Analysis of DNA variation is a powerful tool for detecting adaptation at the genomic level. The contribution of adaptive evolution is evident from examples of rapidly evolving genes, which represent the likely targets for strong selection. More subtle adaptation is also an integral component of routine maintenance of gene performance, continuously applied to every gene. Adaptive changes in the population are accomplished through selective sweeps, i.e. complete or partial fixation of beneficial alleles. The evidence is accumulating that selective sweeps are quite frequent events which, together with associated genetic hitchhiking, represent dominant forces that influence molecular evolution by shaping the variability pattern in the genome.