Scott Alexander reviews the evidence for declining sperm counts, discussing major studies, criticisms, and potential causes, while remaining uncertain about the true extent and reasons for any decline. Longer summary

Scott Alexander examines the evidence for declining sperm counts worldwide, discussing the major studies, potential causes, and criticisms of the hypothesis. He explores the methodology of sperm count studies, regional variations, possible explanations like plastics and pesticides, and animal data. While acknowledging the noisy data and potential confounders, he concludes that there's suggestive evidence for a decline but remains uncertain about its magnitude and causes. Shorter summary

Scott Alexander examines studies linking parental age to psychiatric disorders in children, revealing that the father's age at first child, not at conception, is the key factor. Longer summary

Scott Alexander discusses a study in JAMA Psychiatry about the prevalence of psychiatric disorders in relation to parental age. Initially, it seemed that children of young mothers and old fathers were at higher risk. The study proposed that older fathers accumulate more mutations, leading to higher risk of disorders in their children. However, a clever follow-up study found that the risk is more related to how old the father was when he had his first child, rather than the father's age at conception. This suggests that men with mental health issues or risk factors may take longer to find partners and have children, rather than the age itself being the cause. Scott concludes that this finding is sad on a societal level but personally liberating, as he feels less guilty about potentially having children later in life. Shorter summary