[Book Notes] 10 insights: Behave

I first heard of Prof. Sapolsky in an MBA class on entrepreneurship. In the class, we were discussing the behavior traits of successful entrepreneurs (courage, risk taking, influence etc) and were trying to answer the question: How much of the behavior can be explained by biology vs. the actual choices by the entrepreneur. And if most of the entrepreneurial traits are determined by biology then should someone even aspire to be an entrepreneur if he/she does not have the requisite “biology”? To learn more about this topic, I picked up Prof. Sapolsky’s magnum opus, Behave, last year and I was not disappointed. The book talks about various factors that can influence human behavior: genes, hormones, brain regions, culture etc. My notes from the book are as follows:


Network of neurons are adept at transmitting signals and can achieve complicated circuitry to control memory, action and behavior

Neuron is the basic cell type of the nervous system. The inside of neuron is negatively charged when it is not activated and it is positively charged when the neuron is activated. The internal negative state is called the resting potential and the excited state is called the action potential.

A neuron ends in dendritic fibrils (at the head of neuron) and axon fibrils (at the tail of neuron). Excitation of a single dendritic fibril is not enough to pass the excitation down to the axonal end and on to the next neuron. In order to get sufficient excitation to sweep from the dendritic end of the neuron to the axonal end, you have to have summation i.e. the same spine must be stimulated repeatedly and/or, more commonly, multiple spinal neurons must be stimulated at once. At the base of the axon, where it emerges from the cell body, is a specialized part (called the axon “hillock”). If all those summated dendritic inputs produce enough of a ripple to move the resting potential around the hillock from -70 mV to around -40 mV, a threshold is passed.

From an informational standpoint, a neuron has two different types of signaling systems. From the dendritic spines to the starts of the axon hillock, it’s an analogue signal, with gradations of signals that dissipate over space and time. And from the axon hillock to the axon terminals, it’s a digital system with all-or-none signaling that regenerates down the length of the axon.

Structure of a neuron

Structure of a neuron

Any given neuron integrates the inputs from all the neurons projecting to it. The more neurons that Nneuron A projects to, the more neurons it can influence; however, the more neurons it projects to, the smaller its average influence will be at each of those target neurons. An average neuron has ~10,000 dendritic spines and about the same number of axon terminals. Factor in a hundred billion neurons, and you see why brains, rather than kidneys, write poetry.

A neuron also has a layer of insulation called a myelin sheath; this “myelination” causes the action potential to shoot down the axon faster. The threshold of the axon hillock can change over time i.e. the neuron’s excitability can change. Hormones, nutritional state, experience are some of the factors that can change the threshold.

There are micro-microscopic gaps between axon terminals and dendritic spines; these gaps are called “synapses”. Inside each axon terminal, tethered to the membrane, are little balloons called vesicles, filled with many copies of a chemical messenger. The action potential triggers the release of these chemical messengers into the synapse. The chemicals float across the synapse and reach and excite the dendritic spice of the neuron across the synapse. These chemical messengers are called neurotransmitters.

Neurotransmitters in a synapse

Neurotransmitters are the chemical messengers for transmitting signal from one neuron to the next.

The neurotransmitter molecule has a distinctive shape. The receptor has a binding pocket of a distinctive shape that is perfectly complementary to the shape of the neurotransmitter. Thus, the neurotransmitter fits into the receptor like a key into a lock.

The neurotransmitter does not bind to the receptors forever. Instead they float off the receptors, at which point the neurotransmitters have to be cleaned up. This occurs in one of two ways:

  1. There are “re-uptake pumps” in the membrane of the axon terminal. They take up the neurotransmitters and recycle them, putting them back into those secretory vesicles to be used again.

  2. The neurotransmitter can be degraded in the synapse by an enzyme, with the breakdown products flushed out to the extracellular environment

Therefore, the amount of neurotransmitter signaling across a synapse can be increased in various ways: (1) increase the amount of neurotransmitter released, (2) increase the amount of receptor in the dendritic spine of the receiving neuron, (3) decrease the activity of the re-uptake pumps or (4) decrease the activity of the degradative enzyme and, thus, reduce the amount of neurotransmitter that is removed from the synapse.

Some neurotransmitters have more excitatory effects than others and for different durations. Some neurotransmitters make the receiving neuron even more negative i.e. they have an inhibitory effect. Therefore, a neuron with its ten thousand dendritic spines is getting excitatory inputs of differing magnitudes from various neurons, getting inhibitory ones from other neurons, and integrating all of this at the axon hillock.

Changes in neurotransmitters can have a large impact on the human body. For e.g. Curare, the poison used in darts by Amazonian tribes, blocks acetylcholine receptors. Acetylcholine stimulates diaphragm to contract. Therefore, curare can stop breathing.

