"… evolution can be precisely defined as any change in the frequency of alleles within a gene pool from one generation to the next. (Curtis and Barnes 1989, p974)"
"I pointed out more than a decade ago (1977) that the reductionist explanation, so widely adopted in recent decades - Evolution is a change in gene frequencies in populations - is not only not explanatory, but is in fact misleading. Far more revealing is the definition: 'Evolution is change in the adaptation and in the diversity of populations of organisms.'" [Mayr, Toward a New Philosophy of Biology, 1988]