Hybrid Marriages and Phenotypic Heterosis in Offspring: Evidence from China

In genetics, heterosis refers to the phenomenon that cross-breeding within species leads to offspring that are genetically fitter than their parents and exhibit improved phenotypic characteristics. Based on the theory of... [ view full abstract ]

In genetics, heterosis refers to the phenomenon that cross-breeding within species leads to offspring that are genetically fitter than their parents and exhibit improved phenotypic characteristics. Based on the theory of heterosis and existing genetic evidence, offspring of “hybrid” marriages (spouses originating from different states/provinces/countries/areas), though relatively rare due to physical boundaries, may exhibit greater genetic fitness in terms of intelligence, height, or physical attractiveness (“distance-performance hypothesis”). This study explores whether heterosis is a contributing factor to offspring’s educational attainment in China by applying a high-dimensional fixed effects (HDFE) modelling framework to the unique 0.1% micro-sample of the 2000 Chinese Population Census data (N = 1,180,111). Concerning potential endogeneity of hybrid marriages, we conduct a series of robustness checks. Reassuringly, the estimated heterosis effect remains positive and significant among various measurements and holds after controlling for genetic heritability, environmental influences, and over a thousand region and region×year fixed effects. Similar patterns are observed for both genders, although the effect for male offspring is generally stronger. Results are replicated when analyzing physical height using data from the China Health and Nutrition Survey. The current study sheds light on the potentially beneficial effects of interprovincial migration on population-level human capital accumulation. The implied heterosis effect could, therefore, be profound for Homo sapiens as a species from an evolutionary point of view. An additional important implication is that, besides environmental factors, the overall genetic influences of parents on offspring’s performance may be further decomposed into a conventional heredity effect and a heteriosis effect that has been neglected previously.