Behave: The Biology of Humans at Our Best and Worst

by Robert M. Sapolsky

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.

What happened one second before the behavior that caused it to occur? This puts us in the realm of neurobiology, of understanding the brain that commanded those muscles.

What crucial things happened in the second before that pro- or antisocial behavior occurred? Or, translated into neurobiology: What was going on with action potentials, neurotransmitters, and neural circuits in particular brain regions during that second?

The hypothalamus, a limbic structure, is the interface between layers 1 and 2, between core regulatory and emotional parts of the brain.

What was an unexpected pleasure yesterday is what we feel entitled to today, and what won’t be enough tomorrow.

Thus, dopamine is about invidious, rapidly habituating reward.

Collectively, there is little evidence that women tend toward aggression around their menses or that violent women are more likely to have committed their acts around their menses. Nevertheless, defense pleas of PMS-related “diminished responsibility” have been successful in courtrooms.

There is no evidence to support pms symptoms in women cause aggression.

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.

Remarkably, the fetal brain generates far more neurons than are found in the adult. Why? During late fetal development, there is a dramatic competition in much of the brain, with winning neurons being the ones that migrate to the correct location and maximize synaptic connections to other neurons. And neurons that don’t make the grade? They undergo “programmed cell death”—genes are activated that cause them to shrivel and die, their materials then recycled.

As shown experimentally, during risky decision making, adolescents activate the prefrontal cortex less than do adults; the less activity, the poorer the risk assessment.

Sensorimotor stage (birth to ~24 months). Thought concerns only what the child can directly sense and explore. During this stage, typically at around 8 months, children develop “object permanence,” understanding that even if they can’t see an object, it still exists—the infant can generate a mental image of something no longer there.*

Preoperational stage (~2 to 7 years). The child can maintain ideas about how the world works without explicit examples in front of him. Thoughts are increasingly symbolic; imaginary play abounds. However, reasoning is intuitive—no logic, no cause and effect. This is when kids can’t yet demonstrate “conservation of volume.” Identical beakers A and B are filled with equal amounts of water. Pour the contents of beaker B into beaker C, which is taller and thinner. Ask the child, “Which has more water, A or C?” Kids in the preoperational stage use incorrect folk intuition—the water line in C is higher than that in A; it must contain more water.

Concrete operational stage (7 to 12 years). Kids think logically, no longer falling for that different-shaped-beakers nonsense. However, generalizing logic from specific cases is iffy. As is abstract thinking—for example, proverbs are interpreted literally (“‘Bird...

Formal operational stage (adolescence onward). Approaching adult levels of abstraction, reasoning, and metacognition.

In the 1950s Lawrence Kohlberg, then a graduate student at the University of Chicago and later a professor at Harvard, began formulating his monumental stages of moral development.17 Kids would be presented with moral conundrums. For example: The only dose of the only drug that will save a poor woman from dying is prohibitively expensive. Should she steal it? Why? Kohlberg concluded that moral judgment is a cognitive process, built around increasingly complex reasoning as kids mature. He proposed his famed three stages of moral development, each with two subparts.

Level 1: Should I Eat the Cookie? Preconventional Reasoning

Stage 1. It depends. How likely am I to get punished? Being punished is unpleasant. Aggression typically peaks around ages two through four, after which kids are reined in by adults’ punishment (“Go sit in the corner”) and peers (i.e., being ostracized).

Stage 2. It depends. If I refrain, will I get rewarded? Bein...

Both stages are ego-oriented—obedience and self-interest (wha...

ages eight thro...

Concern arises when aggression, particularly if callous and remorseless, doesn’t wane around these ages—this predicts an increased risk of adult ...

Level 2: Should I Eat the Cookie? Conventional Reasoning Stage 3. It depends. Who will be deprived if I do? Do I like them? What would other people do? What will people think of me for eating the cookie? It’s nice to think of others; it’s good to be well regarded.

Stage 4. It depends. What’s the law? Are laws sacrosanct? What if everyone broke this law? It’s nice to have order. This is the judge who, considering predatory but legal lending practices by a bank, thinks, “I feel sorry for these victims . . . but I’m here to decide whether the bank broke a law . . . and it didn’t.”

Conventional moral reasoning is relational (about your interactions with others and their consequences); most adolesc...

Level 3: Should I Eat the Cookie? Postconvent...

Stage 5: It depends. What circumstances placed the cookie there? Who decided that I shouldn’t take it? Would I save a life by taking the cookie? It’s nice when clear rules are applied flexibly. Now the judge would think: “Yes, the bank’s actions were legal, but ultimately laws exist to protect the weak from the mighty, so signed contract or otherwise, that bank must be stopped.” Stage 6: It depends. Is my moral stance regarding this more vital than some law, a stance for which I’d...

