Birth order linked to 150 health conditions in 10-million-sibling study

A large-scale analysis of ten million American sibling pairs has revealed that birth order — whether a child arrives first, middle, or last into a family — correlates with susceptibility to roughly 150 distinct health conditions, including ADHD and autism. The finding does not establish cause, but its sheer scale lends it unusual credibility, suggesting that the position a child occupies within a family is not merely a social fact but may carry biological and developmental weight. It is a quiet reminder that the circumstances of our earliest arrivals — who came before us, who came after — may