How has growing knowledge about human genetics affected how American textbooks present race? This article analyzes 80 biology textbooks published from 1952 to 2002 to reveal that U.S. biology texts have pursued the topic of race with renewed vigor in recent years. Moreover, textbooks have redefined race as genetic without furnishing empirical evidence for this framing. The textbooks' transformation sheds light on the broader relationship between race and science in the United States, where claims about racial difference have not only drawn instrumentally and selectively from empirical research, but at times forgo scientific grounding altogether. As the textbooks show, both the tight and the loose linkage of race to science can preserve the cultural authority of the race concept. The texts also make clear that race is not a one-time construct or a relic of centuries past. Instead, it is continually remade -- and is being reworked today -- suggesting its dynamic adaptation for ongoing use as a fundamental tool of social stratification.