Is Homo Sapiens Polytypic?

An interesting paper worth reading, which considers the idea that Homo sapiens can be subdivided to subspecies against two diametrically opposite ideas, namely (i) that there are no human subspecies, and (ii) that human taxonomic differences warrant the rank of species. The author rejects (i) on the grounds that Homo sapiens exhibit higher levels of diversity (in terms of heterozygosity and Fst) compared to species where subspecies are recognized. I had not heard of (ii) argued recently, but Woodley cites Fuerle as a recent supporter, offering the following criticism:

FST reflects the relative amount of total genetic differentiation between populations, however different measures of genetic distance involving mtDNA and autosomal loci are simply inappropriate for the purposes of inter-specific comparison as the different genes involved will have been subject to markedly different selection pressures and are therefore not likely to have diverged at the same time [62]. To illustrate this point, this author listed alternative estimates of the distance between the gorilla species and the common chimpanzee and bonobo, based on various nuclear loci and autosomal DNA. The much higher numbers reflect the extreme variation that can be expected when different genes are considered. Fuerle’s presentation of the data is also problematic for another reason, namely he makes no mention of the current debates surrounding gorilla and chimpanzee/bonobo taxonomy; as new research on these taxa regularly generates novel and in some cases wildly variable estimates of genetic distance between these primates, and there is even some debate over whether the eastern and western gorillas are separate species [60].

Curnoe and Thorne have estimated that periods of around two million years were required for the production of sufficient genetic distances to represent speciation within the human ancestral lineage [56]. This indicates that the genetic distances between the races are too small to warrant differentiation at the level of biological species, as the evolution of racial variation within H. sapiens started to occur only 60,000 years ago, when the ancestors of modern humans first left Africa.

Personally I think that the evidence is clear that human races or subspecies exist, but the discovery that geographic differentiation exists at the level of races, ethnic groups, sub-ethnic groups, and that even villages can be subdivided into geographically distinguishable clusters, make renewed effort into formalizing taxonomy at the sub-species level an especially worthwhile endeavor.

Medical Hypotheses doi:10.1016/j.mehy.2009.07.046

Is Homo sapiens polytypic? Human taxonomic diversity and its implications

Michael A. Woodley

Abstract

The term race is a traditional synonym for subspecies, however it is frequently asserted that Homo sapiens is monotypic and that what are termed races are nothing more than biological illusions. In this manuscript a case is made for the hypothesis that H. sapiens is polytypic, and in this way is no different from other species exhibiting similar levels of genetic and morphological diversity. First it is demonstrated that the four major definitions of race/subspecies can be shown to be synonymous within the context of the framework of race as a correlation structure of traits. Next the issue of taxonomic classification is considered where it is demonstrated that H. sapiens possesses high levels morphological diversity, genetic heterozygosity and differentiation (FST) compared to many species that are acknowledged to be polytypic with respect to subspecies. Racial variation is then evaluated in light of the phylogenetic species concept, where it is suggested that the least inclusive monophyletic units exist below the level of species within H. sapiens indicating the existence of a number of potential human phylogenetic species; and the biological species concept, where it is determined that racial variation is too small to represent differentiation at the level of biological species. Finally the implications of this are discussed in the context of anthropology where an accurate picture of the sequence and timing of events during the evolution of human taxa are required for a complete picture of human evolution, and medicine, where a greater appreciation of the role played by human taxonomic differences in disease susceptibility and treatment responsiveness will save lives in the future.

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