Evolutionary theory serves as the fundamental cornerstone to all life science; yet students frequently possess misconceptions regarding evolution or resist learning the idea altogether. This study, which emerged from a larger project focused on informal reasoning, explores how college students' conceptions of evolutionary theory affect their reasoning in the context of genetic engineering issues. Thirty students, 15 biology majors and 15 non-science majors were interviewed individually and asked about their positions on gene therapy and cloning. Whereas none of the non-science majors alluded to evolution, many of the biology majors (8 of 15) adopted evolutionary perspectives as they negotiated genetic engineering issues. Some student responses revealed misconceptions such as teleological and deterministic interpretations of evolution, but others discussed more appropriate evolutionary implications, such as reduced genetic variability and the propagation of unfit genes as a result of cloning. Applications of these findings for both evolution instruction and assessment are discussed. (Contains 1 figure.)