Highlights and Notes on Behave: The Biology of Humans at Our Best and Worst by Sapolsky, Robert M.

the most context-savvy part of the brain, the prefrontal cortex.

to first-year medical students, the SNS mediates the “four Fs—fear, fight, flight, and sex.”

The fuzzy distinction between innate and learned fear maps nicely onto the amygdala’s structure.

basolateral amygdala (BLA),

the BLA that learns fear and then sends the news to the central amygdala.

“periaqueductal gray” (PAG);

bed nucleus of the stria terminalis (BNST).

locus coeruleus,

But autonomic feedback influences the intensity of what is felt.

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

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.

von Economo neurons (aka spindle neurons).

prefrontal cortex (PFC),

Just think how around age three, our frontal cortices learned a rule followed for the rest of our lives—don’t pee whenever you feel like it—and gained the means to enact that rule by increasing their influence over neurons regulating the bladder.

And then one day you realize that you’re five measures past the trill, it went fine, and you didn’t have to think about it. And that’s when doing the trill is transferred from the frontal cortex to more reflexive brain regions (e.g., the cerebellum).

Often the neurobiology of automaticity mediates doing the hardest moral acts, while the neurobiology of the frontal cortex mediates working hard on a term paper about the subject.

His remaining right frontal cortical tissue had taken on some of the functions lost in the injury. Such malleability of the brain is the focus of chapter

And there’s another nonpathological circumstance where the PFC silences, producing emotional tsunamis: during orgasm.

show him a picture of someone of another race for only a tenth of a second. This is too fast for him to be aware of what he saw. But thanks to that anatomical shortcut, the amygdala knows . . . and activates. In contrast, show the picture for a longer time. Again the amygdala activates, but then the cognitive dlPFC does as well,

is increasingly activated; the person feels increasingly distressed. What neurological disease is involved? None. This is a typical teenager.

Antecedent reappraisal is why placebos work.

cognitive behavioral therapy (CBT)—for the treatment of disorders of emotion regulation.

Dopamine is synthesized in multiple brain regions. One such region helps initiate movement; damage there produces Parkinson’s disease. Another regulates the release of a pituitary hormone. But the dopaminergic system that concerns us arises from an ancient, evolutionarily conserved region near the brain stem called the ventral tegmental area (henceforth the “tegmentum”).

brain region to be introduced in this chapter, the nucleus accumbens (henceforth the “accumbens”).

anhedonia,” the inability to feel pleasure.

The mesolimbic dopamine system also responds to pleasurable aesthetics.

Punishing norm violations is satisfying.

Thus there’s dopaminergic activation during schadenfreude—gloating over an envied person’s fall from grace.

In order to accommodate the pleasures of both mathematics and orgasms, the system must constantly rescale to accommodate the range of intensity offered by particular stimuli. The response to any reward must habituate with repetition, so that the system can respond over its full range to the next new thing.

following a reward, the dopamine system codes for discrepancy from expectation—get what you expected, and there’s a steady-state dribble of dopamine. Get more reward and/ or get it sooner than expected, and there’s a big burst; less and/ or later, a decrease. Some tegmental neurons respond to positive discrepancy from expectation, others to negative; appropriately,

Once, we had lives that, amid considerable privation, also offered numerous subtle, hard-won pleasures. And now we have drugs that cause spasms of pleasure and dopamine release a thousandfold higher than anything stimulated in our old drug-free world.

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. But dopamine is more interesting than that.

Dopamine is not just about reward anticipation; it fuels the goal-directed behavior needed to gain that reward; dopamine “binds” the value of a reward to the resulting work. It’s about the motivation arising from those dopaminergic projections to the PFC that is needed to do the harder thing (i.e., to work).

In other words, dopamine is not about the happiness of reward. It’s about the happiness of pursuit of reward that has a decent chance of occurring.*

Dopamine and the frontal cortex are in the thick of this phenomenon. Discounting curves—a value of ¼ Z instead of ½ Z—are coded in the accumbens, while dlPFC and vmPFC neurons code for time delay. 102

Collectively these studies show that our dopaminergic system, frontal cortex, amygdala, insula, and other members of the chorus code for differing aspects of reward magnitude, delay, and probability with varying degrees of accuracy, all influencing whether we manage to do the harder, more correct thing. 104

No gerbil works hard at school to get good SAT scores to get into a good college to get into a good grad school to get a good job to get into a good nursing home.

