by Negussie Tilahun, Ph.D.
May 2026
Sapolsky’s Determined is about human behavior, more precisely it is about the biology of human
behavior. The book challenges one of the strongest beliefs human beings hold about themselves:
the belief that we freely choose our actions. Sapolsky argues that free will does not exist because
every action we take is caused by something that came before it, and the chain continues
indefinitely. In his view, human behavior is part of an unbroken chain of biological and other
factors. This is not a simple casual argument. Throughout the book Sapolsky repeatedly argues
that behavior cannot be explained by isolating one factor. Human behavior emerges from the
interaction of biology, environment, experience, culture, and history. Genes function within
environments; neurons operate within networks of neurons; culture shapes biology while biology
simultaneously responds to culture. Thus, behavior is layered, interconnected, and accumulated
over time. The central points of the book is that human behavior is too complex to be reduced to
one variable or one cause.
One of the strengths of Determined is the way Sapolsky develops his argument. He gradually
builds it step by step using neuroscience, genetics, psychology, evolution, and philosophy. He
moves carefully from one level of explanation to another, connecting them into a broader
framework of human behavior. Whether one agrees with him or not, the result is a book that is
insightful and intellectually challenging.
The first part of the book discusses theories that are applied to explain free will. Sapolsky
discusses reductionism, chaos theory, emergence, and quantum indeterminacy. Reductionism
dominated the scientific community for a greater part of the 20th century. It analyzes problems
by reducing them to smaller parts. Sapolsky argues such methodologies face serious
shortcomings in analyzing complex systems like human behavior which cannot always be
understood in a linear way. His discussion of chaos theory is interesting. Chaos is not
understood in an ordinary way to mean disorder. In nonlinear systems, small changes at an initial
state can produce greater outcomes while major initial changes bring about minor or negligible outcomes. This is what we call unpredictability. Furthermore, some events are not caused by any
event preceding it. Understanding the starting state and the reproduction rule, “gives you the
means to describe complexity but not the means to describe it” (p. 157). Also, some unique now
are created by a unique or multiple just unique before. This is the explanation given to what we
experience when we are suddenly and without any apparent reason change our course of action.
Sapolsky argues that unpredictability does not imply freedom. One of the important points that
he makes in his book is that a system can be unpredictable while it is fully determined by prior
factors.
Sapolsky is equally skeptical of attempts to rescue free will through quantum mechanics. In the
hidden world of quantum, particles vanish and reappear, forces act without contact and certainty
dissolve into chance. Some thinkers have argued that this indeterminacy may open the door to
explaining free will. Sapolsky rejects this conclusion. He argues that people who propose these
points of view have not been published in neuroscience journals and their articles are not
reviewed by neuroscientists. Implying that their argument does not carry weight. He stated that
even if we agree that these micros bubble up all the way to change behavior, all what we produce
is randomness. He contends that proving randomness exists at the microscopic level does not
change the argument about human behavior since randomness is not agency. A random event
does not become a freely chosen event simply because it is unpredictable. This is one of the most
convincing sections of the book.
The second half of Determined is stronger and more consequential because it moves from
abstract theory to lived human behavior. Sapolsky explains how behavior is shaped by causes
operating across different time scales. What happens a second before an action matters. What
happened during childhood matters. Prenatal environment matters. Poverty matters. Trauma
matters. Hormones matter. Sleep matters. Culture matters. Historical conditions matter etc.
Human action, according to Sapolsky, is the final expression of an enormous chain of biological
and environmental events. For instance, take intentions. One of the recurring themes in the book
is that intentions themselves arise involuntarily and there is no second or alternative intent.
Sapolsky argues that the brain begins preparing actions before conscious awareness fully
emerges. What we often experience as a conscious decision may actually be the brain reporting a
decision process already underway. He repeatedly asks the reader to consider a difficult question: where exactly in the chain of neural activity does independent free will enter? His answer is that
neuroscience has never identified such a point.
Sapolsky broadens the argument beyond biology by discussing the impact of culture on behavior.
He explains that behavior is shaped not only by genes and neurons but also by social systems and
historical traditions. Cultural values influence cooperation, punishment, aggression, shame,
honor, and even perception itself. In one society collectivism may be encouraged, while another
may celebrate radical individualism. Some societies normalize retributive violence while others
suppress it. Culture enters the biology of behavior through repeated experience and social
learning.
The moral implications of the book are far more important than the scientific debate itself.
Sapolsky’s central question is not simply whether free will exists. It is what justice means if free
will does not exist. If human beings do not ultimately choose the biological and environmental
conditions that shape them, then how should society respond to crime, failure, achievement,
addiction, violence, or success?
One of the biggest objections to free will is that it will be difficult if not impossible for society to
exist and function morally and ethically unless we make people responsible for their action. One
can argue that virtues like motivation, responsibility and frameworks such as ethics, law and
order which are the foundation of civilization, will not exist. Sapolsky argues that such concerns
arise from confusing causation with excuse (pp. 391-392). He argues that explaining someone’s
behavior does not excuse him/her from the consequences of his actions. Denying the existence of
free will should not lead to letting violent criminals roam around freely until they hurt their next
victim. He objects to retributive justice and supports the state’s obligation to guarantee the safety
of its citizens. He advocates a justice system that is compassionate and oriented towards
correction than punishment.
Sapolsky meticulously elaborated the process on how the mind makes decisions and clearly
developed his argument. He addressed complicated and counter intuitive issues. He also
effectively weakens the traditional concept of free will. However, there are some outstanding
issues that he has not fully resolved.
First, the practical problem of responsibility. Human societies still require systems of
accountability. Parents still need to raise children. Schools still need discipline. Courts still need
judgment. Governments still need laws. Even if moral hatred is unjustified, society cannot
function without consequences.
Second, it appears that there is an inherent inconsistency in his argument. He wants readers to
become more compassionate, less punitive, and less judgmental. But if human beings are fully
determined, then even the act of changing one’s moral outlook is itself predetermined.
Third, the book occasionally becomes repetitive. Sapolsky sometimes returns to the same
conclusion through slightly different examples. The scientific detail is impressive, but there are
sections where the argument could have been presented more concisely. Still, this may partly
reflect the difficulty of convincing readers to abandon such an emotionally powerful belief as
free will.
Despite these limitations, Determined is one of the most important books written in recent years
on human behavior and moral responsibility. Whether one agrees with Sapolsky completely or
not, the book forces serious reflection. It challenges simplistic moral judgment and pushes the
reader to think more carefully about the causes of human action.
My own view is that Sapolsky succeeds in demonstrating that human behavior is far more
determined than most people are willing to admit. He also makes a compelling argument against
cruelty, excessive punishment, and self-righteous moral thinking. However, I am not fully
convinced that free will can be dismissed entirely in practical human life. Even if free will is
limited, constrained, or biologically conditioned, societies still require some working concept of
responsibility.
In conclusion, the most valuable contribution of Determined is not necessarily in
convincing readers that free will does not exist, but rather in raising our consciousness
about what it would mean to live in a society that accepts the absence of free will. If
human behavior is largely shaped by forces beyond individual control, then society
should become more compassionate and less cruel or vindictive. In my view, this is the
most important contribution of the book.