Behave is a book by Robert Sapolsky about the biological underpinnings of human behavior.

The Triune Brain Model

A good way to understand how the human brain works is the Triune Brain Model, which divides the brain into 3 parts:

1) The Reptilian Brain (responsible for automatic functions like breathing)

2) The Emotional Brain (control emotions like anger or fear)

3) The Neocortex: Math, music, language, memory, and any abstract thinking. Other animals have it, but it is the largest in humans.

The amygdala plays a key role in phobias, aggression, anxieties, and flight/flight. Stress is when fight or flight is being triggered by the wrong things, and this can have deadly effects on health.

The frontal cortex makes you do the harder thing when it is the right thing to do — it is responsible for impulse control, strategic decisions, and long-term planning. It is the most recently evolved part of the brain.

Brain damage to the frontal cortex is associated with more aggressive behavior. The frontal cortex controls aggression, which is why the most common therapy for anger and anxiety is cognitive behavioral therapy, which teaches people to interpret the world differently — the rational frontal cortex retrains the amygdala.


We used to think that new neurons are created when we learn something, but this is not true. Neurons do not remember by forming new connections, but by strengthening existing connections. Neurons that fire together, wire together. That is why you will understand a book better if you read it twice.

Some neurons are always being formed through neurogenesis. 3 percent of the neurons in the hippocampus are replaced each month.

Teenagers get more upset than adults because of a lack of neocortical activity. If an adult feels socially excluded, they will initially feel disgust and anger, but then the ventrolateral neocortex activates, and quells those feelings. But a teenager does not experience as much prefrontal cortex activation, so they feel more hurt from rejection.


Yesterday’s unexpected pleasure is what we feel entitled to today, but what will not be enough tomorrow.

Dopamine release does not depend on how a happy a reward will make us feel. It depends on whether we are pursuing a reward that has a good chance of happening. That is what happened when monkeys pushed a lever that allowed them to eat raisins. But when the monkeys were rewarded only 50 percent of the time that they pushed the levers, their dopamine levels skyrocketed. That is why gambling is addictive.


Chronic stress, an unnatural distortion of the common animalistic fight or flight impulse, can be very damaging to our bodies and brains. Animals with lower social status usually have higher stress hormones.


One type of play that males do more than females is known as “rough and tumble” play. This type includes aggression, but not to cause harm. Puppies biting each other playfully, or kids wrestling, is practice for status competitions in the future.


What are genes? they are made of long strings of DNA. Our DNA is code written by different letters called nucleotides. This code is used to build proteins, which are the building blocks of our bodies. Half of your genetic blueprint is inherited from each parent.

Genes can increase the likelihood of depression, but only in people who have experienced childhood adversity. To know whether things are caused by genes or environment, scientists make comparisons between identical twins, adopted people, and identical twins adopted into different households.

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The genes that have survived were shaped by natural selection and sexual selection.

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