Importantly, while increasing serotonin signaling did not lessen impulsiveness in normal subjects, it did in subjects prone toward impulsivity, such as adolescents with conduct disorder. How does serotonin do this? Nearly all serotonin is synthesized in one brain region,*

was organized around three themes: the hub of fear, aggression, and arousal centered in the amygdala; the hub of reward, anticipation, and motivation of the dopaminergic system; and the hub of frontal cortical regulation and restraint of behavior.

good neuropsychologist can discern more of what’s happening to someone with subtle but pervasive memory problems than can a gazillion-dollar brain scanner.

mainly because I think that a term like “forgiveness,” and others related to criminal justice (e.g., “evil,” “soul,” “volition,” and “blame”), are incompatible with science and should be discarded.

Consider, for example, the fusiform face area.

it’s about recognizing examples of things from categories that are emotionally salient to each individual.

field of ethology, the science of interviewing an animal in its own language.

(“ Studying rat social behavior in a cage is like studying dolphin swimming behavior in a bathtub” is an ethology adage).

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amygdala. It’s the frontal cortex exerting executive control over the deeper, darker amygdaloid response.

prosopagnosia),

Remarkably, if mixed-race subjects are told they’ve been assigned to one of the two races for the study, they show less fusiform response to faces of the arbitrarily designated “other” race. 12

This is so depressing—are we hardwired to fear the face of someone of another race, to process their face less as a face, to feel less empathy? No. For starters, there’s tremendous individual variation—not everyone’s amygdala activates in response to an other-race face, and those exceptions are informative.

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amygdala activation increases if loud rap music—a genre typically associated more with African Americans than with whites—plays in the background. The opposite occurs when evoking negative white stereotypes with death metal music blaring.

our brains constantly receive “interoceptive” information about the body’s internal state.

As a repeating theme, pain does not cause aggression; it amplifies preexisting tendencies toward aggression. In other words, pain makes aggressive people more aggressive, while doing the opposite to unaggressive individuals.

“Male generosity as a mating signal.”

And testosterone is everyone’s usual suspect when it comes to the hormonal causes of aggression.

Thus, some male aggression is testosterone independent.*

the stria terminalis (the way station through which the amygdala communicates with the rest of the brain),

Testosterone makes people cocky, egocentric, and narcissistic. 6

Dopamine is needed for place-preference conditioning to occur, and testosterone increases activity in the ventral tegmentum, the source of those mesolimbic and mesocortical dopamine projections.

Testosterone did not create new social patterns of aggression; it exaggerated preexisting ones.

Testosterone makes us more willing to do what it takes to attain and maintain status. And the key point is what it takes. Engineer social circumstances right, and boosting testosterone levels during a challenge would make people compete like crazy to do the most acts of random kindness. In our world riddled with male violence, the problem isn’t that testosterone can increase levels of aggression. The problem is the frequency with which we reward aggression.

Oxytocin and vasopressin are chemically similar hormones;

Things became interesting with the discovery that those hypothalamic neurons that made oxytocin and vasopressin also sent projections throughout the brain, including the dopamine-related ventral tegmentum and nucleus accumbens, hippocampus, amygdala, and frontal cortex,

neuropeptides;

Spray oxytocin up a woman’s nose (a way to get the neuropeptide past the blood-brain barrier and into the brain), and she’ll find babies to look more appealing. Moreover, women

So a hormone that evolved for mother-infant bonding plays a role in this bizarre, unprecedented form of bonding between species.

stated caustically, oxytocin makes people irrational dupes; stated more angelically, oxytocin makes people turn the other cheek.

autism spectrum disorders (ASD) (strikingly, people with ASD show blunted fusiform responses to

As emphasized by De Dreu, perhaps oxytocin evolved to enhance social competence to make us better at identifying who is an Us.

Oxytocin, the luv hormone, makes us more prosocial to Us and worse to everyone else. That’s not generic prosociality. That’s ethnocentrism and xenophobia.

Is PMS/ PMDD a biological disease or a social construct?

This view even had room for a socioeconomic critique, with howlers like “PMS [is] a mode for the expression of women’s anger resulting from her oppressed position in American capitalist society.”* 62

predominate in different populations.

