Cannus stannous: Understanding Chance & Necessity in Natural Selection

This classroom activity highlights how evolution by natural selection is nonteleological—that is, not guided by need, by organismal intent, by inherent progress, by an external ideal, or by any observable purposive agent. Rather, it is driven by chance opportunity, environmental context, and historical happenstance. Students simulate the evolution of a population of tin cans, based on temperature retention/loss in either arctic or hot desert habitats. Chance and necessity interact in separate lab groups (as isolated populations), based on similar starting organisms. The process demonstrates not only selection but also how even organisms in similar environments may not evolve with identical traits, depending on available mutations. It shows that even when selection occurs, it may not do so consistently or uniformly with each generation. It shows both divergence based on different contexts of selection and variability based on the vagaries of history.