On the Origins of Socioeconomic Inequalities: Evidence from Twin Families

Using Danish Twins Registry and population data, we link twins with their relatives to evaluate the controversial assumptions of the classic twin model and decompose socioeconomic inequality into genetic (heritability) and environmental factors. We reject the equal environments assumption, finding that the classic model overestimates heritability. Heritability explains 9% of variation in education and 14-16% in earnings, income, and wealth, helping to fill the ‘missing heritability’ gap between the classic twin model and Genome-Wide Association Studies. Shared environments account for 26-42% of these variances and 45-81% of intergenerational persistence. These findings reconcile estimates from twin and adoptee studies.