11.19.08. Competition between different strains of bacteria can lead to spacial segregation at the population level (see, for example, Hallatschek et al, PNAS, 2007). Students simulated the competition between a "good" and "bad" strain of bacterium using a number game. Each student started with a certain number of good and bad bacteria; good bacteria were positive and bad bacteria were negative, yielding a total "colony score" that indicated the harmfulness of the population. Colony scores changed by the addition of nutrients (scores doubled) or antibiotics (scores were halved if negative) and by "competition" rounds, in which students combined their scores with neighors' scores. After several rounds, groups of adjacent students tended to converge upon the same score, with some groups finding positive scores and some finding negative scores, illustrating the segration effect.