 Even though the population is not evolving, but instead remaining the same over time, it exhibits an adaptation that consists in this persistent lack of change, an adaptation that Darwin thought explicable using his theory. For a more recent and especially compelling case of a selectionist explanation of a polymorphism, see Bayliss, Field, and Moxon’s selectionist explanation of a fimbriae polymorphism produced by contingency genes (Bayliss, Field, &amp; Moxon 2001).