Scott Alexander uses simulations to explain why seemingly counterintuitive arguments against the genetic basis of schizophrenia are misleading. Longer summary

Scott Alexander discusses two seemingly counterintuitive arguments against the genetic basis of schizophrenia and explains why they're not as compelling as they might appear. He uses a simplified simulation to demonstrate how a highly heritable disorder can have low twin concordance rates and why eliminating affected individuals doesn't significantly reduce prevalence in the next generation. The post aims to clarify common misunderstandings about polygenic disorders and their inheritance patterns. Shorter summary

Scott Alexander explores new data on birth order effects among his blog readers, finding social factors likely explain firstborns' overrepresentation. Longer summary

Scott Alexander revisits the birth order effect he discovered in his blog readership in 2018, presenting new data from a 2020 survey. He confirms the original findings that firstborns are overrepresented among his readers, especially when age gaps between siblings are small. The post explores potential explanations, concluding that social factors, particularly parental attention, likely play a larger role than biological factors. This challenges some established views on the impact of early childhood experiences on adult outcomes. Scott acknowledges limitations in his analysis and calls for further research to better understand these effects. Shorter summary

Scott Alexander discusses a study challenging the idea that childhood abuse lowers IQ, and explores its implications for understanding the effects of child abuse on various outcomes. Longer summary

This post discusses a study by Danese et al. challenging the assumption that childhood abuse lowers IQ. The study found that after adjusting for pre-existing factors, there was no significant difference in IQ between abused and non-abused children. Scott Alexander explores the implications of this study in the context of shared-environment-skeptical psychiatry and discusses other studies showing limited effects of child abuse on various outcomes. He notes that while these findings are interesting, they may understate the dangers of severe abuse due to sample size limitations. The post concludes by suggesting that child abuse likely causes PTSD-like symptoms but may not have effects drastically different from normal PTSD. Shorter summary

Scott examines conflicting evidence on whether humans choose mates based on parental imprinting or genetics, concluding that mate choice might be based on mysterious romantic love. Longer summary

This post explores the question of how humans choose their mates, examining theories of imprinting on parents versus genetic influences. It reviews several studies on animals and humans, including twin studies, that provide conflicting evidence. The post starts by discussing psychoanalytic theories and animal studies supporting imprinting, then moves to human studies with mixed results. It then examines twin studies that surprisingly show little genetic influence on mate choice. The post ends with the suggestion that mate choice might be based on romantic love, which is beyond scientific understanding. Throughout, Scott maintains a skeptical and sometimes humorous tone, highlighting the complexity and contradictions in the research. Shorter summary

The post argues that 'non-shared environment' in twin studies is often misunderstood, encompassing more than just different experiences and potentially overestimating the impact of nurture on personality and life outcomes. Longer summary

This post discusses the concept of non-shared environment in twin studies, arguing that it's often misinterpreted. The author explains that the 50% attributed to non-shared environment in many twin studies isn't solely about different experiences, but includes measurement error, random chance, and biological factors. The post breaks down various components of non-shared environment, including measurement error, luck, biological noise, immune system differences, epigenetics, and genetic mutations. The author suggests that the actual impact of different experiences (nurture) on personality and outcomes may be smaller than commonly believed, citing a review by Eric Turkheimer. The post concludes by suggesting that this interpretation could mean nature is more important than previously thought, making social interventions more challenging and genetic engineering more tempting. Shorter summary

Scott Alexander defends the validity of intelligence and IQ tests by comparing them to comas and the Glasgow Coma Scale in medicine. Longer summary

Scott Alexander argues that intelligence and IQ tests are valid concepts, analogous to comas and the Glasgow Coma Scale in medicine. He contends that whether there's a single general factor of intelligence is less important than the usefulness of IQ as a predictive measure. Scott draws parallels between how comas and intelligence are measured, showing that both involve multiple factors combined into a single scale used for predictions. He criticizes arguments against the existence of intelligence as often being a motte-and-bailey fallacy, where the easily defensible position (uncertainty about a single general factor) is used to imply that all claims about intelligence are meaningless. Shorter summary