Thus stress facilitates learning fear associations but impairs learning fear extinction.

Stated most broadly, sustained stress impairs risk assessment. 76

Humans excel at stress-induced displacement aggression—consider how economic downturns increase rates of spousal and child abuse.

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.

https://en.m.wikipedia.org/wiki/N-Methyl-D-aspartic_acid

LTP—“ long-term potentiation.”

how LTP works, and the key is that when NMDA receptors finally activate and open their channels, it is calcium, rather than sodium, that flows in. This causes an array of changes; here are a few:

This is LTD—long-term “depression”—experience-dependent, long-term decreases in synaptic excitability (and, interestingly, the mechanisms underlying LTD are not merely the opposite of LTP). LTD is not the functional opposite of LTP either—rather than being the basis of generic forgetting, it sharpens a signal by erasing what’s extraneous.

Somehow LTP-induced changes in the receptor are transferred to the next generation of copies.

Combining these effects—more excitable synapses in the amygdala, fewer ones in the frontal cortex—helps explain stress-induced impulsivity and poor emotional regulation.

(the BNST—bed nucleus of the stria terminalis).

glucocorticoids because it’s terrified, dendrites atrophy in the hippocampus. However, if it secretes

This expansion probably involved axonal sprouting and the formation of new connections.

one renowned study showed enlargement of that part of the hippocampus in London taxi drivers.

Meanwhile, while adolescent males don’t have equivalent hormonal gyrations, it can’t help that their frontal cortex keeps getting hypoxic from the priapic blood flow to the crotch.

Novelty craving permeates adolescence; it is when we usually develop our stable tastes in music, food, and fashion, with openness to novelty declining thereafter.

Recall from chapter 2 how the ventral tegmentum is the source of the mesolimbic dopamine projection to the nucleus accumbens, and of the mesocortical dopamine projection to the frontal cortex. During adolescence, dopamine projection density and

And the small reward? Accumbens activity declined. In other words, adolescents experience bigger-than-expected rewards more positively than do adults and smaller-than-expected rewards as aversive.

As has been said, the greatest crime-fighting tool is a thirtieth birthday.

Ironically, it seems that the genetic program of human brain development has evolved to, as much as possible, free the frontal cortex from genes.

(downside: this is also when kids first negatively stereotype categories of people).

But before we get carried away with the generosity of youth, there is already in-group bias; if the other child is a stranger, there is less egalitarianism. 14

Woody Guthrie wrote in “Pretty Boy Floyd,” “I love a good man outside the law, just as much as I hate a bad man inside the law.”*

economist Steven Levitt of the University of Chicago—it was the legalization of abortions. The authors’ state-by-state analysis of the liberalization of abortion laws and the demographics

of the crime drop showed that when abortions become readily available in an area, rates of crime by young adults decline about twenty years later.

By age five, the lower a child’s socioeconomic status, on the average, the (a) higher the basal glucocorticoid levels and/ or the more reactive the glucocorticoid stress response, (b) the thinner the frontal cortex and the lower its metabolism, and (c) the poorer the frontal function concerning working memory, emotion regulation, impulse control, and executive decision making; moreover, to achieve equivalent frontal regulation, lower-SES kids must activate more frontal cortex than do higher-SES kids. In addition, childhood poverty impairs maturation of the corpus callosum, a bundle

early adversity produces an adult organism more vulnerable to drug and alcohol addiction. The pathway to this vulnerability is probably threefold: (a) effects on the developing

Chronic stress depletes the mesolimbic system of dopamine, generating anhedonia.*

Two caveats: (a) there is no evidence that catastrophically violent individuals (e.g., mass shooters) are that way because of childhood exposure to violent media; (b) exposure does not remotely guarantee increased aggression—instead, effects are strongest on kids already prone toward violence.

What explains such resilience?

Except for the amygdala. Which is enlarged. That pretty much says it all.

less effective at eliciting female-typical sexual behavior (i.e., a back-arching reflex called lordosis).

before the start of the stretch of DNA coding for that gene is a short stretch called a promoter*—the “on” switch. What turns the promoter switch on? Something called a transcription factor (TF) binds to the promoter. This causes the recruitment of enzymes that transcribe the gene into RNA.

accumbens, that target of mesolimbic dopamine projection.

the two separate stretches of coding DNA are called “exons,” separated by an “intron.” Many genes are broken into numerous exons (with, logically, one less intron than the number of exons). How do you produce a protein from an “exonic” gene?