Network of neurons can achieve very complex circuitry. For e.g. in the circuit shown below, Neuron A stimulates neuron B (i.e. has a positive effect). Neuron A also stimulates neuron C. Neuron C sends an inhibitory projection back onto neuron A, forming a negative feedback loop. What better way to energetically communicate that it’s all over than to become majorly silent, thanks to the feedback loop? It’s a means of sharpening a signal over time. Moreover, neuron A can “determine” how powerful that negative feedback signal will be by how many of the ten thousand axon terminals it shunts toward neuron C instead of B.

Neuron circuit

Neuron circuit to sharpen a signal

[Note: The above information is contained in Appendix A of the book. This appendix is amongst the best overview of neurons and how signals are transmitted through the nervous system that I have read. For more details, I strongly encourage you to read the Appendix]



Greater release of dopamine is perceived as pleasure.

The dopamine system is about reward. Various pleasurable stimuli activates neurons, triggering their release of dopamine. Some evidence:

  1. Drugs like cocaine, heroin, alcohol releases dopamine 

  2. Chronic stress or pain depletes dopamine and decreases the sensitivity of dopamine neurons to stimulation, producing the defining symptom of depression – “anhedonia”, the inability to feel pleasure

  3. Some rewards such as sex releases dopamine in almost every specie. For humans, just thinking about sex also suffices

  4. Food evokes dopamine release in hungry individuals of all species

  5. Overbidding in auctions: This is interpreted as reflecting the additional award of besting someone in the competitive aspect of bidding. Thus, winning an auction is intrinsically socially competitive unlike winning a lottery. Winning a lottery and winning a bid both activated dopamine signaling in subjects; losing a lottery had no effect, while losing a bidding war inhibited dopamine release

  6. There is dopaminergic activation during schadenfreude – gloating over an envied person’s far from grace.



Dopamine is not just about reward anticipation; it fuels the goal-directed behavior needed to gain that reward

The pleasure (i.e. dopamine release) is in anticipation of reward and the reward itself is nearly an afterthought (unless of course the  reward fails to arrive). An analogy: If you know your appetite will be sated, pleasure is more about the appetite than about the sating.

Dopamine release in anticipation of reward

More dopamine is released even before the reward is received. Therefore, more pleasure is experienced in anticipation of the reward vs. getting the reward itself.

The magnitude of an anticipatory dopamine rise reflects two variables: (1) Size of the anticipated reward. Greater the anticipated reward, greater is the dopamine release and (2) If the anticipated reward does not come all the time then the magnitude is higher (completely unexpected). Nothing fuels dopamine release like the “maybe” of intermittent reinforcement. Anticipatory dopamine release peaks with the greatest uncertainty as to whether a reward will occur or not.

Dopamine release when the outcome is uncertain

There is additional dopamine released if there is uncertainty in the outcome.

This is used in Vegas. Gambling shouldn’t evoke much anticipatory dopamine given the astronomical odds against winning. But the behavioral engineering (24/7 activity, lack of time cues, cheap alcohol pickling brain judgement, manipulations to make you feel that today is your lucky day) distorts and shifts the perception of the odds into a range where dopamine pours out.

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. Therefore, dopamine is not about the happiness of reward. It is about the happiness of pursuit of reward that has a decent chance of occurring. For e.g. in some studies, the work required was prolonged and the reward was substantially delayed. In those scenarios, there is a secondary rise of dopamine, a gradual increase that fuels the sustained work.

Dopamine release when the reward is received after long time

Gradual dopamine increase (in cases where the reward is received after a long time) helps in continuous investment in the work

Humans delay gratification for very long times. We use the dopaminergic power of the happiness of pursuit to motivate us to work for rewards that come after we are dead – depending on your culture, this can be knowing that your nation is closer to winning a war because you have sacrificed yourself in battle, that your kids will inherit money because of your financial sacrifices, or that you will spend eternity in paradise.



Behavior is affected by subliminal cues.

Visual cues of cute baby-ness (big eyes, shortened muzzle, round forehead) drive mammals crazy and make them take care of the baby. This has been seen not just for human babies but for other animals too. For e.g. a significant factor in how much money people pledge to donate to help an endangered species is the relative size of the animal’s eyes. Stephen Jay Gould noted that Walt Disney understood the alterations that were needed to make rodents into Mickey Mouse.

People think that potato chips are better if they make a crunch noise. Juries view black (but not white) male defendants more favorably if they are wearing big, clunky glasses; some defense attorneys even exploit this “nerd defense” by accessorizing their clients with fake glasses. Attractive people are judged to be smarter, kinder and more honest. We are more likely to vote for them, hire them and less likely to convict them. The more expensive a supposed (placebo) painkiller, the more effective people report it to be. 

