 The earliest studies attempted to document the action of natural selection in wild populations in support of Darwinian’s theory. In so doing, these studies attempted to demonstrate that evolution by natural selection was not only an historical causal force, but that it also continued to act on the characteristics of wild populations in the present day. Under the assumption of gradualism, it was not clear whether natural selecting acting on phenotypes in wild populations could be detected, let alone account for between species phenotypic differences. The starting observations of many of the earliest ecological genetic investigations, i.e., the phenotypes of most interest, were conspicuous phenotypic polymorphisms, such as the spotting patterns on butterfly wings or banding patterns of snail shells or polymorphisms of chromosomal rearrangements. These were either known to have a genetic basis or could safely be assumed to have one.