Genetic Influence Helps Explain Variation in Human Fertility: Evidence From Recent Behavioral and Molecular Genetic Studies

To search for genetic influence on human fertility differentials appears inconsistent with past empirical research and prior interpretations of Fisher's fundamental theorem of natural selection. We discuss Fisher's theorem and give reasons why genetic influences may indeed account for individual differences in human fertility. We review recent empirical studies showing genetic influence on variance in fertility outcomes and precursors to fertility. Further, some of the genetic variance underlying fertility outcomes overlaps with that underlying fertility precursors. Findings from different cultures, different times, different levels of data, and both behavioral and molecular genetic designs lead to the same conclusion: Fertility differentials are genetically influenced, and at least part of the influence derives from behavioral precursors that are under volitional control, which are themselves genetically mediated.