Racial polyphyletism

Polyphyletic theories of human races are discredited models of human evolution which argue that different races belong to separate lineages and evolved parallel to one another for hundreds of thousands to millions of years. The most recent common ancestor between the races is pushed back far in time, and the races are considered to have sprung from multiple ancestral sources, e.g. different species (Gates, 1948), or a single polytypic species but of considerable time-depth as continental subspecies (Coon, 1962).

M. H. Wolpoff points out that the Multiregional hypothesis of human evolution should not be confused with racial polyphyletism, and blames Stephen Jay Gould for this error:

Since its inception in the 1980s, multiregional evolution has never been polyphyletic. It has always been a theory about intraspecific evolutionary processes with an emphasis on gene flow... Gould consistently misportrayed it and widely publicized multiregional evolution as a polyphyletic model of parallel racial evolution similar to that of Carleton Coon’s in the 1960s. This can never be corrected now, and when Gould was alive, repeated attempts to do so in Natural History, where for the most part his incorrect and misleading depictions regularly appeared, were rejected by an editor.

Background
Before Darwin (B.D.), while there were theories of transmutation of species within biology, most biologists accepted a creationist worldview. The original polygenism vs. monogenism debate therefore focused on whether all human races descend ab initio (from the beginning) from Adam and Eve, or whether some descend from other ancestors such as Pre-Adamites. After the publication of The Origin of Species in 1859, biologists incorporated common descent into their study of animals, including humans. However, the polygenism vs. monogenism issue did not disappear but shifted to a debate as to whether human races share recent or archaic common ancestry. Polyphyletism as a form of evolutionary polygenism emerged to argue that distinct human races are millions of years old and evolved in parallel (as separate lineages) from the Miocene, Pliocene or Early Pleistocene:

Most forms of evolutionary polygenism recognize monophyly, a common ancestry for the human races extending far back into antiquity. These polygenist theories differ from monogenism that just postulates a distant common ancestor in that they suggest that the races were separated for so long they acquired their humanity independently, either through parallelism or some kind of adaptive convergence... While races were no longer considered products of separate creations; according to these polygenist theories the races are products of independent evolutionary lineages... the polygenists saw races as different species, and some even postulated different anthropoid ancestors for them, pushing back the common ancestor further still. (emphasis in original)

1860s-1940s
Karl Vogt in 1864 first proposed while the different races of man shared an early primate ancestor millions of years ago, they had evolved separately from different apes on the continents. This view was taken up by F. G. Crookshank who argued in The Mongol in our Midst (1924) that the Mongoloid race evolved from the orangutan, the Negroid from the, and the Caucasoid from the chimpanzee. In 1931, the anthropologist Earnest Hooton argued for a Miocene origin of the races from the descendants of dyropithecines:

During the Miocene period a family of giant generalized anthropoid apes, the Dryopithecus family, which was spread over a wide zone in the Old World, evolved into the ancestors of the existing and extinct forms of anthropoid apes and those of several varieties of man: Some of these became the ancestors of extinct human precursors, while others were the progenitors of the lines leading to the present day races of man.

Thomas Griffith Taylor (1937) considered the Negrito to have evolved separately from the other races who descended from the Neanderthal:

I think that the simplest explanation is that the ancestors of the Negrito and Neanderthal types developed independently from the primitive Catarrhine ape-stock, in Pliocene, or even Miocene times.

A late convert to the evolutionary polygenism of human races was Arthur Keith in 1936:

Hooton also influenced Keith. Hooton was exposed to the polygenic interpretations of Roland Dixon (1875–1934), his early mentor when he began work at Harvard in 1913. As discussed in Wolpoff and Caspari (1997), we believe Keith’s late conversion to polygenism, first expressed in an obscure 1936 publication, was informed by Hooton's early thinking based on Dixon's (1923) influence.

