Scott shares humorous anecdotes about the daily chaos of raising toddler twins, from emergency police visits triggered by screaming over the wrong version of a song, to elaborate bedtime battles and the children's obsession with identifying vehicles and animals. Longer summary

Scott Alexander shares entertaining stories about parenting his toddler twins, Kai and Lyra, describing life with them as a 'permanent emergency'. The post opens with police arriving after a 911 call likely triggered by screaming over the wrong version of 'Mister Golden Sun'. Scott describes how the children have developed their own names for songs, their obsession with identifying animals and vehicles (which he theorizes relates to hunter-gatherer instincts), and their different personalities - Kai being chaotic and disruptive while Lyra is calm and cooperative. He details the elaborate bedtime ritual with Kai, including various stalling tactics like demanding food and fake-drinking milk. The post includes several photos of the twins and maintains a humorous, self-deprecating tone throughout while exploring how toddler behavior might reflect evolutionary programming. Shorter summary

Scott examines a new genetic study on missing heritability that both hereditarians and nurturists claim vindicates their position, concluding that despite the study's advances, the fundamental debate over how heritable traits like IQ actually are remains unresolved. Longer summary

This post discusses a new genetic study that attempted to resolve the "missing heritability" debate - the gap between high heritability estimates from twin studies (50-80%) and low estimates from molecular genetic studies (10-20%). The study used whole-genome sequencing to include rare genetic variants and found they could account for about 88% of expected heritability, but the actual heritability estimates themselves were only medium (30-40%). Both hereditarians and nurturists claimed victory: hereditarians because the gap was closed (proving the genes exist), nurturists because the total heritability found was still lower than twin studies suggested. Scott examines both sides' arguments, including measurement error corrections and various confounders, and concludes that despite everyone's claims, the debate remains fundamentally unresolved as different methods continue producing different estimates with no clear explanation why. Shorter summary

Scott Alexander refutes Stephen Skolnick's theory that schizophrenia is caused by gut microbes rather than genetics, showing why the evidence better supports schizophrenia being a complex genetic neurodevelopmental disorder. Longer summary

Scott Alexander responds to Stephen Skolnick's theory that schizophrenia is caused by gut microbes rather than genetics. He systematically dismantles Skolnick's arguments by showing that twin concordance rates are exactly what we'd expect from a genetic condition, that microbiological inheritance patterns don't match schizophrenia inheritance patterns, and that the gut bacteria evidence cited was likely caused by antipsychotic medication rather than being causative. He concludes by explaining why schizophrenia is best understood as a complex neurodevelopmental disorder with multiple contributing factors rather than having a single cause. Shorter summary

Scott explores the 'missing heritability' problem in genetics, where twin studies show traits like IQ and educational attainment are highly heritable but newer genomic methods find much lower heritability, analyzing various potential explanations for this discrepancy. Longer summary

The post examines the 'missing heritability' problem in genetics, where twin studies consistently show behavioral traits like IQ and educational attainment are substantially heritable (around 40-60%), while newer genomic methods find much lower heritability (around 15-20%). Scott reviews the history of behavioral genetics research, explains various study methodologies and their potential biases, and analyzes different hypotheses for this discrepancy. He examines whether twin studies might be flawed, whether newer methods might be missing important genetic effects, and whether educational attainment might be an unusually problematic trait to study. While acknowledging remaining mysteries, he tentatively concludes that twin studies are probably largely correct and that newer methods may be missing rare variants and genetic interactions. Shorter summary

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