Even flies evolved such that their neurons are freed from the strict genetic marching orders they inherit.

extroversion, agreeableness, conscientiousness, neuroticism, and openness to experience (known as the “Big Five” personality traits).

DZ twins are “dichorionic,” meaning that they have separate placentas. In contrast, 75 percent of MZ twins share one placenta (i.e., are “monochorionic”).*

Lots of work has examined the genes involved, most broadly showing that variants that produce lowered dopamine signaling (less dopamine in the synapse, fewer dopamine receptors, or lower responsiveness of these receptors) are associated with sensation seeking, risk taking, attentional problems, and extroversion. Such individuals have to seek experiences of greater intensity to compensate for the blunted dopamine signaling.

after dopamine binds to receptors, it floats off and must be removed from the synapse.

That still doesn’t tell us why for some people novelty seeking means frequently switching their openings in chess games, while for others it means looking for a new locale because it’s getting stale being a mercenary in the Congo. No gene or handful of genes that we are aware of will tell us much about that.

The hormone is not a protein (none of the steroid hormones are), meaning there isn’t a testosterone gene.

Even more appropriately, all behavioral traits are affected to some degree by genetic variability. 65 They have to be, given that they specify the structure of all the proteins pertinent to every neurotransmitter, hormone, receptor, etc. that there is.

Frans de Waal: “culture” is how we do and think about things, transmitted by nongenetic means.

a school kid in Romania, Bulgaria, or Ukraine, and you’re about ten times more likely to be chronically bullied than a kid in Sweden, Iceland, or Denmark (stay tuned for a closer look at this). 10

cultures.*

American individualism is about noncooperation, rather than nonconformity).

The Southern sense of honor in place is also seen in Robert E. Lee; he opposed Southern secession, even made some ambiguous statements that could be viewed as opposed to slavery.

Sticks and stones might break your bones, but names will cause you to break the offender’s bones.

rest of the South? Disproportionately herders from Scotland, Ireland, and northern England.

Or translated from social science–ese, marked inequality makes people crummier to one another.

more unequal are incomes in a society, the more pronounced will be the disadvantages to its better-off members from public expenditure, and the more resources will those members have [available to them] to mount effective political opposition” (e.g., lobbying). Evans notes how this “secession of the wealthy” promotes “private affluence and public squalor.” Meaning worse health for the have-nots. 39

Turns out there’s a substantial predictor of it: if the plane has a first-class section, there’s almost a fourfold increase in the odds of a coach passenger having air rage. Force coach passengers to walk through first class when boarding, and you more than double the chances further.

Nevertheless, some of the highest-density places on earth—Hong Kong, Singapore, and Tokyo—have miniscule rates of violence. High-density living is not synonymous with aggression in rats or humans.

Over the last fifty years El Niños have roughly doubled the likelihood of civil conflict, mostly by stoking the fires of preexisting conflicts.

“Mickey Mouse has supernatural powers, but no one worships or would fight—or kill—for him. Our social brains may help explain why children the world over are attracted to talking teacups, but religion is much more than

Agriculture makes for sedentary living, leading humans to do something that no primate with a concern for hygiene and public health would ever do, namely living in close proximity to their feces.

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.

Dobzhansky, “Nothing in biology makes sense except in the light of evolution.” Including this book.

pleiotropy,”

example, primates’ prostates have high metabolic rates, enhancing sperm motility. Upside: enhanced fertility; downside: increased risk of prostate cancer.

major histocompatibility complex (MHC).

In the 1940s “game theory” was founded by the polymath John von Neumann, one of the fathers of computer science. Game theory is the study of strategic decision making. Framed slightly differently, it’s the mathematical study of when to cooperate and when to cheat.

there are frequently pairs where one human does all the labor, the other doing nothing other than intermittently handing him some green pieces of paper. The point is that animals have systems of reciprocity with sensitivity to cheating.

