The origin of adaptive phenotypes

equences of DNA provide documentary evidence of the evolutionary past undreamed of by pioneers such as Darwin and Wallace, but their potential as sources of evolutionary information is still far from being realized.A major hindrance to progress has been confusion regarding the role of positive (Darwinian) selection, i.e., natural selection favoring adaptive mutations.In particular, problems have arisen from the widespread use of certain poorly conceived statistical methods to test for positive selection (1, 2).Thousands of papers are published every year claiming evidence of adaptive evolution on the basis of computational analyses alone, with no evidence whatsoever regarding the phenotypic effects of allegedly adaptive mutations.But it would be a mistake to dismiss Yokoyama et al.'s (3) study, in this issue of PNAS, of the evolution of visual pigments in vertebrates as more of the same.For, unlike all too many recent papers in the field, this study is solidly grounded in biology.