Stage 6 is also egotistical, implicitly built on self-righteousness that trumps conventional petty bourgeois rule makers and bean counters, The Man, those sheep who just follow, etc. To quote Emerson, as is often done when considering the postconventional stage, “Every heroic act measures itself by its contempt of some external good.”

“small but not negligible.”24 Criticism #3: Recall that adoption studies assume that if a child is adopted soon after birth, she shares genes but no environment with her biological parents. But what about prenatal environmental effects? A newborn just spent nine months sharing the circulatory environment with Mom.

Roughly half your genes come from each parent, but prenatal environment comes from Mom. Thus, traits shared more with biological mothers than with fathers argue against a genetic influence.*

Repeat the mantra: don’t ask what a gene does; ask what it does in a particular context.

“Culture,” naturally, has been defined various ways. One influential definition comes from Edward Tylor, a distinguished nineteenth-century cultural anthropologist. For him culture is “that complex whole which includes knowledge, belief, art, morals, law, custom, and any other capabilities and habits acquired by man [sic] as a member of society.”4

attaining high rank is about sharp teeth and good fighting skills. But maintaining the high rank is about social intelligence and impulse control: knowing which provocations to ignore and which coalitions to form, understanding other individuals’ actions.

For every step down the SES ladder, health is worse.

The problem isn’t that poor people have less health-care access. The gradient occurs in countries with socialized medicine and universal health care and for diseases whose incidence is independent of health-care access.

Subjective SES predicts health at least as accurately as objective SES, meaning that it’s not about being poor. It’s about feeling poor. (b) Independent of absolute levels of income, the more income inequality in a community—meaning the more frequently the poor have their noses rubbed in their low status—the steeper the health gradient.

This is so common that in one study faces judged to look more competent won elections 68 percent of the time.

As probably the strongest factor, of candidates with identical political stances, people are more likely to vote for the better-looking one. Given the preponderance of male candidates and officeholders, this mostly translates into voting for masculine traits—tall, healthy-looking, symmetrical features, high forehead, prominent brow ridges, jutting jaw.

liberals are more motivated to push toward situational explanations.

This was the finding that when people are hungry, they become less generous in economic games. A real-world example of this is startling (see graph on previous page)—in a study of more than 1,100 judicial rulings, prisoners were granted parole at about a 60 percent rate when judges had recently eaten, and at essentially a 0 percent rate just before judges ate (note also the overall decline over the course of a tiring day).

Is it okay to criticize your group to outsiders? Rightists: no, that’s disloyal. Leftists: yes, if justified. Should you ever disobey a law? Rightists: no, that undermines authority. Leftists: of course, if it’s a bad law. Is it okay to burn the flag? Rightists: never, it’s sacred. Leftists: come on, it’s a piece of cloth.

The conservative dislike of ambiguity has been demonstrated in numerous apolitical contexts (e.g., responses to visual illusions, taste in entertainment) and is closely related to the differing feelings about novelty, which by definition evokes ambiguity and uncertainty.

The differing views of novelty certainly explain the liberal view that with correct reforms, our best days are ahead of us in a novel future, whereas conservatives view our best days as behind us, in familiar circumstances that should be returned to, to make things great again. Once again, these differences in psychological makeup play out in apolitical realms as well—liberals are more likely to own travel books than are conservatives.

Authoritarian conservatives, but not liberals, responded more rapidly to threatening words like “cancer,” “snake,” or “mugger” than to nonthreatening words (e.g., “telescope,” “tree,” “canteen”). Moreover, as compared with liberals, such conservatives are more likely to associate “arms” with “weapons” (rather than with “legs”), more likely to interpret ambiguous faces as threatening, and more easily conditioned to associate negative (but not positive) stimuli with neutral stimuli.

most intergroup conflicts on our planet ultimately are cultural disagreements about whose “right” is righter.

In contrast, when doing moral decision making during Us-versus-Them scenarios, keep intuitions as far away as possible. Instead, think, reason, and question; be deeply pragmatic and strategically utilitarian; take their perspective, try to think what they think, try to feel what they feel. Take a deep breath, and then do it all again.*

What should be the IQ cutoff for someone to be smart enough to be executed? The standard is an IQ of 70 or higher, and debate concerns whether it should be an average of 70 across multiple IQ tests, or if achieving that magic number even once qualifies you for being executed. This issue pertains to about 20 percent of people on death row.4

It’s less than two centuries since science first taught us that the frontal cortex has something to do with appropriate behavior.

Less than seventy years since we learned that schizophrenia is a biochemical disorder.

Perhaps fifty years since we learned that reading problems of a type that we now call dyslexia aren’t due to laziness but instead invol...

Twenty-five since we learned that epigenetics ...