For policymakers, the restricted range in twin and adoption studies is a major blind spot. But middle-class parents in First World countries needn’t worry. Families like yours have been studied to death. In your corner of the world, you can safely rely on the postcard version of behavioral genetics: The chief cause of family resemblance is heredity, not upbringing—and while the short-run effects of upbringing are self-evident, they leave little lasting impression.
Small effect sizes might matter alot if were only looking at the fat middle!
