The Linnaean method of classifying races in anthropology was overthrown after Carleton S. Coon’s “The Origin of Races.” His method was similar to that of Buffon. He categorized humans into five races:
Blumenbach had hinted at the continuous (as opposed to discrete) nature of differences among populations, but Coon’s discrete taxonomy won the day. Following Buffon, he described human races in terms of phenotypic distinctives rather than the supposed behavioral differences of Linnaeus. The work was greeted with skepticism, however, towards its purported identification of discrete, Platonic differences among humans, and anthropologists became increasingly concerned with variation among local populations rather than abstract races. It was not simply that there was little to no agreement on how to categorize different races. There did not seem to be any sort of concrete quality by which to distinguish the “races.” Means of distinguishing the groups was arbitrary.
As for Carleton Coon’s work: “Not only was it empirically unsound, but it was pointless as well. the alternative approach acknowledged the apportionment of humans into populations, as had dBuffon in the 218th century, but denied biological reality to the higher-order clusterings of populations, which had been an integral part of the Linnaean approach”(Marks). Sherwood Washburn, preisdent of the American Anthropological Association in 1962 (the year Coon’s work had been published) announced that “process and the mechanism of evolutionary change” had supplanted the “static” approach which emphasized “classification based on types”:
“The concept of race is fundamentally changed if we actually look for selection, migration, and study people as they are (who they are, where they are, how many there are)…Since races are open systems which are intergrading, the number of races will depend on the purpose of classification…”
This “localist” revolution in physical anthropology underwent a further advance in the early 20th century in the work of Earnest Albert Hooton. Hooton was interested in “polymorphism,” or “the biological variation that exists within populations”:
“The study of race is necessarily the study of differences among groups of people. But the relation of the differences that exist among groups to the variation that exists within human groups was uncharted territory at the time…the application of genetic techniques to these questions showed that within-group variation (polymorphism) indeed held the key to understanding biological diversity in the human species. But as long as the focus of the science of human diversity was on “race”, polymorphism would generally be ignored. The emphasis would be on polytypism, the study of the differences among groups, which was the reason for pursuing the study of race in the first place. Hootoon’s insistence on the importance of polymorphism in human populations was thus a crucial advance, though not widely appreciated at the time”(Marks)
Instead of differences among “racial” groups, polymorphism became of increasing interest to academics. Indeed, many would be surprised to learn that, among Mexicans, two individuals with similar melanin content in their skin may be as genetically distinct from one another as a Chinese person is from a Northern European one. While melanin content can, in some cases, be a reliable marker of genetic difference, its reliability is quite variable depending upon the populations under study, and in certain contexts its reliability is modest at best, poor at worst (See the link to the article at the bottom of the page, entitled “Race, genetics and ancestry,” for examples of how unreliable phenotypes such as skin color can be as guides of genotypic difference).
Such racial admixture is the rule, not the exception. All groups are the result of hybridization of various populations. “Miscegenation” is thus either universal or nonexistent:
“…the essentially continuous nature of human variation had been acknowledged, certainly, since Blumenbach; therefore “natural divisions” were all but precluded. As this approach to race seemed to have very little relation to contemporary populations as “mixed races,” the result of extensive hybridization between originally discrete and “pure” populations, resulting in the continuous distribution of features we now encounter”(Marks).
Source: Marks, Jonathan. Human Biodiversity: Genes, Race and History.