Scott Alexander explores how evolutionary processes explain the polygenic structure of schizophrenia and other complex traits, addressing concerns about genetic research and implications for future genetic interventions. Longer summary

Scott Alexander discusses the polygenic nature of schizophrenia and other complex traits, explaining how evolution shapes genetic structures. He presents arguments by E. Fuller Torrey about the lack of large-effect genes for schizophrenia and its persistence despite negative fitness effects. Scott then explores how these seemingly contradictory points actually explain each other: evolution removes large-effect genes, leaving only small-effect genes that accumulate to cause disorders. He discusses three possible reasons for the persistence of these small-effect genes and their implications for genetic selection and engineering. Shorter summary