Behave: The Biology of Humans at Our Best and Worst

The brain is heavily influenced by genes. But from birth through young adulthood, the part of the human brain that most defines us (frontal cortex) is less a product of the genes with which you started life than of what life has thrown at you. Because it is the least constrained by genes and most sculpted by experience. This must be so, to be the supremely complex social species that we are. Ironically, it seems that the genetic program of human brain development has evolved to, as much as possible, free the frontal cortext from genes.

If we accept that there will always be sides, it’s a nontrivial to-do list item to always be on the side of angels. Distrust essentialism. Keep in mind that what seems like rationality is often just rationalization, playing catch-up with subterranean forces that we never suspect. Focus on the larger, shared goals. Practice perspective taking. Individuate, individuate, individuate. Recall the historical lessons of how often the truly malignant Thems keep themselves hidden and make third parties the fall guy. And in the meantime, give the right-of-way to people driving cars with the “Mean people suck” bumper sticker, and remind everyone that we’re all in it together against Lord Voldemort and the House Slytherin.

You don’t have to choose between being scientific and being compassionate.

Things that seem morally obvious and intuitive now weren’t necessarily so in the past; many started with nonconforming reasoning.

Why should people in one part of the globe have developed collectivist cultures, while others went individualist? The United States is the individualism poster child for at least two reasons. First there's immigration. Currently, 12 percent of Americans are immigrants, another 12 percent are children of immigrants, and everyone else except for the 0.9 percent pure Native Americans descend from people who emigrated within the last five hundred years. And who were the immigrants? Those in the settled world who were cranks, malcontents, restless, heretical, black sheep, hyperactive, hypomanic, misanthropic, itchy, unconventional, yearning to be rich, yearning to be out of their damn boring repressive little hamlet, yearning. Couple that with the second reason - for the majority of its colonial and independent history, America has had a moving frontier luring those whose extreme prickly optimism made merely booking passage to the New World insufficiently novel - and you've got America the individualistic. Why has East Asia provided textbook examples of collectivism? The key is how culture is shaped by the way people traditionally made a living, which in turn is shaped by ecology. And in East Asia it's all about rice. Rice, which was domesticated there roughly ten thousand years ago, requires massive amounts of communal work. Not just backbreaking planting and harvesting, which are done in rotation because the entire village is needed to harvest each family's rice. The United States was not without labor-intensive agriculture historically. But rather than solving that with collectivism, it solved it withe slavery.

In other words, the default state is to trust, and what the amygdala does is learn vigilance and distrust.

Testosterone also increases confidence and optimism, while decreasing fear and anxiety.5 This explains the “winner” effect in lab animals, where winning a fight increases an animal’s willingness to participate in, and its success in, another such interaction. Part of the increased success probably reflects the fact that winning stimulates testosterone secretion, which increases glucose delivery and metabolism in the animal’s muscles and makes his pheromones smell scarier. Moreover, winning increases the number of testosterone receptors in the bed nucleus of the stria terminalis (the way station through which the amygdala communicates with the rest of the brain), increasing its sensitivity to the hormone. Success in everything from athletics to chess to the stock

if you’re stressed like a normal mammal in an acute physical crisis, the stress response is lifesaving. But if instead you chronically activate the stress response for reasons of psychological stress, your health suffers. It

probably the most important fact about genetics and culture is the delayed maturation of the frontal cortex—the genetic programming for the young frontal cortex to be freer from genes than other brain regions, to be sculpted instead by environment, to sop up cultural norms. To hark back to a theme from the first pages of this book, it doesn’t take a particularly fancy brain to learn how to motorically, say, throw a punch. But it takes a fancy, environmentally malleable frontal cortex to learn culture-specific rules about when it’s okay to throw punches.

Sustained stress has numerous adverse effects. The amygdala becomes overactive and more coupled to pathways of habitual behavior; it is easier to learn fear and harder to unlearn it.

someone’s hand being poked with a needle, and subjects have an “isomorphic sensorimotor” response—hands tense in empathy. Among both whites and blacks, the response is blunted for other-race hands; the more the implicit racism, the more blunting. Similarly, among subjects of both races, there’s more activation of the (emotional) medial PFC when considering misfortune befalling a member of their own race than of another race.

If you (or any other mammal) bite into rancid food, the insular cortex lights up, causing you to spit it out, gag, feel nauseated, make a revolted facial expression—the insular cortex processes gustatory disgust. Ditto for disgusting smells.

Diallo, a West African immigrant in New York, matched a description of a rapist. Four white officers questioned him, and when the unarmed Diallo started to pull out his wallet, they decided it was a gun and fired forty-one shots. The underlying neurobiology concerns “event-related potentials” (ERPs), which are stimulus-induced changes in electrical activity of the brain (as assessed by EEG—electroencephalography). Threatening faces produce a distinctive change (called the P200 component) in the ERP waveform in under two hundred milliseconds. Among white subjects, viewing someone black evokes a stronger P200 waveform than viewing someone white, regardless of whether the person is armed. Then, a few milliseconds later, a second, inhibitory waveform (the N200 component) appears, originating from the frontal cortex—“Let’s think a sec about what we’re seeing before we shoot.” Viewing a black individual evokes less of an N200 waveform than does seeing someone white. The greater the P200/N200 ratio (i.e., the greater the ratio of I’m-feeling-threatened to Hold-on-a-sec), the greater the likelihood of shooting an unarmed black individual.

