Kimura. Motoo

In addition to mutation rate, even the other molecular parameters turned out to be different from the expectations of selectionism. It was discovered, for example, that neutral mutations are not in the least a tiny minority with respect to adaptive mutations, and the actual ratio is probably the other way round. At the molecular level, in other words, the dominant mechanism of evolution is not natural selection but genetic drift, and this led Motoo Kimura to formulate the neutral theory of molecular evolution (1968, 1983). 

Two or more genotypes are neutral in evolution when the selection constraint is unable to distinguish between them. Early sequence comparison data [6] apparently confirmed Motoo Kimura s idea of neutral drift in population genetics [5]. Accordingly, many different genotypes could give rise to the same phenotype, and depending on the conditions, different phenotypes can share the same fitness value. Direct evidence for neutral evolution under controlled conditions came only two years ago Se-... 

Motoo Kimura, The Neutml Theory of Molecular Evolution , Cambridge University Press, 1983. 

To make this point more concrete, consider the neutral theory of molecular evolution. As Motoo Kimura rightly points out, under this theory, "Polymorphism (within a species) is just a transient phase of molecular evolution" (Kimura, 1983). Indeed, the neutral theory takes no special accounting of speciation allelic variants within a species are genealogically related to common ancestral sequences (which may or may not be present in the same species) just as allelic variants in different species also have common ancestors further back in time. The topology of an allele genealogy does not change across species boundaries, only the time depth of the tree. 

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