Behave

Robert M. Sapolsky

First annotation on Apr 17th, 2023. Last on Mar 10th, 2025.

15 quotes

5

We activate the classical physiology of vigilance while watching a scary movie. We activate a stress response when thinking about mortality. We secrete hormones related to nurturing and social bonding, but in response to an adorable baby panda. And this certainly applies to aggression—we use the same muscles as does a male chimp attacking a sexual competitor, but we use them to harm someone because of their ideology.

6

Here are some words of central importance to this book: 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." Animal behaviorists dichotomize between offensive and defensive aggression, distinguishing between, say, the intruder and the resident of a territory; the biology underlying these two versions differs. Such scientists also distinguish between conspecific aggression (between members of the same species) and fighting off a predator. Meanwhile, criminologists distinguish between impulsive and premeditated aggression. Anthropologists care about differing levels of organization underlying aggression, distinguishing among warfare, clan vendettas, and homicide.
This plays out in a fascinating realm, as reported in Larissa MacFarquhar's 2009 New Yorker piece "The Kindest Cut." It concerns people who donate organs not to family members or close friends but to strangers. An act of seemingly pure altruism. But these Samaritans unnerve everyone, sowing suspicion and skepticism. Is she expecting to get paid secretly for her kidney? Is she that desperate for attention? Will she work her way into the recipient's life and do a Fatal Attraction? What's her deal? The piece suggests that these profound acts of goodness unnerve because of their detached, affectless nature.
Hot-blooded badness, warmhearted goodness, and the unnerving incongruity of the cold-blooded versions raise a key point, encapsulated in a quote of Freud's emphasized by Elie Wiesel, the Nobel Peace Prize winner and concentration camp survivor: "The opposite of love is not hate; its opposite is indifference."

7

Layer 1: An ancient part of the brain, at its base, found in species from humans to geckos. This layer mediates automatic, regulatory functions. If body temperature drops, this brain region senses it and commands muscles to shiver. If blood glucose levels plummet, that's sensed here, generating hunger. If an injury occurs, a different loop initiates a stress response
Layer 2: A more recently evolved region that has expanded in mammals. MacLean conceptualized this layer as being about emotions, somewhat of a mammalian invention. If you see something gruesome and terrifying, this layer sends commands down to ancient layer 1, making you shiver with emotion. If you're feeling sadly unloved, regions here prompt layer 1 to generate a craving for comfort food. If you're a rodent and smell a cat, neurons here cause layer 1 to initiate a stress response.
Layer 3: The recently evolved layer of neocortex sitting on the upper surface of the brain. Proportionately, primates devote more of their brain to this layer than do other species. Cognition, memory storage, sensory processing, abstractions, philosophy, navel contemplation. Read a scary passage of a book, and layer 3 signals layer 2 to make you feel frightened, prompting layer 1 to initiate shivering. See an ad for Oreos and feel a craving—layer 3 influences layers 2 and 1. Contemplate the fact that loved ones won't live forever, or kids in refugee camps, or how the Na'vis' home tree was destroyed by those jerk humans in Avatar (despite the fact that, wait, Na'vi aren't real!), and layer 3 pulls layers 2 and 1 into the picture, and you feel sad and have the same sort of stress response that you'd have if you were fleeing a lion.
The biggest disadvantage is how simplistic this is. For example: Anatomically there is considerable overlap among the three layers (for example, one part of the cortex can best be thought of as part of layer 2; stay tuned). The flow of information and commands is not just top down, from layer 3 to 2 to 1. A weird, great example explored in chapter 15: if someone is holding a cold drink (temperature is processed in layer 1), they're more likely to judge someone they meet as having a cold personality (layer 3). Automatic aspects of behavior (simplistically, the purview of layer 1), emotion (layer 2), and thought (layer 3) are not separable. The triune model leads one, erroneously, to think that evolution in effect slapped on each new layer without any changes occurring in the one(s) already there.
Limbic function is now recognized as central to the emotions that fuel our best and worst behaviors, and extensive research has uncovered the functions of its structures (e.g., the amygdala, hippocampus, septum, habenula, and mammillary bodies).
In another study subjects waited an unknown length of time to receive a shock. This lack of predictability and control was so aversive that many chose to receive a stronger shock immediately. And in the others the period of anticipatory dread increasingly activated the amygdala. Thus the human amygdala preferentially responds to fear-evoking stimuli, even stimuli so fleeting as to be below conscious detection.
In the very front is the prefrontal cortex (PFC), the newest part of the frontal cortex. As noted, the frontal cortex is central to executive function. To quote George W. Bush, within the frontal cortex, it's the PFC that is "the decider." Most broadly, the PFC chooses between conflicting options—Coke or Pepsi; blurting out what you really think or restraining yourself; pulling the trigger or not. And often the conflict being resolved is between a decision heavily driven by cognition and one driven by emotions.

Introduction

The sympathetic nervous system (SNS) mediates the body's response to arousing circumstances, for example, producing the famed "fight or flight" stress response. To use the feeble joke told to first-year medical students, the SNS mediates the "four Fs—fear, fight, flight, and sex." Particular midbrain/brain-stem nuclei send long SNS projections down the spine and on to outposts throughout the body, where the axon terminals release the neurotransmitter norepinephrine. There's one exception that makes the SNS more familiar. In the adrenal gland, instead of norepinephrine (aka noradrenaline) being released, it's epinephrine (aka the famous adrenaline).*
Meanwhile, the parasympathetic nervous system (PNS) arises from different midbrain/brain-stem nuclei that project down the spine to the body. In contrast to the SNS and the four Fs, the PNS is about calm, vegetative states. The SNS speeds up the heart; the PNS slows it down. The PNS promotes digestion; the SNS inhibits it (which makes sense—if you're running for your life, avoiding being someone's lunch, don't waste energy digesting breakfast).*
Where do these "Ohhh, the tone isn't scary anymore" neurons get inputs from? The frontal cortex. When we stop fearing something, it isn't because some amygdaloid neurons have lost their excitability. We don't passively forget that something is scary. We actively learn that it isn't anymore.*