Tournament species, where males have minimal investment in a female’s future reproductive success, have numerous imprinted genes, while pair-bonders don’t. 42 What about humans? Stay tuned.

more radical view, held by Dawkins, is that the most appropriate level is that of individual genes—i.e., selfish genes, rather than selfish genomes.

The economist Samuel Bowles, of the Santa Fe Institute, emphasizes how intergroup conflict like war is the driving force for intragroup cooperation (“ parochial altruism”); he refers to intergroup conflict as “altruism’s midwife.” 46

called pseudospeciation, and as will be seen in chapter 15, it underpins many of our worst moments.

five thousand people from thirty-two hunter-gatherer societies from around the world* showed that only around 40 percent of people within bands are blood relatives. 63 In other words, hunter-gatherer cooperativeness, the social building block of 99 percent of hominin history, rests at least as much on reciprocal altruism among nonrelatives as on kin selection

three major criticisms of sociobiology.

phyletic gradualism”).

Instead there were long periods of stasis, of unchanged fossils, and then, in a paleontological blink of an eye, there’d be a rapid transition to a very different form. Maybe

As we saw in chapter 8, recent decades have provided many possible molecular mechanisms for rapid change. This is the world of macromutations: (a) traditional point, insertion, and deletion mutations in genes whose proteins have amplifying network effects (transcription factors, splicing enzymes, transposes) in an exon expressed in

Lactase persistence evolved and spread in a fraction of a geologic blink of an eye—in the last ten thousand years or so, coevolving with domestication of dairy animals.

The first generations with Westernized diets develop catastrophically high rates of obesity, hypertension, adult-onset diabetes, and death at early ages, thanks to “thrifty” genotypes that are great at storing nutrients, honed by millennia of sparser diets. But within a few generations diabetes rates begin to subside, as there is an increased prevalence in the population of “sloppier” metabolic genotypes. 70

And no matter how rapid the changes, there’s always some degree of gradualism—no female has ever given birth to a member of a new species. 72

“spandrels”

In that view, male nipples are spandrels—they serve an adaptive role in females and came along for the ride as baggage in

contrast, saying, “Sociobiologists imply that when an unfair feature of life is the case, it is because it ought to be.” And the sociobiologists responded by flipping is/ ought around: “We agree that life ought to be fair, but nonetheless, this is reality. Saying that we advocate something just because we report it is like saying oncologists advocate cancer.”

was a bold assertion that the heuristic of dialectical materialism not only extends beyond the economic world into the naturalistic one, but is ontologically rooted in the essential sameness of both worlds’ dynamic of resolution of irresolvable contradictions.* It is Marx and Engels as trilobite and snail.*

discussed in chapter 3, fifty-millisecond exposure to the face of someone of another race activates the amygdala, while failing to activate the fusiform face area as much as same-race faces do—all within a few hundred milliseconds.

The brain’s fault lines dividing Us from Them were shown in chapter 4’ s discussion of oxytocin. Recall how the hormone prompts trust, generosity, and cooperation toward Us but crappier behavior toward Them—

Humans committed themselves to a unique trajectory when we invented socioeconomic status. In terms of its caustic, scarring impact on minds and

bodies, nothing in the history of animals being crappy to one another about status differences comes within light-years of our invention of poverty.

The Kohlbergian emergence of increasingly complex stages of moral development is built on the Piagetian emergence of increasingly complex logical operations. They are similar, neurobiologically.

People with obsessive-compulsive disorder get mired in both everyday decision making and moral decision making, and their dlPFCs go wild with activity for both.

“Our moral brains evolved to help us spread our genes, not to maximize our collective happiness.”

by Gregory Hickok of the University of California at Irvine,

Dalai Lama, who is famously intrigued by neuroscience and who has said that if his Dalai Lama gig hadn’t come up, he would have wanted to be a scientist or engineer. The most publicized work revolves around the neuroimaging of Matthieu Ricard, a French-born Buddhist monk (who is the Dalai Lama’s French translator and who just happens to have a PhD in molecular biology from the Pasteur Institute—this is one interesting guy). 50

In response to the latter idea, the pages of this book show how our social world is ultimately as much a product of our determined, materialist brains as are our simple motor movements.* 15

Turns out that the same APA had filed a brief some years earlier in a different case, emphasizing that adolescents are sufficiently mature that they should be able to choose whether to have an abortion, even without parental consent.