Most of subliminal information comes from the face. The shape of women’s face changes during their ovulatory cycle and men prefer female faces at the time of ovulation. Eyes give the most information. For e.g. take pictures of two faces with different emotions, and switch different facial parts between the two with cutting and pasting. Most people detect the emotion depicted via the eyes.

Behavior is also affected by language cues. For e.g calling a game as the “Wall Street game” makes people less cooperative vs. calling it a “community game”.

An unsettling sensory cue concerns race. Our brains are incredibly attuned to skin color and are able to note the color of the skin really fast. Amygdala of the person (center of fear, aggression) activates when he/she sees the face of a person that does not belong to the same race. People judge neutral other-race faces as angrier than neutral same-race faces.

In a study, it was found that threatening faces produce a distinctive change (called the P200 component) in the ERP waveform in under 200 milliseconds. A few seconds later, an inhibitory waveform (called the N200 component) appears. The ratio of P200/N200 determines our reaction to the threatening face – probability of a violent reaction is higher if the ratio is higher. Among white subjects, viewing someone black evokes a stronger P200 waveform than viewing someone white, regardless of whether the person is armed. Viewing a black face evokes less of a N200 waveform than does seeing someone white.



We love stress that is mild and transient and occurs in a benevolent context. We get sick from activating the stress response too often, too long and for purely psychological reasons.

The complete absence of stress is aversively boring. Moderate, transient stress is wonderful – various aspects of brain function are enhanced, glucocorticoids level in that range leads to dopamine release. Moderate stress is also needed in some scenarios – for e.g. when we are running for our lives. Sustained stress makes the sensory shortcut between thalamus and amygdala more active – leading to a tradeoff between speed and accuracy i.e. we will become more prone to act fast to stimulus vs. using judgement/logic to respond to it.

Glucocorticoids release and stress

Moderate release of glucocorticoids is preferred but sustained high levels lead to stress

Amygdala (center of fear, aggression) is highly sensitive to glucocorticoids. Amygdala has lots of glucocorticoids receptors and glucocorticoids increases the excitability of amygdala neurons, particularly in a region, which has a role in learning fear.

Stress fosters aggression because aggression reduces stress. Shock a rat and its glucocorticoids levels increases. Various things can buffer the rat during shocks: running on a running wheel, eating. But an effective mean is to bite another rat i.e. aggression. This is called stress induced displacement aggression. Humans are great at it. For e.g. higher spousal and child abuse during economic downturn, which is a time for more stress.

Stress also biases us towards selfishness. In one study, subjects answered questions about moral decision making scenarios after a social stressor. The more glucocorticoid levels rose, the more egoistic the answer. Glucocorticoids also narrow who counts as enough of an “Us” i.e. people who are stressed are more likely to act badly towards an outsider/Them.



Merely grouping people can activate parochial biases; Our feeling and response towards “Them” is determined by the level of warmth that we feel towards them and the competence that we attribute to them.

The amygdala activates when viewing fearful faces, but only of group members; when its an out-group member, showing fear might even be good news. In most animals, the insula is associated with gustatory disgust. However, in humans, the insula is also associated with moral and aesthetic disgust. Pictures of drug addicts or homeless people activates the insula. Thems are also frequently viewed as simpler and more homogenous than us, with simpler emotions and less sensitivity to pain. Thats how the antebellum South looked at slaves.

Our reaction to “Them” is determined by the level of warmth that we feel towards them and the level of competence that we attach to them. For e.g. we have low warmth for homeless people and believe that they have low competency. Therefore, we feel disgust for them. On the other hand, we have low warmth for immigrants but can attach high competency to them as they may be more educated. In such cases, we feel envious.

Feeling towards others/ them

Feeling towards Them is determined by the level of warmth and competence



Tit for Tat is one of the best strategies to use in repeated games.

Tit for Tat strategy – Cooperate in the first round. After that, you do whatever the other player did in the previous round.

Tit for Tat can never win. The best case is a draw, if playing against another person using Tit for Tat or someone using an “always cooperate” strategy. Every other strategy would always beat Tit for Tat by a small margin. However, other strategies playing against each other can produce catastrophic losses. And when everything is summed, Tit for Tat wins. It lost nearly every battle but won the war. 

A challenge with Tit for Tat is if signal error takes place then a pair of Tit for Tat players can get locked forever in a seesawing of defection. There are 2 solutions: (1) Contrite Tit for Tat retaliates only if the other side has defected twice in a row. (2) Forgiving Tit for Tat automatically forgives one third of defections. Both avoid doomsday signal-error scenarios but are vulnerable to exploitation. 

