methods to human fertility (Rodgers et al., 2001b) and race differences in birth weight (van den Oord and Rowe, 2000).

The controversy that can occur when disciplinary boundaries are crossed in the consilience process is illustrated by the responses to the van den Oord and Rowe paper in a later issue of Demography (Frank, 2001; Zuberi, 2001).¹ Similarly, a paper by Morgan and King (2001) that reviews the biological predispositions, social coercion, and individual incentives for having children in contemporary below-replacement fertility contexts resulted in diverging opinions about the usefulness of biodemographic or behavioral genetics approaches in understanding contemporary fertility behavior (Kohler, 2001; Capron and Vetta, 2001).

The idea that the disciplinary boundary can be crossed in either direction suggests two very different questions: What does genetics have to contribute to demographic research on fertility? What can demography contribute to a geneticist’s thinking about fertility? These questions cannot easily or naturally be addressed together because the specificity of the models and theories in the two disciplines are at such completely different levels. Further, Wilson (1998:198) implied that an asymmetry exists in how the goals of consilience will be received by the two disciplines. In comparing medical science to social science, he stated, “The crucial difference between the two domains is consilience: The medical sciences have it and the social sciences do not.” If he is correct, we can infer that genetics, as emergent from medical science, would be more naturally disposed to such an integrative and cross-disciplinary effort than demography, a social science.

We take the position that consilience is a positive development, that cross-disciplinary research has the potential to generate methods and models that are far beyond the sum of the separate contributions. Those more strongly wedded to a focal disciplinary perspective will undoubtedly be uncomfortable with our specific and also with broader efforts toward consilience. In this paper we are concerned primarily with the issue of how designs and methods that emerge from genetics research (more specifically from behavioral genetics) can contribute to demographic thinking about fertility. In particular, in this specific study we apply behavioral genetics methods to study the relationship of education, fertility, and heritability of fertility.

Before embarking on these specific analyses, we briefly consider the second question: Can demographic methods inform genetics research? In a sense the answer to that question is embedded in population genetics, and that interplay has been occurring for quite some time. Population geneticists are, fundamentally, demographers at heart. Accounting for the distri-