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.

As you study the trait in more environments, the heritability score will decrease. This is recognized by Bouchard: “These conclusions [derived from a behavior genetics study] can be generalized, of course only to new populations exposed to a range of environments similar to those studied.”31

All of that was eventually shown—there’s considerable adult neuro-genesis in the hippocampus (where roughly 3 percent of neurons are replaced each month) and lesser amounts in the cortex.22 It happens in humans throughout adult life. Hippocampal neurogenesis, for example, is enhanced by learning, exercise, estrogen, antidepressants, environmental enrichment, and brain injuryfn9 and inhibited by various stressors.fn10,23 Moreover, the new hippocampal neurons integrate into preexisting circuits, with the perky excitability of young neurons in the perinatal brain. Most important, new neurons are essential for integrating new information into preexisting schemas, something called “pattern separation.

Ultimately, forgiveness is usually about one thing—“This is for me, not for you.” Hatred is exhausting; forgiveness, or even just indifference, is freeing. To quote Booker T. Washington, “I shall allow no man to belittle my soul by making me hate him.” Belittle and distort and consume. Forgiveness seems to be at least somewhat good for your health—victims who show spontaneous forgiveness, or who have gone through forgiveness therapy (as opposed to “anger validation therapy”) show improvements in general health, cardiovascular function, and symptoms of depression, anxiety, and PTSD. Chapter 14 explored how compassion readily, perhaps inevitably, contains elements of self-interest. The compassionate granting of forgiveness epitomizes this.41

Success in everything from athletics to chess to the stock market boosts testosterone levels.

Consider this: the human genome codes for about 1,500 different TFs, contains 4,000,000 TF-binding sites, and the average cell uses about 200,000 such sites to generate its distinctive gene-expression profile.5 This is boggling.

The insula activates when we eat a cockroach or imagine doing so.

Someone does something lousy and selfish to you in a game, and the extent of insular and amygdaloid activation predicts how much outrage you feel and how much revenge you take.

How does this work? Rodents produce pheromonal odors with individual signatures, derived from genes called the major histocompatibility complex (MHC). This is a super variable gene cluster that produces unique proteins that form a signature for an individual. This was first studied by immunologists. What does the immune system do? It differentiates between you and invaders—“self” and “nonself”—and attacks the latter. All your cells carry your unique MHC-derived protein, and surveillance immune cells attack any cell lacking this protein password.

We love stress that is mild and transient and occurs in a benevolent context.

Despite these criticisms of his criticisms, my stance has a major problem, one that causes Morse to conclude that the contributions of neuroscience to the legal system “are modest at best and neuroscience poses no genuine, radical challenges to concepts of personhood, responsibility, and competence.”25 The problem can be summarized in a hypothetical exchange: Prosecutor: So, professor, you’ve told us about the extensive damage that the defendant sustained to his frontal cortex when he was a child. Has every person who has sustained such damage become a multiple murderer, like the defendant? Neuroscientist testifying for the defense: No. Prosecutor: Has every such person at least engaged in some sort of serious criminal behavior? Neuroscientist: No. Prosecutor: Can brain science explain why the same amount of damage produced murderous behavior in the defendant? Neuroscientist: No. The problem is that, even amid all these biological insights that allow us to be snitty about those silly homunculi, we still can’t predict much about behavior. Perhaps at the statistical level of groups, but not when it comes to individuals.

In a reductionist view, understanding something complex requires breaking it down into its components; understand those parts, add them together, and you’ll understand the big picture. And in this reductionist world, to understand cells, organs, bodies, and behavior, the best constituent part to study is genes.

Castration decreases sexual urges in the subset of sex offenders with intense, obsessive, and pathological urges. But otherwise castration doesn’t decrease recidivism rates; as stated in one meta-analysis, “hostile rapists and those who commit sex crimes motivated by power or anger are not amenable to treatment with [the antiandrogenic drugs].

The explains why basal levels of testosterone have little to do with subsequent aggression, and why increases in testosterone due to puberty, sexual stimulation, or the start of mating season don’t increase aggression either.

This system can indicate that this mouse is John Smith. How does it also tell that he’s your never-before-encountered brother? The closer the relative, the more similar their cluster of MHC genes and the more similar their olfactory signature. Olfactory neurons in a mouse contain receptors that respond most strongly to the mouse’s own MHC protein. Thus, if the receptor is maximally stimulated, it means the mouse is sniffing its armpit. If near maximally stimulated, it’s a close relative. Moderately, a distant relative. Not at all (though the MHC protein is being detected by other olfactory receptors), it’s a hippo’s

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 by-passing the cortex, but decreased accuracy. Thus the input shortcut may prompt you to see the cell phone as a gun. And the output shortcut may prompt you to pull a trigger before you consciously mean to.