Behave: The Biology of Humans at Our Best and Worst

by Robert M. Sapolsky

the brain region most involved in feeling afraid and anxious is most involved in generating aggression.

human amygdala preferentially responds to fear-evoking stimuli,

In PTSD sufferers the amygdala is overreactive to mildly fearful stimuli and is slow in calming down after being activated.

the amygdala isn’t about the pleasure of experiencing pleasure. It’s about the uncertain, unsettled yearning for a potential pleasure, the anxiety and fear and anger that the reward may be smaller than anticipated, or may not even happen. It’s about how many of our pleasures and our pursuits of them contain a corrosive vein of disease.fn22

the frontal cortex makes you do the harder thing when it’s the right thing to do.

the fact that winning stimulates testosterone secretion, which increases glucose delivery and metabolism in the animal’s muscles and makes his pheromones smell scarier.

making people do the easier thing when it’s the dumb-ass thing to do.7 Testosterone does this by decreasing activity in the prefrontal cortex and its functional coupling to the amygdala and increasing amygdaloid coupling with the thalamus—the source of that shortcut path of sensory information into the amygdala. Thus, more influence by split-second, low-accuracy inputs and less by the let’s-stop-and-think-about-this frontal cortex.

while the acute stress response involves enhanced immunity, chronic stress suppresses immunity, increasing vulnerability to some infectious diseases.fn29

Stress can disrupt cognition, impulse control, emotional regulation, decision making, empathy, and prosociality.

Oxytocin and vasopressin facilitate mother-infant bond formation and monogamous pair-bonding, decrease anxiety and stress, enhance trust and social affiliation, and make people more cooperative and generous. But this comes with a huge caveat—these hormones increase prosociality only toward an Us. When dealing with Thems, they make us more ethnocentric and xenophobic. Oxytocin is not a universal luv hormone. It’s a parochial one.

First, no part of the adult brain is more shaped by adolescence than the frontal cortex. Second, nothing about adolescence can be understood outside the context of delayed frontocortical maturation. If by adolescence limbic, autonomic, and endocrine systems are going full blast while the frontal cortex is still working out the assembly instructions, we’ve just explained why adolescents are so frustrating, great, asinine, impulsive, inspiring, destructive, self-destructive, selfless, selfish, impossible, and world changing. Think

Exposing children to a violent TV or film clip increases their odds of aggression soon after.41 Interestingly, the effect is stronger in girls (amid their having lower overall levels of aggression).

exposure does not remotely guarantee increased aggression—instead, effects are strongest on kids already prone toward violence. For them, exposure desensitizes and normalizes their own aggression.fn18

Authoritarian parenting tends to produce adults who may be narrowly successful, obedient, conformist (often with an undercurrent of resentment that can explode), and not particularly happy. Moreover, social skills are often poor because, instead of learning by experience, they grew up following orders.

permissive parenting, the aberration that supposedly let Boomers invent the 1960s. There are few demands or expectations, rules are rarely enforced, and children set the agenda. Adult outcome: self-indulgent individuals with poor impulse control, low frustration tolerance, plus poor social skills thanks to living consequence-free childhoods.

Why are peers so important? Peer interactions teach social competence—context-dependent behavior, when to be friend or foe, where you fit in hierarchies. Young organisms utilize the greatest teaching tool ever to acquire such information—play.

Play is vital. In order to play, animals forgo foraging, expend calories, make themselves distracted and conspicuous to predators. Young organisms squander energy on play during famines. A child deprived of or disinterested in play rarely has a socially fulfilling adult life.

some spices consumed by pregnant women get into amniotic fluid. Thus we may be born preferring foods our mothers ate during pregnancy—pretty unorthodox cultural transmission.59

A pregnant woman’s voice is audible in the womb, and newborns recognize and prefer the sound of their mother’s voice.

East Asians are more likely to invoke relational explanations built around the interactions of the ball with its environment—friction—while Westerners focus on intrinsic properties like weight and density. Westerners are more accurate at estimating length in absolute terms (“How long is that line?”) while East Asians are better with relational estimates (“How much longer is this line than that?”).

As in so many other species, our brains, particularly the neocortex and most particularly the frontal cortex, have coevolved with the social complexity of status differences. It takes a lot of brainpower to make sense of the subtleties of dominance relations.

Like so many other animals, we have an often-frantic need to conform, belong, and obey. Such conformity can be markedly maladaptive, as we forgo better solutions in the name of the foolishness of the crowd. When we discover we are out of step with everyone else, our amygdalae spasm with anxiety, our memories are revised, and our sensory-processing regions are even pressured to experience what is not true. All to fit in.

“Why did you never cheat? Is it because of your ability to see the long-term consequences of cheating becoming normalized, or your respect for the Golden Rule, or …?” The answer is “I don’t know [shrug]. I just don’t cheat.” This isn’t a deontological or a consequentialist moment. It’s virtue ethics sneaking in the back door in that moment—“I don’t cheat; that’s not who I am.” Doing the right thing is the easier thing.

Yes, you don’t act because someone else’s pain is so painful—that’s a scenario that begs you to flee instead. But the detachment that should be aimed for doesn’t represent choosing a “cognitive” approach to doing good over an “affective” one. The detachment isn’t slowly, laboriously thinking your way to acting compassionately as an ideal utilitarian solution—the danger here is the ease with which you can instead think your way to conveniently concluding this isn’t your problem to worry about. The key is neither a good (limbic) heart nor a frontal cortex that can reason you to the point of action. Instead it’s the case of things that have long since become implicit and automatic—being potty trained; riding a bike; telling the truth; helping someone in need.