Although the theory of evolution is the foundation of modern biology, students too rarely have an opportunity to watch selection operate in natural populations of animals. This lack may be partially responsible for the unfortunate ignorance of many people regarding the significance of evolution in biology. Laboratory exercises that directly study evolutionary processes can help to increase understanding of the principles of evolution. This article describes a laboratory exercise that focuses on the process of sexual selection. In this exercise, students first go into the field to observe and collect soldier beetles. They use observations they make in the field to develop hypotheses about sexual selection, and then they test their own hypotheses by collecting morphological measurements in the lab. Here, the authors describe the procedure used for testing hypothesis: these instructions include collecting observational data that allow students to determine whether female choice is occurring and whether male-male competition is influencing mating patterns. Following these instructions, the authors briefly discuss other hypotheses that might be tested using similar procedures. (Contains 4 figures.)