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 in consistent with past empirical research and prior interpretations of Fisher 's fundamental theorem of natural selection. We discuss Fisher's theorem an d give reasons why genetic influences may indeed account for individual dif ferences in human fertility. We review recent empirical studies showing gen etic influence on variance in fertility outcomes and precursors to fertilit y. Further, some of the genetic variance underlying fertility outcomes over laps with that underlying fertility precursors. Findings from different cul tures, different times, different levels of data, and both behavioral and m olecular genetic designs lead to the same conclusion: Fertility differentia ls are genetically influenced, and at least part of the influence derives f rom behavioral precursors that are under volitional control, which are them selves genetically mediated.