Behavioral Genetics: New Analysis Highlights Up to 30 Percentage Point Discrepancy in Heritability Estimates

The long-standing "missing heritability debate" in behavioral genetics has seen renewed discussion following recent online entries by prominent commentators. A blog post from Unboxing Politics, highlighted by Alex Strudwick Young on social media, directly challenges the conclusions drawn by Scott Alexander of Astral Codex Ten regarding the corroboration of traditional twin and adoption studies by other genetic methodologies. The core of the contention revolves around differing heritability estimates and the complex influence of assortative mating.

Scott Alexander's recent entry, "Missing Heritability: Much More Than You Wanted To Know," delved into the persistent gap between heritability estimates derived from twin studies and those from molecular genetic approaches. Alexander generally asserted that twin, pedigree, and adoption studies provide robust and validated estimates, stating, "I think the twin / pedigree / adoption estimates are mostly right. They are strong designs, their assumptions are well-validated, and they all converge on similar results." These traditional methods suggest a higher genetic influence on traits like IQ and educational attainment.

In response, Unboxing Politics' piece, "Contra Scott Alexander On Missing Heritability," argues that adoption and pedigree studies do not consistently corroborate twin studies, particularly when accounting for biases. The analysis points to significant discrepancies, revealing that in head-to-head comparisons, "twin study heritability estimates were around 20-30 percentage points higher than adoption study heritability estimates" for traits like IQ. This critique suggests that methodological differences and inherent biases, rather than true genetic effects, may explain perceived convergences.

A key factor complicating the debate is assortative mating, where individuals with similar traits or genetic predispositions tend to partner. Alex Strudwick Young noted this complexity in his tweet, stating, "> Assortative mating as always complicates everything." Unboxing Politics elaborates that assortative mating can bias twin and adoption studies in different directions, making direct comparisons problematic. Newer molecular methods like Relatedness Disequilibrium Regression (RDR), which aim to estimate heritability without environmental bias, consistently yield lower estimates than twin studies, further fueling the methodological dispute.

The ongoing disagreement underscores fundamental challenges in accurately quantifying genetic and environmental influences on complex human traits. The debate calls for a unified analytical approach, applying all methods to large, consistent datasets to resolve discrepancies. Until such comprehensive studies are conducted, the scientific community continues to grapple with the most reliable methods for understanding the intricate interplay of nature and nurture.