity.35

The frontal cortex is the last brain region to fully mature, with the most evolutionarily recent subparts the very last. Amazingly, it’s not fully online until people are in their midtwenties. You’d better bet this factoid will be relevant to the chapter about adolescence.

So the frontal cortex is awash in Calvinist self-discipline, a superego with its nose to the grindstone.48 But as an important qualifier, soon after we’re potty-trained, doing the harder thing with our bladder muscles becomes automatic. Likewise with other initially demanding frontal tasks.

And that’s when doing the trill is transferred from the frontal cortex to more reflexive brain regions (e.g., the cerebellum). This transition to automaticity also happens when you get good at a sport, when metaphorically your body knows what to do without your thinking about it. The

Among humans, the larger someone’s social network (measured by number of different people texted), the larger a particular PFC subregion (stay tuned).

The differences appear when it comes to making social/emotional decisions—vmPFC patients just can’t decide.* They understand the options and can sagely advise someone else in similar circumstances. But the closer to home and the more emotional the scenario, the more they have problems.

Damasio has produced an influential theory about emotion-laden decision making, rooted in the philosophies of Hume and William James; this will soon be discussed.61 Briefly, the frontal cortex runs “as if” experiments of gut feelings—“How would I feel if this outcome occurred?”—and makes choices with the answer in mind. Damaging the vmPFC, thus removing limbic input to the PFC, eliminates gut feelings, making decisions harder.

Antecedent reappraisal is why placebos work.69

“My finger is about to be pricked by a pin, but this cream will block the pain.” The PFC activates, blunting activity in the amygdala and pain circuitry, as well as pain perception.

Wegner demonstrated a two-step process of frontocortical regulation: (A) one stream identifies X as being very important; (B) the other stream tracks whether the conclusion is “Do X” or “Never do X.” And during stress, distraction, or heavy cognitive load, the two streams can dissociate; the A stream exerts its presence without the B stream saying which fork in the road to take. The chance that you will do precisely the wrong thing rises not despite your best efforts but because of a stress-boggled version of them.