And yes, being a child molester is as much a product of biology as is being a pedophile. To think otherwise is little more than folk psychology.

“Brains don’t kill people. People kill people.”

it.” 23

example, transcranial magnetic stimulation techniques that transiently activate or inactivate a part of the cortex can change someone’s moral decision making, decisions about punishment, or levels of generosity and empathy. That’s causality.

The biology of the behaviors that interest us is, in all cases, multifactorial—that is the thesis of this book.

This is a deep, atavistic pleasure. Put people in brain scanners, give them scenarios of norm violations. Decision making about culpability for the violation correlates with activity in the cognitive dlPFC. But decision making about appropriate punishment activates the emotional vmPFC, along with the amygdala and insula; the more activation, the more punishment.

But there is simply no place for the idea that punishment is a virtue. Our dopaminergic pathways will have to find their stimulation elsewhere.

zygomatic arches.

As we saw, small-band cultures (such as hunter-gatherers) rarely invent moralizing deities. It is not until cultures are large enough that people regularly interact anonymously with strangers that it becomes commonplace to invent a judgmental god—the Judeo-Christian/ Muslim deity.

Priming people to think of God as punitive decreases cheating; thinking of God as forgiving increases it.

“people killing each other over who has the better imaginary friend,”

It’s not religiosity that stokes intergroup hostility; it’s being surrounded by coreligionists who affirm parochial identity, commitment, and shared loves and hatreds.

inter-group

intergroup

Prisoner’s Dilemma shows that whoever takes the first cooperative step becomes one step behind.

It’s open-ended play that fosters cooperation—an unknown number of rounds, producing the shadow of the future, where retribution is possible and the advantages of sustained mutual

Sometimes it takes a village to ransack a neighboring village.

We’re the only species that institutionalizes reconciliation and that grapples with “truth,” “apology,” “forgiveness,” “reparations,” “amnesty,” and “forgetting.”

Thus TRCs show the differences between reconciliation and the likes of remorse and forgiveness.*

Irrational optimism can be great; it’s why only about 15 percent instead of 99 percent of humans get clinically depressed.

“humans are bad at [close-range, hand-to-hand] violence, even if civilization makes us a bit better at it.” 43

book On Killing: The Psychological Cost of Learning to Kill in War and Society, by David Grossman,

Of the almost 27,000 single-load muskets recovered from the field, almost 24,000 of them were loaded and unfired; 12,000 were loaded multiple times, 6,000 loaded three to ten times. Lots of soldiers were standing there thinking, “I’m going to shoot soon, yes I am,

humans show a strong natural aversion to killing at close range. The most resistance is against hand-to-hand combat with a knife or bayonet. Next comes short-range firing with a pistol, then long-range firing, all the way to the easiest, which is bombs and artillery.

But consider drone pilots—soldiers who sit in control rooms in the United States, directing drones on the other side of the planet. They are not in danger. Yet their rates of PTSD are just as high as those of soldiers actually “in” war.

It took him a long time to die. I just watched him. I watched him become the same color as the ground he was lying on.

45

It’s remarkable the things humans can spend their lives studying. You can be a coniologist or a caliologist, studying dust or birds’ nests, respectively. There are batologists and brontologists, pondering brambles and thunder, and vexillologists and zygologists, with their dazzling knowledge of flags and of methods for fastening things. On and on—odontology and odonatology, phenology and phonology, parapsychology and parasitology. A rhinologist and a nosologist fall in love and have a child who becomes a rhinological nosologist, studying the classification of nose diseases.

Like another widely dispersed primate, humans, baboons eat almost anything—fruit, plants, tubers, insects, eggs, prey they’ve killed, dead things they’ve scavenged.

discarded roast beef and drumsticks and plum pudding, and then waddle out for a nap. I’d even darted Garbage Dump animals and studied them with colleagues—they put on weight, thickened with subcutaneous fat, had elevated circulating levels of insulin and triglycerides, had the start of metabolic syndrome. 46

They stayed close together, sat in contact, and groomed more than average. Levels of aggression were lower, and in an informative way. Males still had a dominance hierarchy; number three would still fight with numbers four and two, defending his status and seeking a promotion. But there was minimal displacement aggression onto innocent bystanders—when number three lost a fight, he’d rarely terrorize number ten or a female. Stress hormone levels were low; the neurochemistry of anxiety and benzodiazepines worked differently in these individuals.

