Zhu Chen, Zhang Xiaohui, Zhao Qiran, Chen Qihui
College of Economics and Management, China Agricultural University, Beijing 100083, China; Institute for Population and Labor Economics, Chinese Academy of Social Sciences, Beijing, China.
School of Life Sciences, Nanjing University, Nanjing, Jiangsu, China.
Econ Hum Biol. 2018 May;29:102-114. doi: 10.1016/j.ehb.2018.02.008. Epub 2018 Feb 19.
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 (the "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. Concerning potential endogeneity of hybrid marriages, we conduct a series of robustness checks. Reassuringly, the estimated heterosis effect remains significantly positive across various measurements, after controlling for parental educational attainments/height, environmental influences, and over a thousand region and region-by-year fixed effects. The effects in male and higher-educated offspring are found to be stronger. Results are replicated when analyzing body height using data from the China Health and Nutrition Survey. Although endogeneity of "hybrid marriages" may not be completely ruled out, the current study sheds light on the potentially beneficial effects of interprovincial migration on population-level human capital accumulation, and we hope that this paper can intrigue future studies that further address endogeneity. 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 the overall genetic influences of parents on offspring's performance may be further decomposed into a conventional heredity effect and a heterosis effect that has been neglected previously.
在遗传学中，杂种优势是指物种内杂交产生的后代在遗传上比其亲本更具适应性，并表现出改善的表型特征的现象。基于杂种优势理论和现有的遗传证据，“混血”婚姻（配偶来自不同的州/省/国家/地区）的后代，尽管由于地理界限相对罕见，但在智力、身高或身体吸引力方面可能表现出更大的遗传适应性（“距离-表现”假说）。本研究通过将高维固定效应（HDFE）建模框架应用于2000年中国人口普查数据中独特的0.1%微观样本，探讨杂种优势是否是影响中国后代教育成就的一个因素。关于混血婚姻的潜在内生性，我们进行了一系列稳健性检验。令人放心的是，在控制了父母的教育程度/身高、环境影响以及一千多个地区和逐年固定效应后，估计的杂种优势效应在各种测量中仍然显著为正。发现对男性和受过高等教育的后代的影响更强。使用中国健康与营养调查的数据分析身高时，结果得到了重复。尽管“混血婚姻”的内生性可能无法完全排除，但本研究揭示了省际迁移对人口层面人力资本积累的潜在有益影响，我们希望本文能激发未来进一步解决内生性问题的研究。因此，从进化的角度来看，隐含的杂种优势效应可能对智人这个物种具有深远意义。另一个重要的含义是，父母对后代表现的总体遗传影响可能进一步分解为传统的遗传效应和以前被忽视的杂种优势效应。