In his A New Theory of Human Evolution (1948) Keith argued human races were a single species, but that they had arisen over two million years ago and evolved parallel:

Most evolutionary polygenists like Keith by the 1940s had abandoned or denounced the idea human races were separate species, instead opting to classify them as subspecies, but still with long separate phylogenies. A notable exception was the botanist and geneticist R. R. Gates (1944, 1948) who cited instances of cross-species fertility among plants to argue racial hybridization does not discredit the Australoid, Bushmenoid, Negroid, Mongoloid and Caucasoid races being different species. According to Gates, Homo sapiens is better comparable to a genus taxonomic rank, and the five human races (in his classification) as species. Gates (1948) considered "there have been two more or less independent streams in human evolution":
 * Australoid: Pithecanthropus > Javanthropus soloensis > Wadjak > Australoid
 * Capoid: Africanus njarensis > Homo rhodesiensis > Florisbad > Bushmenoid

While treating these two races (or rather species) as parallel lineages, Gates would derive the Caucasoid, Negroid and Mongoloid stocks from a mixture of fossil sources, allowing for some limited interbreeding between them. In contrast, Hooton's (1946) polyphyletism did not allow for any gene flow between his "major races" at all, only between subraces: "he allowed for reticulation or interbreeding in the formation of what he considered secondary and tertiary racial groups. He believed the essential, primary races emerged through polygenism".

1950s-1980s
Polyphyletic theories of racial origins were criticized by the geneticist Theodosius Dobzhansky from the 1950s. He pointed out that if races had evolved parallel (and isolated to one another) for millions of years, with virtually no genetic exchanges between them, they would no longer be intraspecific races, but species, that could no longer interbreed with each other.

In 1957, the polygenist Robert Gayre citing Gates, argued that Dobhansky's argument is unfounded since there are instances of interfertile species, i.e. different species in the wild that reproduce with one another. He therefore wrote: "if sterility is no test, as such, of speciation, then neither is its converse, interbreed-ability, a test of belonging to the same species" and "since sterility fails as the criteria of species, we have to rely on the traditional basis of morphological differences in the discrimination of species, including man". Gayre regarded Caucasoids, Mongoloids and "Melanoids" (Negroids, Australoids) to be different species, having evolved parallel (with almost no contact for millions of years) on the different continents, and dated their divergence as old as the human-chimpanzee split.

The primatologist Osman Hill in his book Man's Ancestry (1954) wrote:

[T]here seems no reasonable objection to the polyphyletic origin of the human family. That modern man constitutes a single species is arguable. The differences between a Negro and a Mongolian are at least as great as between an ass and a zebra.

Carleton Coon
Carleton S. Coon published The Origin of Races (1962) which defended a polyphyletic view of race, but was less extreme than his predecessors in time-depth. Coon claimed to have traced the origin of five human races to the early Middle Pleistocene, or 750,000 years ago. He also allowed for peripheral or minor gene flow between the races, but not multidirectional. For Coon, it was Caucasoids and Mongoloids who occasionally migrated and mated with Congoids, Capoids and Australoids throughout the Middle and Late Pleistocene, almost never vice-versa:

In Coon's view of human phylogeny each of the main living human races has had its own evolutionary history without, however, having an entirely independent evolution. Indeed, Coon (1962) pointed to a number of instances which might have implied contacts between them. For instance, the transition from Homo erectus to Homo sapiens in the Australoid line was caused by gene flow coming from the Mongoloid line… the Caucasoid line permitted contacts with the Australoid, Congoid and Capoid racial lines.

Coon introduced the concept of "line and grade": each race he considered an ancestor-descendant group that passed through a sapiens state threshold from a more 'brutal' erectus, synonymous with an evolutionary grade. According to Coon, the races are subspecies, and belong to a single polytypic species. However Coon proposed each subspecies or geographical race crossed the sapiens-erectus threshold at different times, five times in total, and could also be classified as phyletic "lines", i.e. independent lineages, minimizing gene flow between them. Dobzhansky criticized Coon's theory in a paper entitled: "Possibility that Homo sapiens evolved independently 5 times is vanishingly small". Coon responded that he "did not state that the subspecies evolved in complete isolation, but that they failed to speciate [separately by branching] because of peripheral gene flow". Coon's model is still polyphyletic, involving parallel evolution, since he proposed differential evolutionary rates for the races crossing the sapiens threshold, i.e. the Congoid line becoming sapien more than 200,000 years after the Caucasoid (this extreme view Dobzhansky pointed out could be taken advantage of by white separatist propagandists); so for Coon, the level of relative isolation between the human races and non-multidirectional gene flow accounted for distinct racial lineages. Caspari and Wolpoff (1996) note:

Coon's use of genic exchanges to explain worldwide trends was always half-hearted and seemingly an afterthought. Genic exchanges were never so important that they were able top revent the hominid subspecies from evolving at different rates and crossing the "sapiens threshold" at quite different times - the essentially polygenist aspect of his thinking was that the different subspecies attained their humanity separately. He never could convincingly solve the problems presented by what appeared to be massive parallelisms in his polygenic scheme.

In 1981, Coon died. His book Racial Adaptations (1982), published posthumously, continued to defend a polyphyletic origin of five races.

In his final book Coon discussed saltationism, struggling to explain how the races crossed the erectus-sapiens threshold (at different times) despite evolving parallel:

Regarding Coon's polyphyletism, Grover Krantz in 1980 wrote:

Some of these [race] lines cannot be convincingly demonstrated, but one clear case… sapiens in eastern Asia the Mongoloid traits continue (Inca bone, shoveled incisors, anterior molars, enamel extensions and pearls, and mandibular tori, to name a few)."

Krantz considered there to have been continuity in non-adaptive skeletal traits in East Asia for up to one million years, and that Mongoloids were "largely unaltered" by migration. He though cautioned that: "I hope no one took this to imply total genetic separation between these lines". Like Coon, Krantz argued for minor non-multidirectional gene flow (some races he thought were more-or-less isolated) and that the races (although contrary to Coon, less than 5, possibly 3) crossed the erectus-sapiens threshold in their continents at different times. In his book Climatic Races and Descent Groups, Krantz wrote a "polyphyletic origin for sapiens is clearly indicated". Krantz (1981) argued that cultural behavior and linguistic ability accounted for sapienization, without having to invoke much, if any, gene flow.

Decline in support
Coon failed to produce an evolutionary mechanism that could explain how human races evolved parallel for hundreds of thousands of years, and yet independently reached the same sapienization grade, from an archaic (erectus) human, to anatomically modern human. Dobzhansky showed this was a problem for all racial polygenists: their ideas of parallelism require a "mystical inner drive that propels evolution". Polyphyletic evolutionary theories of human races also disappeared from the scientific literature after Coon (1982) because human races were shown to be an inaccurate way of studying biological variation: "many physical anthropologists therefore believe that the concept of cline is more useful for research purposes than the race concept".

Modern genetic analyses support a clinal concept of variation between populations (e.g., see the work of Luigi Cavalli-Sforza).

Geneticist Alan Templeton (1998) has shown "genetic evidence strongly rejects the existence of distinct evolutionary lineages within humans":

The Origin of Races (1962) and racial polygenism in general has also been criticized as having racist implications.

Multiregionalism
Wolpoff, et al. (1984) founded the Multiregional hypothesis of human evolution (which covers the Pleistocene). In their first paper, Wolpoff and his colleagues Alan Thorne and Xinzhi Wu reviewed, criticized and rejected the previous polyphyletic models of human races, including Coon's. Instead Wolpoff founded an evolutionary model that argues for a single human species that incorporates multidirectional gene flow between all Old World populations, but with more gene flow from the center of the species range. This model states that the human species emerged 2 million years ago in Africa and spread across the Old World, and that there has been regional continuity spanning the Pleistocene of four "morphological clades", defined not as lineages, but as sets of cranial traits that "uniquely characterise a geographic region". These regional traits were stabilized in peripheral or 'edge' regions on earth through a balance of genetic drift, gene flow and selection.

Multiregionalism has been misinterpreted as evolutionary polygenism, or in particular Coon's model of human origins which Wolpoff and his colleagues have distanced themselves from.