Chapter 16: Biology, the Criminal Justice System, and Free Will

Sapolsky challenges how the criminal justice system conceptualizes responsibility by asking whether free will exists at all. Sapolsky argues that neuroscience undermines the traditional model of punishment, suggesting the system should be rebuilt with biology, not morality, as its foundation. He critiques “mitigated free will,” the belief that people are generally responsible but can be excused when biology overwhelms them. Classic cases such as Daniel M’Naghten’s psychosis-driven assassination attempt in 1842 illustrate how insanity defenses formalized this stance. Yet neuroscience reveals that biology always shapes behavior—whether through genes, prenatal stress, frontal cortex damage, sleep deprivation, childhood trauma, or neurotransmitter fluctuations—meaning the dividing line between culpability and excuse is arbitrary. Sapolsky reviews perspectives ranging from complete free will (rarely defended) to complete determinism, noting that most people embrace a middle ground. He critiques this dualism by showing how even “effort” and “willpower” are biologically constrained. Carol Dweck’s research on praising effort versus intelligence reflects a cultural myth: we assign aptitude to biology and self-control to free will, when in reality both are biological. Examples such as pedophilia versus child molestation, or hearing psychotic voices but resisting them, highlight the problematic division of “urges as biology” and “resisting urges as free will.” The chapter explores neuroscience in the courtroom. While technologies like fMRI, EEG, or implicit bias testing raise questions about evidence and fairness, the deeper challenge is conceptual. Punishment, Sapolsky argues, persists because it feels good: brain imaging shows that deciding to punish activates the vmPFC, amygdala, and dopamine reward pathways. Like public hangings of the past, punishment gratifies limbic circuits more than it serves justice. He urges abandoning punishment as a virtue, retaining only protective incarceration and rehabilitation, while recognizing that deterrence may need to be reimagined. Sapolsky also reviews the Libet experiment, which found that brain activity precedes conscious intention by half a second. While some interpret this as proof that free will is illusory, Libet himself argued for “free won’t”—the capacity to veto impulses before action. Regardless, neuroscience increasingly suggests that choices are shaped by biology and context, not independent homunculi. The chapter concludes with humility. Just as epilepsy was once blamed on witchcraft but is now seen as a disease, future generations will likely view today’s attributions of evil or free will as outdated. Science continually shrinks the space for free will, confining it to trivial decisions if it exists at all. Sapolsky insists that denying free will need not be dehumanizing—it is more humane to see harmful people as malfunctioning systems needing treatment or containment than as sinners deserving torment. Ultimately, recognizing the biology of behavior demands a justice system built not on vengeance but on protection, prevention, and compassion.