Another solution to signal error challenge is to use a shifting strategy. At the beginning, start with Tit for Tat but after multiple rounds move to forgiving Tit for Tat. What is this transition from hard-assed, punitive Tit for Tat to incorporating forgiveness? Establishing Trust. 

Another real world elaboration was to factor the cost of certain strategies. For e.g. with Tit for Tat, the costs of monitoring for and then punishing cheating – costly alarm systems, police salaries and jail construction. These are superfluous in a world of no signal errors and nothing for but Tit for Tat-ers, and Tit for Tat strategy can be replaced by the cheaper Always cooperate strategy.



Culture can explain some behavioral components. For e.g. Americans generally demonstrate individualism vs. East Asians, who demonstrate collectivism.

In a study of employees throughout the world working for the same MNC bank, what was the most important reason cited to help someone? Among Americans, it was that the person had previously helped them; for Chinese, it was that the person was higher ranking; in Spain, that they were a friend or acquaintance.

Americans are more likely than East Asians to remember times in which they influences someone; conversely, East Asians are more likely to remember times when someone influenced them. US is the individualism poster child. Immigration is one of the explanations. 12% of Americans are immigrants, another 12% are children of immigrants and everyone else except for the 0.9% Native Americans descend from people that emigrated over the last 500 years.

And who were the immigrants? Those in the settled world who were cranks, malcontents, restless, yearning to be free, yearning to be rich. In contrast, East Asia is collectivist. In East Asia, it is all about rice. Rice requires massive amount of communal work. Collective labor is needed to transfer the ecosystem and then to harvest the rice.

Pastoralist roots have been suggested to explain the Southern culture of honor. For e.g. in a study, southerners showed massive increases in levels of testosterone and glucocorticoids in response to an insult.

Reaction to insult

Southerners had a higher reaction to insult compared to northeners



Why have stratified cultures dominated the planet? Stratified cultures are ideally suited to being conquerors – they come with chain of command. In addition, in an unstable environment, stratified societies are better able to survive resource shortages by sequestering mortality in the lower classes.

Inequality also makes people unhealthy. Researchers looked at Socioeconomic status (SES)/health gradient and identified that the poorer you are the worse is your health. They also ruled out the following:

  1. The gradient isn’t due to poor health driving down people’s SES. Instead low SES, beginning in childhood, predicts subsequent poor health

  2. It is not that the poor have lousy health and everyone else is equally healthy. Instead, for every step down the SES ladder, starting from the top, the average health worsens

  3. The gradient isn’t due to less health care access for the poor

  4. Only about 1/3 of the gradient is explained by lower SES equaling more health risk factors (e.g. lead in your water, nearby toxic waste dump) and fewer protective factors (e.g. gym membership)

Research shows that it is not being poor that predicts poor health but “feeling poor” i.e. someone’s subjective SES. Also its not so much that poverty predicts poor health; its poverty amid plenty – income inequality – that credits poor health. Some possible reasons:

  1. When social capital decreases (thanks to income inequality), psychological stress increases

  2. Neo-materialist explanation: If you want to improve health for the average person in society, you spend money on public good like public transit, safer streets, cleaner water. But the more income inequality, the greater the financial distance between the wealthy and the average and, thus, the less direct benefit the wealthy feel from improving public goods. Instead they benefit more from dodging taxes and spending on their private good – chauffeur, gated community. They also have resources (lobbying) to prevent spending on public good. This “secession of the wealthy” promotes “private affluence and public squalor”. Meaning worse health for the have-nots.

A rat being shocked activates a stress response. But a rat that can bit the hell out of another rat and reduce its stress response. Similarly, when inequality fuels violence, it is mostly the poor preying on the poor. Another example is that of “air rage”. If a plane has a first-class section then there is a 4X increase in the odds of a coach passenger having air rage. And when air rage is boosted in coach by reminders of inequality, the result is not a crazed coach passenger sprinting into first class but the coach passenger being mean to the person sitting next to him in coach.

Agriculture has also led to inequality. Agriculture makes for surplus and thus almost inevitably to the unequal distribution of surplus, generating inequality.



Growing cultures has to invent mechanisms for norm enforcement among strangers. The larger the group, the greater the punishment for norm violations and the more cultural emphasis on equitable treatment of strangers. Larger groups also evolved “third party punishment” – rather than victim punishing perpetrators, punishment is meted out by objective third parties.

Why does religion arise? Because it makes in-groups more cooperative and viable. Because humans need personification and to see agency and causality when facing the unknown. Or maybe inventing deities is an emergent by-product of our social brains. Desert cultures are prone towards monotheistic religion; rain forest dwellers prefer polytheistic ones. Nomadic pastoralist’s deities tend to value war and valor in battle. Agriculturalists invent gods, who alter the weather