Scott Alexander examines the paradoxical relationship between autism and intelligence, discussing genetic and environmental factors, and proposing explanatory models for the observed lower IQ in autistic individuals despite genetic links to higher intelligence. Longer summary

Scott Alexander explores the paradoxical relationship between autism and intelligence. While genetic studies show a link between autism risk genes and high IQ, autistic individuals generally have lower intelligence than neurotypical controls. The post discusses three main causes of autism: common 'familial' genes that increase IQ, rare 'de novo' mutations that are often detrimental, and non-genetic factors like obstetric complications. Scott examines various studies and proposes that even after adjusting for mutations and environmental factors, autism still seems to decrease IQ. He introduces a 'tower-vs-foundation' model to explain this phenomenon, where intelligence needs a strong foundation to support it, and an imbalance can lead to autism. The post concludes with a list of findings and their associated confidence levels. Shorter summary