How family background shapes the relationship between human capital and fertility

Many previous studies have shown that skilled and educated women have fewer children. By comparing twins and close siblings in Swedish register data, we show that the negative association between human capital and fertility mostly reflects family background factors. For males, human capital measures are unrelated to fertility in the overall population, but this again masks the influence of family background factors as high-skilled males tend to have more children than their less-skilled twins or siblings. Hence, family background factors have a strong negative impact on the overall association between human capital measures and fertility for both women and men. Non-cognitive abilities deviate from these patterns—these abilities remain strongly complementary to fertility both within and across families. Our results can be reconciled with a stylized model where family-specific preferences for fertility are shared across generations and shape investments in skills and traits when children are young.