Previous research has demonstrated creationist, Lamarckian, and teleological reasoning in high school and college students. These lines of thinking conflict with the Darwinian notion of natural selection, which serves as the primary catalyst for biological evolution. The current study assessed evolutionary conceptions in non-science majors, freshman biology/environmental science majors, and upper-level biology majors at a small liberal arts college. Results indicate that, prior to instruction, both non-science majors and upper-level biology majors appear to rely heavily on teleological reasoning to explain changes in gene frequencies over time. Instruction that incorporated historical context and avoided teleological language improved student understanding of Darwin's concept of natural selection. (Contains 4 figures.)