The typical introductory biology curriculum includes the nature of science, evolution and genetics. Laboratory activities are designed to engage students in typical subject areas ranging from cell biology and physiology, to ecology and evolution. There are few, if any, laboratory classes exploring the biology and evolution of human sexual behaviour. Contemporary research in sperm competition provides a template for engaging students in a "sexy" subject at a practical level. We describe and evaluate a laboratory exercise in which students develop and test simple hypotheses about sperm competition in humans. This activity encourages students to think about the nature of science, while they design meaningful experiments in the evolution of human mating systems. Post-laboratory assessment revealed that this exercise was successful in meeting its stated goals, engaging students, stimulating discussion and encouraging thoughtful critique. (Contains 2 figures.)