People interpret genetic causes in two ways: determinism (my genes made me do it) which can be mitigating, or essentialism (my genes are my true self). When people view genes as the 'essence' of a person, a genetic link to bad behavior implies the person is inherently and unchangeably bad, increasing blame rather than sympathy.

Despite decades of research, the core question of "nature versus nurture" in creating a psychopath remains the central unsolved mystery for FBI criminal profilers. While killer Israel Keyes had an abusive childhood, his nine siblings did not become killers, underscoring the complexity and leaving experts without a definitive answer.

Persistently antisocial children often have a biological inability to learn from negative consequences, making them punishment-insensitive but reward-sensitive. Harsh punishment is ineffective and counterproductive, as it destroys the potential for connection, which is the only real leverage for behavioral change.

In cases of extreme violence, we seldom investigate underlying biological factors unless there's an obvious "smoking gun" like a brain tumor. The discovery of a rare MAOA gene mutation causing extreme aggression in a Dutch family raises the question of how often people are labeled as "evil" without any search for an organic cause.

Large-scale genetic studies suggest many distinct brain diseases (mania, depression, ADHD, Alzheimer's) are not separate conditions. Instead, they may be different expressions of a single, general genetic susceptibility to brain dysfunction, which researchers call "Factor P".

Counterintuitively, the heritability of traits like cognition and personality increases from childhood into adulthood. This occurs because individuals increasingly select and shape their own environments based on their genetic predispositions, a process that amplifies the influence of their genes over time.

Genes linked to addiction, impulsivity, and aggression are most active during fetal development, affecting the brain's fundamental balance of inhibition and excitation. This reframes addiction and conduct disorders as neurodevelopmental conditions akin to ADHD, rather than purely as choices or moral failings.

The onset of antisocial behavior before age 10 is one of the biggest predictors of a lifelong pattern of offending. Cold, callous aggression towards others or animals at this young age, often with a heavy genetic component, has a poor prognosis and currently has vanishingly few effective treatments.

Citing research, Sam Harris finds it humbling how little control parents have over their children's character. He states that for most psychological traits, the breakdown is roughly 50% genetic and 50% environmental, but the environmental component is driven by peers and culture, not direct parenting.