Psychopathy: The Substrate

Dawn Drescher's second article in the 'Psychopathy: The Substrate' series on LessWrong (May 2026) dives into the genetic and neurological foundations of psychopathy – the G and N levels of their multi-level framework. At the genetic level, twin studies show callous-unemotional traits are moderately to highly heritable (40-70%), though this includes gene-environment correlations. Specific candidate genes like MAOA (the 'warrior gene'), 5-HTTLPR (serotonin transporter), OXTR (oxytocin receptor), and COMT (dopamine regulation) have been associated with small effect sizes. However, the author stresses that most psychopathy is polygenic – many variants each contributing a little – and genetic testing cannot diagnose someone. They propose three parsimonious G-level categories: G-callous, G-impulsive, and G-reactive, which can co-occur.

At the neurological level, the classic finding is reduced amygdala activity and/or volume, impairing fear processing and emotional learning. This brain structure's hypoactivity is considered a key substrate for the emotional deficits seen in psychopathy. The article emphasizes that genetics and neurology form the 'substrate' but don't determine outcomes – environment shapes presentation. The distinction between primary (biologically driven) and secondary (environmentally shaped) psychopathy has major implications for prognosis and intervention. This detailed analysis provides a scientific grounding for understanding the disorder without falling into biological determinism.