2689. Human Nature and Socialism, Part 3. Robert Sapolsky on Human Behavior

By Kamran Nayeri, June 7, 2026

Robert Sapolsky

Born in Brooklyn, New York, in 1957, Robert Morris Sapolsky is an American neuroscientist and primatologist. As John A. and Cynthia Fry Gunn Professor at Stanford University, he is a professor of biology, neurology, and neurosurgery. Sapolsky's research has focused on neuroendocrinology, particularly relating to stress. He is also a research associate with the National Museums of Kenya.

In what follows, I will outline Sapolsky’s grand synthesis of neuroscience, endocrinology, evolutionary biology, anthropology, and primatology as presented in his books Behave: The Biology of Humans at Our Best and Worst (2018) and Determined: A Science of Life Without Free Will (2023). His central argument is that no human behavior can be understood by looking at a single cause. Instead, every action is the outcome of a long causal chain extending from seconds before the act to millions of years of evolution.

Behave: Why humans do what they do

This 790-page book extensively discusses neurobiological foundations of human behavior, explaining how brain activity, particularly in the limbic and frontal cortex systems, dictates responses moments before an action is taken. It highlights the role of the triune brain model in processing everything from basic survival instincts to complex decision-making.

Sapolsky’s methodology is distinctive because it is neither purely neuroscientific nor purely sociological. Instead, Sapolsky develops what might be called a multi-level, historical-causal analysis of behavior.

His central methodological question is: What caused a particular behavior to occur at a particular moment?

To answer this, he works backward in time, examining layers of causation that extend from seconds before an action to millions of years before it.

The "Backward-in-Time" Method

Sapolsky begins with a specific behavior--for example, an act of aggression, altruism, cooperation, or prejudice—and asks what caused it. He then analyzes successively larger temporal scales:

First stage. One second before the behavior

What was happening in the brain?

• Neural circuits
• Amygdala activity
• Prefrontal cortex regulation
• Neurotransmitters

This is the immediate neurobiological explanation.

Second stage. Seconds to minutes before

What stimuli triggered the brain?

• Visual signals
• Sounds
• Social cues
• Threats or rewards

Behavior is seen as a response to environmental information processed by the nervous system.

Third stage. Hours to days before

What hormonal conditions existed?

• Cortisol
• Testosterone
• Oxytocin
• Dopamine

Hormones alter how the brain responds to stimuli.

Fourth stage. Months to years before

What developmental experiences shaped the individual?

• Childhood experiences
• Trauma
• Attachment
• Learning
• Socialization

The nervous system itself has been molded by prior experience.

Fifth stage. Genetic and epigenetic influences

What predispositions exist?

• Genes affecting temperament
• Gene-environment interactions
• Epigenetic modifications

Importantly, Sapolsky rejects genetic determinism. Genes influence probabilities, not fixed outcomes.

Sixth stage. Cultural influences

What social world shaped the person?

• Norms
• Institutions
• Religion
• Economic systems
• Political structures

Culture becomes a causal force in behavior.

Seventh stage. Evolutionary history

Why does our species possess these capacities at all?

• Evolution of cooperation
• Group identity
• Dominance hierarchies
• Empathy
• Aggression

Here Sapolsky draws on primatology, evolutionary biology, and anthropology.

Some conclusions

The following are some of the conclusions Sapolsky draws in Behave.

A. The nature-versus-nurture debate is largely obsolete

Sapolsky concludes that genes and environment are inseparable. Genes influence how organisms respond to environments, while environments influence how genes are expressed through developmental and epigenetic processes.

Thus, human behavior is always the product of gene-environment interaction.

B. The brain is highly plastic

Another major conclusion is that human brains are not fixed. Experience alters neural connections, emotional responses, cognitive capacities, stress systems, and even gene expression.

This means that neither virtue nor violence is permanently built into human beings.

C. Humans possess capacities for both extraordinary cruelty and extraordinary cooperation

Sapolsky rejects theories that portray humans as either naturally selfish or naturally good.

Humans have evolved capacities for aggression, domination, tribalism, and xenophobia,  but also, for empathy, cooperation, altruism, and reconciliation.

Both tendencies are deeply rooted in our biology.

D. Context matters enormously

A recurring conclusion throughout Behave is that behavior changes dramatically depending on circumstances.

People who behave compassionately in one context may behave cruelly in another.

Situational factors can often outweigh stable personality traits.

This insight draws partly from classic social psychology experiments and partly from neuroscience.

E. Tribalism is natural but not fixed

Sapolsky concludes that humans have evolved tendencies to divide the world into “us” and “them.” However, he emphasizes that group boundaries are remarkably flexible. People can rapidly redefine who belongs to "us." For Sapolsky, this flexibility provides grounds for optimism.

The same biological mechanisms that produce prejudice can also support broader forms of solidarity.