Adolescence shows us that the most interesting part of the brain evolved to be shaped minimally by genes and maximally by experience; that’s how we learn—context, context, context.

What I’ve just outlined is that a single dendritic fibril receives an excitatory signal from the previous neuron (i.e., the previous neuron has had an action potential); this generates an action potential in that dendrite, which propagates toward the cell body, over it, on to the axon, to the axon terminals, and signals the next neuron in line. Not true. Instead: So the neuron is sitting there with nothing to say, which is to say that it’s displaying a resting potential; all of its insides are negatively charged. Along comes an excitatory signal at that one dendritic fibril, emanating from the previous neuron in line. As a result, channels open and ions flow in and out of that one dendrite. But only a little bit. Not enough to make the entire inside of the neuron positively charged, simply a little less negatively charged just inside that dendrite (just to attach some numbers here that don’t matter in the slightest, the resting potential charge shifts from around–70 millivolts

two different types of signaling

analogue

digital

The brain is wired in networks of divergent and convergent signaling.

the axon terminals of one neuron don’t actually touch the dendritic spines of the next. Instead there’s a tiny gap between the two. This notion was called the “neuron doctrine.”

saw, some of the most interesting findings that help explain individual differences in the behaviors that concern us in this book relate to amounts of neurotransmitter made and released, and the amounts and functioning of the receptors, reuptake pumps, and degradative enzymes.

inhibitory neurotransmitters.

Neurotransmitters are therefore made from precursors that are plentiful; often they are simple dietary constituents. Serotonin and dopamine, for example, are made from the dietary amino acids tryptophan and tyrosine, respectively. Acetylcholine is made from dietary choline and lecithin.

tyrosine into dopamine.

two categories: those that increase signaling across a particular type of synapse, and those that decrease it.

“SSRI”—a selective serotonin reuptake inhibitor.

“feed-

forward inhibition.”

system down for a while. And that is precisely what we often do in such circumstances. An insect bite throbs unbearably, we scratch hard right around it to dull the pain, and the slow, chronic pain pathway is shut down for up to a few minutes.

So it’s important to distinguish between “neuronal nuclei” and “fibers of passage.”

Once secreted, it enters the bloodstream, where it can influence any cells throughout the body that possess receptors for it.*

In other words, a more manageable length. That RNA is then shipped to wherever it is supposed to be in the cell, where it then directs which amino acids are strung together in which sequence to form a protein (and there are amino acids floating around in a cell, ready to be grabbed for the protein-construction project). Think of RNA as a photocopy of a single page out of this vast twenty-thousand-page-long DNA encyclopedia.

there are three types of mutations that can occur. The first is called a point mutation. One single nucleotide is copied incorrectly.

Trouble. The next type of classical mutation is called a deletion mutation.

Finally, there are insertion mutations. During copying of the DNA to pass on to the next generation, a nucleotide is inadvertently copied twice, duplicated.

For reviews

V. Salimpoor et al., “Interactions Between the Nucleus Accumbens and Auditory Cortices Predicts Music Reward Value,” Sci 340 (2013): 216; G. Berns and S. Moore, “A Neural Predictor of Cultural Popularity,” J Consumer Psych 22 (2012): 154; S. Erk et al., “Cultural Objects Modulate Reward Circuitry,” Neuroreport 13 (2002): 2499.

This fact prompted Greene, in a conversation with me, to dryly note how Harvard’s budget projections incorporate the expectation that if they work hard enough, approximately 50 percent of junior faculty will receive tenure.

They are just plain “WEIRD”—Westernized, educated, industrialized, rich, and democratic.

* Related to this was the notion that most of the evolution of behavior was not about dealing with the social complexities of fellow species members but about dealing with abiotic (i.e., nonbiological) pressures. In other words, that behavior evolved mostly for dealing with the environment, rather than for competing with other individuals. Again, the main implication of that for our purposes is that it would be another way in which the gradualist importance of interindividual competition was less than the sociobiologists thought. This emphasis on the importance of abiotic selective pressures was common among Soviet evolutionary biologists, probably reflecting not only the Marxist ideology but also the awful winters.