Museum visitors are an ideal population for assessing the persistence of the conceptual barriers that make it difficult to grasp Darwinian evolutionary theory. In comparison with other members of the public, they are more likely to be interested in natural history, have higher education levels, and be exposed to the relevant content. If museum visitors do not grasp evolutionary principles, it seems unlikely that other members of the general public would do so. In the current study, 32 systematically selected visitors to three Midwest museums of natural history provided detailed open-ended explanations of biological change in seven diverse organisms. They were not told that these were evolutionary problems. Responses were coded as: "informed naturalistic" reasoning, featuring some understanding of key evolutionary concepts, "novice naturalistic" reasoning, featuring intuitive explanations that are also present in childhood, and "creationist" reasoning, featuring supernatural explanations. All visitors were mixed reasoners, using one or more of these patterns in different permutations across the seven organisms: 72% used a combination of informed naturalistic reasoning and novice naturalistic reasoning, while a further 28% added creationist reasoning to this mix. Correlational analyses indicated that for many visitors these reasoning patterns were coherent rather than fragmented. The theoretical model presented in this article contributes to an analysis of the developmental and cultural factors associated with these patterns. This could help educators working in diverse educational settings understand how to move visitors and students toward more "informed" reasoning patterns. (Contains 6 figures and 7 tables.)