Elsevier

Medical Hypotheses

Volume 74, Issue 1, January 2010, Pages 195-201
Medical Hypotheses

Is Homo sapiens polytypic? Human taxonomic diversity and its implications

https://doi.org/10.1016/j.mehy.2009.07.046Get rights and content

Summary

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.

Introduction

Historically, the term race has been used in biology as a synonym for subspecies [1], [2]. Whereas the term subspecies was typically used in the description of infra-specific diversity in non-human animal species, the term ‘race’ tends to be employed exclusively in the description of diversity present within the human species. Despite this it is frequently asserted that humans are monotypic (belonging to one species and one subspecies – Homo sapiens sapiens), and that ‘racial’ diversity is either a socially constructed biological illusion or that it exists only at infra-subspecific scales and is therefore taxonomically trivial. In this manuscript a case will be made for the hypothesis that H. sapiens is in fact polytypic and that this has significant implications for fields such as anthropology and medicine.

Four major definitions of what constitutes a subspecies or race have been identified by Long and Kittles [3].

Table 1 illustrates the evolution of classificatory concepts of race from essentialist to lineage based. Although in each case the idea of ‘distinctness’ is invoked as a necessary criterion for the existence of a race there exists considerable disagreement over how to define that distinctness. The essentialist concept of Hooton places the emphasis on the existence of combinations of characteristics shared through common descent, whereas the taxonomic concept uses a combination of phenotypic similarity coupled with the idea of range restriction. The population concept of Dobzhansky on the other hand talks of race exclusively in terms of Mendelian populations whilst the lineage concept of Templeton requires races to have been subject to historical barriers to gene flow whilst simultaneously exhibiting contemporary genetic differentiation.

The table would seem to suggest that there is no universally agreed upon definition of race or subspecies and that the use of any particular race concept in the apportionment of human biological diversity is to a degree arbitrary. This situation has not been helped by inconsistent historical usage in the anthropological literature, where the term would frequently be used in the description of human populations at a variety of scales ranging from sub-continental to global [7].

This suggestion of arbitrariness has led many social scientists to claim that what is termed ‘race’ is in fact nothing more than a ‘social-construct’, devoid of any biological foundation. According to this view, which is known generally as social constructivism, the concept of racial classification is a recent invention (c. 18th century) and was developed as a means of grouping subjugated colonial peoples on the basis of arbitrary physical characteristics. By this logic the very notion of race therefore has inherently racist connotations as, it is inferred, the decision to use concepts of race in the ‘arbitrary’ grouping of humans is suggestive of a desire to delineate an out-group that is some way ‘inferior’ in contradistinction to a ‘superior’ in-group to which, it is presumed, the classifier would belong [8], [9]. As evidence of the pervasiveness of the view that races do not exist within the social sciences, a 1985 survey of 1200 academics who were asked whether they disagreed with the statement: “There are biological races in the species H. sapiens”, revealed that only 16% of biologists disagreed as compared to 53% of socio-cultural anthropologists [10]. The likelihood is that an even higher percentage of social scientists would disagree today. As evidence of this, one only needs to read the official position statements on race and ethnicity of major organizations such as the American Anthropological Association and the American Sociological Association.

The problem with social constructivism is that it attempts to engage racial classification on a normative rather than a scientific level. Using the idea that scientific race concepts stem from a desire to apportion people into ‘inferior’ vs. ‘superior’ categories as grounds for claiming that they are wrong is simply an appeal to motive and therefore is not a logical counter to scientific theories of race, which must be assessed purely on their merits. The notion of arbitrariness in the definition of race is a significant and legitimate scientific issue in need of redress however.

Prior to examining the race concept from a classificatory stand point it is necessary to demonstrate its validity as a biological construct independently of classificatory schemes. It was mentioned previously that all four of the major race concepts require races to be in some way distinct from one another, however it is frequently asserted that because the majority of genetic variation (85%) lies within the classically defined racial groups rather than between them (some estimates indicate that the number is as low as 6%), race is therefore a taxonomically meaningless category. Lewontin, who is the most influential promoter of this hypothesis, essentially assumed that because there is a 30% probability of misclassifying an individual’s race based on the variation in a single genetic locus, race must therefore be taxonomically invalid [11]. Lewontin’s claim was essentially a formalization of the old argument that human populations are too clinal (they share too much variance) to be clearly differentiable into races [12], [13]. Edwards has however countered these arguments with the observation that although Lewontin and others are correct when talking about a single locus or trait, concluding from this that race does not exist is fallacious as the likelihood of not being able to differentiate between racial groups rapidly approaches 0% as more loci or traits are considered. This is due to the fact that loci/trait frequencies within racial groups tend to be correlated [14].

Based on Fig. 1, race and synonymous concepts can be defined as populations expressing a composite number of traits whose distributions intercorrelate in such a way so as to give rise to a particular, distinct correlative structure. This basic definition allows for a potential reconciliation of the four major attempts at defining race listed in Table 1. Hooton’s essentialist definition, which requires the sharing of characteristics through common descent is clearly compatible with the observation that race is a correlation structure of traits, as is Mayr’s taxonomic definition, which sees races as phenotypically similar groups occupying different ranges. Eco-geographical distinctions between races would be to a degree congruent with respect to genetic and phenotypic traits, so would be expected to yield correlation structures similar to Fig. 1.

There is no reason why such correlation structures could not correspond to Mendelian populations as is required by the population definition of Dobzhansky, nor is there any reason why the distinct correlation structures could not have been subject to historical restrictions in gene flow, as is required by the lineage definition of Templeton. These last two would in point of fact be a prerequisite for the evolution of racial differences in the first instance. The four major race concepts can therefore be united within a common descriptive framework, the differences between them are purely a matter of where the descriptive emphasis is placed.