F. Social inequality has biological consequences

One of Sapolsky's longstanding research interests concerns stress and hierarchy. He concludes that chronic inequality, subordination, and insecurity produce measurable biological effects on health and behavior.

The social environment literally becomes embodied.This links social structures to biological outcomes.

G. Moral behavior depends heavily on social conditions

Sapolsky repeatedly argues that if societies wish to encourage cooperation, tolerance, and empathy it should create institutions and environments that support those behaviors. He is skeptical of explanations that focus solely on individual moral character. Instead, he emphasizes the importance of social arrangements.

H. Traditional notions of free will are deeply problematic

This conclusion becomes even more explicit in his later book, Determined, but its foundations are already present in Behave.

Sapolsky argues that every action arises from prior causes: genes, fetal development, childhood, culture, brain states, immediate circumstances.

As a result, he questions whether people could ever have acted independently of those causes. This does not mean behavior is random; rather, it is caused by factors beyond conscious control.

I. Understanding causation should increase compassion

This is perhaps the ethical conclusion that runs through the entire book. Sapolsky believes that understanding the causes of behavior should make us less self-righteous, less punitive, more empathetic. If behavior arises from biological and social histories that individuals did not choose, then moral judgment should be tempered by such understanding.

Determined: A Science of Life Without Free Will

In this 511-page book, Robert Sapolsky takes the argument implicit in Behave to its logical conclusion: human beings do not possess free will in the traditional sense.

However, the book is not merely a philosophical argument. Sapolsky attempts to synthesize findings from neuroscience, genetics, endocrinology, psychology, developmental biology, and social science to show that every human action arises from causes that precede conscious choice.

His central thesis can be summarized as follows: A person could not have acted differently from how they acted, because every factor that produced the action was itself caused by prior factors over which the person had no control.

Sapolsky asks what caused a decision at a particular moment. As in Behave, he works backward to find the causal chain for the decision. He argues that at no point do we encounter an independent "chooser" standing outside this causal chain. Instead, we find only more causes.

The core claim

Sapolsky rejects what philosophers often call libertarian free will—the idea that a person could have genuinely chosen otherwise under exactly the same conditions.

He argues that every thought emerges from brain activity. Brain activity arises from prior physical and biological causes. Those causes arise from earlier biological, environmental, social and historical causes. Therefore, no action is ultimately self-created.

The traditional image of autonomous self-making uncaused choices is, in his view, an illusion.

What about conscious choice? Sapolsky does not deny that people deliberate. We weigh alternatives, reflect, and make plans. However, he argues that the mechanisms that generate preferences, desires, values, motivations, and reasoning styles, were themselves produced by prior causes. Thus, while conscious deliberation is real, it is not evidence for free will. The deliberative process is itself part of the causal chain.

Sapolsky draws on several sources of evidence.

Neuroscience: Experiments often show measurable brain activity precedes conscious awareness of decisions. The brain appears to begin preparing actions before people report deciding.

Genetics and Development: Temperament, impulse control, risk-taking, and emotional regulation are influenced by genes, prenatal conditions, and childhood experiences.  Individuals do not choose these starting points.

Social Environment: Economic conditions, education, trauma, discrimination, and profoundly shape behavior. People inherit social circumstances rather than choosing them.

Some people argue that quantum indeterminacy or randomness creates freedom. Sapolsky rejects this. A random event is not a free choice. Randomness may undermine strict determinism, but it does not create an autonomous will.

Implications for morality

This is where Sapolsky becomes most controversial. He argues that if free will does not exist, then traditional notions of moral blameworthiness become difficult to defend. No one chooses their genes, their prenatal environment, or their childhood circumstances. If behavior emerges from factors beyond personal control, then punishment justified by retribution becomes questionable.

Sapolsky does not argue for abolishing laws, courts, or prisons. Instead, he proposes a more pragmatic approach. Society may need to restrain dangerous individuals, protect the public, and rehabilitate offenders, but should do so without the belief that offenders freely choose their character.

He often compares this to dealing with a dangerous disease. Society protects itself but without hatred or moral condemnation.

A major ethical conclusion of the book is that abandoning free will should increase compassion.

When we understand how behavior is shaped by biology, history, culture, and social conditions, we become less inclined toward self-righteousness and vengeance.

For Sapolsky, understanding causation should foster empathy.

Major Criticisms

The book has attracted much praise but also some criticism from philosophers and some scientists. Common objections include:

Philosophical view of free will: many philosophers do not believe free will requires an uncaused soul or independent self. Instead, they defend compatibilism, the belief that free will and determinism are mutually compatible and that it is possible to believe in both without being logically inconsistent even in a causally determined world.

Sapolsky largely rejects this position.

References:

Sapolsky, Robert. Behave: The Biology of Humans at Our Best and Worst. 2018. 

____________.  Determined: A Science of Life without Free Will. 2023.