Molecular drive: a cohesive mode of species evolution.

It is generally accepted that mutations may become fixed in a population by natural selection and genetic drift. In the case of many families of genes and noncoding sequences, however, fixation of mutations within a population may proceed as a consequence of molecular mechanisms of turnover within the genome. These mechanisms can be both random and directional in activity. There are circumstances in which the unusual concerted pattern of fixation permits the establishment of biological novelty and species discontinuities in a manner not predicted by the classical genetics of natural selection and genetic drift.