Section snippets

Races as biological subspecies

Demonstrating the biological construct validity of race does not necessarily address the issue of classification. Although it has been shown that the four major attempts at defining race differ only in terms of qualitative descriptive emphasis, the problem of taxonomic arbitrariness in terms of how diversity within species is classified is still an issue.

An old morphological method for determining the appropriateness of a subspecies classification is the 75% rule, which holds that if 75% of the

Are there multiple extant human species?

A minority of anthropologists in the past have held the view that human racial morphological differences are great enough in some instances to warrant being considered as species level differences [47]; however these views were often based upon the use of scientifically inappropriate morphological comparisons with extant primates (such as degree of prognathism). In this section, the two major definitions of species will be considered in addressing this question.

Overview of findings

There are strong grounds for suggesting that the hypothesis that H. sapiens is polytypic rather than monotypic is at least plausible: this argument is based upon the following lines of reasoning. Firstly, it has been demonstrated that there exists a considerable degree of diversity (as measured by morphology, heterozygosity and FST) within this taxon, which is structured in such a way that is suggestive of the existence of around five major clades (continental populations) corresponding to

Conflicts of interest statement

None declared.

References (70)

  • D. Curnoe et al.

    Number of ancestral human species: A molecular perspective

    HOMO

    (2003)
  • B.G. Charlton

    The James Watson affair

    Med Hypotheses

    (2008)
  • A.R. Templeton

    Human races: A genetic and evolutionary perspective

    Am Anthropol

    (1998)
  • W.F. Bodmer et al.

    Genetics, evolution, and man

    (1976)
  • J.C. Long et al.

    Human genetic diversity and the nonexistence of biological races

    Hum Biol

    (2003)
  • E.A. Hooton

    Methods of racial analysis

    Science

    (1926)
  • E. Mayr

    Principles of systematic zoology

    (1969)
  • T. Dobzhansky

    Genetics of the evolutionary process

    (1970)
  • G. Strkalj

    Form and race. Terminological concepts for the study of human variation

    Mankind Q

    (2000)
  • C.W. Mills

    Blackness visible: Essays on philosophy and race

    (1998)
  • V. Sarich et al.

    Race: the reality of human differences

    (2004)
  • L. Leiberman et al.

    Race in biology and anthropology: A study of college texts and professors

    J Res Sci Teach

    (1992)
  • R.C. Lewontin

    The apportionment of human diversity

    Evol Biol

    (1972)
  • C.L. Brace

    On the race concept

    Curr Anthropol

    (1964)
  • C.L. Brace

    A non-racial approach towards the understanding of human diversity

  • A.W.F. Edwards

    Human genetic diversity: Lewontin’s fallacy

    Bioessays

    (2003)
  • D. Amadon

    The seventy-five percent rule for subspecies

    Condor

    (1949)
  • H. Smith et al.

    Subspecies and classification

    Herp Rev

    (1997)
  • S. Wright

    Evolution and the genetics of populations, vol. 4, variability within and among natural populations

    (1979)
  • A.C. Stone et al.

    High levels of Y chromosome nucleotide diversity in the genus Pan

    Proc Natl Acad Sci USA

    (2002)
  • Goodrum J. The race FAQ, http://www.goodrumj.com/RFaqHTML.html; 2002 [accessed...
  • C. Wise et al.

    Comparative nuclear and mitochondrial genome diversity in humans and chimpanzees

    Mol Biol Evol

    (1997)
  • L. Jorde et al.

    Microsatellite diversity and the demographic history of modern humans

    Proc Natl Acad Sci USA

    (1997)
  • A.M. Bowcock et al.

    High resolution of human evolutionary trees with polymorphic microsatellites

    Nature

    (1994)
  • G.E. Reinartz et al.

    Patterns of microsatellite polymorphism in the range-restricted bonobo (Pan paniscus): considerations for interspecific comparison with chimpanzees (P. troglodytes)

    Mol Ecol

    (2000)
  • W.F. Van Hooft et al.

    Microsatellite analysis of genetic diversity in African buffalo (Syncerus caffer) populations throughout Africa

    Mol Ecol

    (2000)
  • O. Uphyrkina et al.

    Phylogenetics, genome diversity and origin of modern leopard, Panthera pardus

    Mol Ecol

    (2001)
  • E. Eizirik et al.

    Phylogeography, population history and conservation genetics of jaguars (Panthera onca, Mammalia, Felidae)

    Mol Ecol

    (2001)
  • M. Culver et al.

    Genomic ancestry of the American puma (Puma concolor)

    J Hered

    (2000)
  • M.K. Schwartz et al.

    DNA reveals high dispersal synchronizing the population dynamics of Canada lynx

    Nature

    (2002)
  • D. Paetkau et al.

    Genetic structure of the world’s polar bear populations

    Mol Ecol

    (1999)
  • D. Paetkau et al.

    Variation in genetic diversity across the range of North American brown bears

    Con Biol

    (1998)
  • L. Waits et al.

    Nuclear DNA microsatellite analysis of genetic diversity and gene flow in the Scandinavian brown bear (Ursus arctos)

    Mol Ecol

    (2000)
  • J. Garcia-Moreno et al.

    Relationships and genetic purity of the endangered Mexican wolf based on analysis of microsatellite loci

    Con Biol

    (1996)
  • D.J. Girman et al.

    Patterns of population subdivision, gene flow and genetic variability in the African wild dog (Lycaon pictus)

    Mol Ecol

    (2001)
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