Behave: The Biology of Humans at Our Best and Worst

by Robert M. Sapolsky

I think like an academic egghead, believing that if I write enough paragraphs about a scary subject, give enough lectures about it, it will give up and go away quietly. And if everyone took enough classes about the biology of violence and studied hard, we’d all be able to take a nap between the snoozing lion and lamb. Such is the delusional sense of efficacy of a professor.

Then there’s the other personal root for this book. I am by nature majorly pessimistic. Give me any topic and I’ll find a way in which things will fall apart. Or turn out wonderfully and somehow, because of that, be poignant and sad. It’s a pain in the butt, especially to people stuck around me. And when I had kids, I realized that I

umpteen

House two female rats together, and over the course of weeks they will synchronize their reproductive cycles so that they

wind up ovulating within a few hours of each other. Try the same with two human females (as reported in some but not all studies), and something similar occurs. It’s called the Wellesley effect, first shown with roommates at all-women’s Wellesley College.8

the things we do are unique. While a few other species have regular nonreproductive sex, we’re the only ones to talk afterward about how it was.

And the second example: In the mid-1960s, a rightist military coup overthrew the government of Indonesia, instituting the thirty-year dictatorship of Suharto known as the New Order.

aggression, violence, compassion, empathy, sympathy, competition, cooperation, altruism, envy, schadenfreude, spite, forgiveness, reconciliation, revenge, reciprocity, and (why not?) love. Flinging us into definitional quagmires.

Let’s examine this with respect to different types of “aggression.”

decrease the perpetrator’s stress hormone levels; giving ulcers can help you avoid getting them. And of course there is the ghastly world of aggression that is neither reactive nor instrumental but is done for pleasure.

For a neuroscientist it describes a consequence of a type of damage to the frontal cortex—in economic games of shifting strategies, individuals with such damage fail to switch to less altruistic play when being repeatedly

Elie Wiesel, the Nobel Peace Prize winner and concentration camp survivor: “The opposite of love is not hate; its opposite is indifference.” The biologies of strong love and strong hate are similar in many ways, as we’ll see.

instead of helping; turn on the PNS, and it’s the opposite. Given that the SNS and PNS do opposite things, the PNS is obviously going to be releasing a different neurotransmitter from its axon terminals—acetylcholine.* There is a second,

The same occurs transiently when you temporarily silence the amygdala by injecting Novocain into it.

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

The Amygdala as Part of Networks in the Brain Now that we know about the subparts of the amygdala, it’s informative to consider its extrinsic connections—i.e., what parts of the brain send projection to it, and what parts does it project to?25

“periaqueductal gray” (PAG);

projection from the “insular cortex,” an honorary part of the prefrontal cortex, which we will consider at length in later chapters.28 If you (or any other mammal) bite into rancid food,

This is a sprawling portfolio. I will group these varied functions under a single definition, pertinent to every page of this book: the frontal cortex makes you do the harder thing when it’s the right thing to do.

Frontal Metabolism and an Implicit Vulnerability

larger the PFC becomes—social complexity expands the frontal cortex.

We utilize the frontal cortex to do the harder thing in social contexts—we praise the hosts for the inedible dinner; refrain from hitting the infuriating coworker; don’t make sexual advances to someone, despite our fantasies; don’t belch loudly during the eulogy. A great way to appreciate the frontal cortex is to consider what happens when it is damaged.

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

The dlPFC is the decider of deciders, the most rational, cognitive, utilitarian, unsentimental part of the PFC. It’s the most recently evolved part of the PFC and the last part to fully mature.

mostly hears from and talks to other cortical regions. In contrast to the dlPFC, there’s the ventral part of the PFC, particularly the ventromedial PFC (vmPFC). This is the frontocortical region that the visionary neuroanatomist Nauta made an honorary member of the limbic system because of its interconnections with it. Logically, the vmPFC is all about the impact of emotion on decision making.

Similarly, humans with dlPFC damage are impaired in planning or gratification postponement, perseverate on strategies that offer immediate reward, and show poor executive control over their behavior.* Remarkably, the technique of transcranial magnetic stimulation can temporarily silence part of someone’s cortex, as was done in a

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.

Moreover, eventual decisions are highly utilitarian. vmPFC patients are atypically willing to sacrifice one person, including a family member, to save five strangers.62 They’re more interested in outcomes than in their underlying emotional motives, punishing someone who accidentally kills but not one who tried

to kill but failed, because, after all, no one died i...

It’s Mr. Spock, running on only the dlPFC. Now for a crucial point. People who dichotomize between thought and emotion often prefer the former, viewing emotion as suspect. It gums up decision making by getting sentimental, sings too loudly, dresses flamboyantly, has unsettling amounts of armpit hair. In...

* I recently found a startling example of unorthodox defining of terms. This concerned Menachem Begin, one of the surprising architects of the Camp David Peace Accords in 1978 as the prime minister of Israel. In the mid-1940s he headed the Irgun, the Zionist paramilitary group intent on driving Britain out of Palestine in order to facilitate the founding of Israel. The Irgun raised money to buy arms through extortion and robbery, hanged two captive British soldiers and booby-trapped their bodies, and carried out a series of bombings including, most notoriously, an attack on British headquarters at Jerusalem’s King David Hotel, an act that killed not only numerous British officials but also scores of Arab and Jewish civilians. And Begin’s account of these activities? “Historically we were not ‘terrorists.’

* This is termed “Pavlovian conditioning” in a nod to Ivan Pavlov; it’s the same process by which Pavlov’s dogs learned to associate the conditioned stimulus of a bell with the unconditioned stimulus of food, so that the former eventually was able to provoke salivation. Less reliable are “operant conditioning” approaches, in which the degree to which something is scary is assessed by how much an individual will work to avoid being exposed to it.