Abstract
One of the principles that has emerged from experimental evolutionary studies of microorganisms is that polymorphic alleles or new mutations can sometimes possess a latent potential to respond to selection in different environments, although the alleles may be functionally equivalent or disfavored under typical conditions. We suggest that such responses to selection in microorganisms serve as experimental models of evolutionary advances that occur over much longer periods of time in higher organisms. We propose as a general evolutionary principle that anagenic advances often come from capitalizing on preexisting latent selection potentials in the presence of novel ecological opportunity.