Evolution of coexistence in a crowded microplate well

Understanding what causes the emergence and maintenance of biological diversity has been a central aim in biology ever since the dawn of the discipline. The realization that diversity in microbial communities, such as those living in our guts and on our bodies, may affect our health and that of the agricultural systems on which we depend has generated substantial recent efforts to describe the extraordinary diversity of microbial communities. However, efforts to understand the ecological and evolutionary mechanisms responsible for generating and maintaining all this diversity have severely lagged behind those to describe it. This is unfortunate and unnecessary. Microbes offer a great opportunity to rigorously test hypotheses about these mechanisms in real time in controlled experiments in the laboratory. As Frenkel et al. (1) show in PNAS, such experiments may also reveal novel mechanisms of diversification and coexistence—in their case one where the avoidance of crowding plays a key role.