This paper shows how a shorter fecundity horizon for females (a biological constraint) leads to age and educational disparities between husbands and wives. Empirical support is based on data from a natural experiment commencing before and ending after China's 1980 one-child law. The results indicate that fertility in China declined by about 1.2-1.4 births per woman as a result of China's anti-natalist policies. Concomitantly spousal age and educational differences narrowed by approximately 0.5-1.0 and 1.0-1.6 years respectively. These decreases in the typical husband's age and educational advantages are important in explaining the division of labor in the home, often given as a cause for the gender wage gap. Indeed, as fertility declined, which has been the historical trend in most developed countries, husband-wife age and educational differences diminished leading to less division of labor in the home and a smaller gender wage disparity. Unlike other models of division of labor in the home which rely on innately endogenous factors, this paper's theory is based on an exogenous biological constraint.