Much of the language of racial science and theory derived from the world of plant and animal husbandry. This legacy may be most obvious in the analyses produced by racial thinkers about “racial mixing,” or miscegenation. Racial thinkers spoke about pure and hybrid races, about inbreeding and crossbreeding. A species was defined by natural science in terms of reproduction: members of the same species were capable of reproducing with one another. Though few seriously doubted that the races, no matter how different, could reproduce, many wondered if different races could breed together to any lasting effect. In other words, could different races produce offspring that would survive as hybrids over a generation or more? Moreover, could races that were significantly different from one another produce healthy offspring? Jewish and non-Jewish racial thinkers asked such questions about the Jews. Of course Jews could mate with Christians, but were such unions less fertile? Did they produce fewer offspring on average? And were these offspring less fit?
As we have seen, questions about Jewish racial purity and mixing constitute a crucial component of many—perhaps most—of the texts in this volume. Jewish thinkers engaged the issue by exploring the history of Jewish and non-Jewish encounters, beginning in the biblical period and moving into the present. To what extent did Jews mix their “blood” with foreigners? This question entails asking about sexual relations in many guises: intermarriage, but also extramarital relations, either freely entered into or not (as a result of conquest, enslavement, and so forth). It also includes conversion, particularly during those periods of Jewish history when gentiles converted in appreciable numbers to Judaism.