College students with stronger and weaker backgrounds in biology were asked to infer whether one taxon (e.g., a certain reptile) uses the same enzyme to help regulate cell function as comparison taxon A (e.g., a certain amphibian) or comparison taxon B (e.g., a certain mammal). Color pictures of the named taxa were provided. Inferences were made in one of three conditions: Two conditions gave subjects the evolutionary relationships among the taxa (amphibians, reptiles, and mammals in the example), in one of two diagrammatic formats; the third, baseline, condition did not provide such information. Subjects uniformly made the incorrect inference in the baseline condition. Providing the evolutionary diagrams had different effects depending on the diagrammatic format and the biology background of the subjects.