Darwinian evolution is difficult to understand because of conceptual barriers stemming from intuitive ideas. This study examined understanding of evolution in 52 students (M = 14.48 years, SD = 0.89) before and after a guided field trip to a natural history museum and in a comparison group of 18 students (M = 14.17 years, SD = 0.79) who did not attend the trip. During the trip, students learned about the "Oxford Evolution Debate." Students were interviewed before and after the trip and were asked about evolutionary processes in humans, algae, seals, finches, and Tasmanian tigers. Students' answers were coded as relying on informed naturalistic reasoning (INR; i.e., some understanding of Darwinian evolution), novice naturalistic reasoning (NNR; i.e., intuitive explanations from folk biology and psychology), and creationist reasoning (CR). Students who attended the trip were more likely to increase their use of INR and decrease their use of NNR than students who did not attend the trip. CR was rarely supported. The majority of both groups of students invoked more than one type of reasoning across the questions. The findings are interpreted in relation to use of multiple epistemologies and the benefits of informal learning environments for increasing understanding of Darwinian evolution.