The origin of multicellularity was transformative for life on earth, allowing for the evolution of the large, complex organisms we see today. Despite its clear importance, the evolution of multicellularity remains a challenging topic to teach, especially at the high school level. Here we present a quick (one or two 50-min sessions) and easy laboratory in which students experimentally examine the hypothesis that small-mouthed predators can select for multicellularity. Students first observe rotifers and yeast (both unicellular and multicellular strains) separately under the microscope. Based on the observed natural history of the predator, they create a hypothesis for how predation will affect the survival of each type of yeast. They then test this hypothesis by feeding the yeast to the rotifers, quantifying the number of unicellular and multicellular yeast consumed, and analyze this result statistically. Pre-and post-lab assessment demonstrates the efficacy of our hands-on curricula in teaching fundamental concepts about multicellularity, as well as evolution in general.

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