September 24, 2009

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


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.



Andrew Lancaster said...

The lingering fascination some authors have with of using words other than "clade" and then worrying about which is the right "level" (genus, species, race) is in conflict with Darwinian evolutionary science. There are no fixed "levels" defined by nature, they are all only nominal and temporary. If you just call them all clades you get rid of a lot of confusion and a lot of unnecessary debate. It would also help writers whose interests are scientific from inadvertently giving fuel to pseudo scientific internet racism.

Anonymous said...

Racism has little to do with race. Racism is just a form of bigotry, an excuse to hate, loosely based on different racial phenotypes but all it leads to is a preoccupation with extreme racial stereotypes, e.g The standard for being Caucasian is solely based on silly and unimportant attributes, though genetic, as eye color or other pigmentation issues. Physical Anthropologists have gotten a lot of flak just for seeing that certain black skinned humans have a Caucasoid appearance or that not all Africans are Negroid. Genetic studies have proven those Anthropologist to be correct. And those poor Egyptians, and North Africans labeled as immigrants as they are not dark enough. Can't even use certain words like Negroid. Instead lots of silly euphemisms. Yet American discussion and statistics are all about race and skin color. You can't be born, married or buried in that country without your race being entered on some form. You often read silly statements like "there are many lighter skinned Black Africans lighter than many dark Europeans (Italians etc), of course written by some poorly educated person of a rich mostly mixed North European ancestry, from a country in the Western Hemisphere. I have traveled widely and I have never seen a mass of black Africans lighter in skin than any Europeans. They never prove their statements.

Yes race has a social context especially for mixed race people who see themselves as practically unmixed and belonging to the non European race. In Australia most Aborigines are mixed race and whom the non mixed persons who are Aborigines call derisively Yellows, due to their skin coloration. They don't accept them as they have not become men or women under their Law, they are in effect nobodies.

Anybody who has studied biological taxonomy can see that humans have racial divisions similar to the races in animals.

terryt said...

"and (ii) that human taxonomic differences warrant the rank of species".

We could immediately reject that on the grounds that one of the definitions of separate species is populations that cannot produce fertile offspring. All living humans groups are capable of that, so not separate species.

"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".

Probably so for most other genera also, although some claim nearer to just one million years. Anyway either time is shorter than that between the separation of modern human and Neanderthal. Therefore unlikely to be separate species. We have to come up with some other explanation for Neanderthal extinction.

"There are no fixed 'levels' defined by nature, they are all only nominal and temporary".

I've been arguing exactly that at Maju's blog. He seems to think species and subspecies are set in concrete the moment they are first formed.

"Racism is just a form of bigotry, an excuse to hate".


Anonymous said...

Certain different species can produce fertile offspring nearly 100% of the time. Coyotes and wolves are one example. This is a big misconception about genetics. There are also many species within the same genus that can produce fertile offspring on occasion.