Race and global patterns of phenotypic variation

Phenotypic traits have been used for centuries for the purpose of racial classification. Developments in quantitative population genetics have allowed global comparison of patterns of phenotypic variation with patterns of variation in classical genetic markers and DNA markers. Human skin color shows a high degree of variation among geographic regions, typical of traits that show extensive natural selection. Even given this high level of geographic differentiation, skin color variation is clinal and is not well described by discrete racial categories. Craniometric traits show a level of among-region differentiation comparable to genetic markers, with high levels of variation within populations as well as a correlation between phenotypic and geographic distance. Craniometric variation is geographically structured, allowing high levels of classification accuracy when comparing crania from different parts of the world. Nonetheless, the boundaries in global variation are not abrupt and do not fit a strict view of the race concept; the number of races and the cutoffs used to define them are arbitrary. The race concept is at best a crude first-order approximation to the geographically structured phenotypic variation in the human species. Am J Phys Anthropol 2009. © 2009 Wiley-Liss, Inc.     

Human Races: A Genetic and Evolutionary Perspective

Race is generally used as a synonym for subspecies , which traditionally is a geographically circumscribed, genetically differentiated population. Sometimes traits show independent patterns of geographical variation such that some combination will distinguish most populations from all others. To avoid making "race" the equivalent of a local population, minimal thresholds of differentiation are imposed. Human "races" are below the thresholds used in other species, so valid traditional subspecies do not exist in humans. A "subspecies" can also be defined as a distinct evolutionary lineage within a species. Genetic surveys and the analyses of DNA haplotype trees show that human "races" are not distinct lineages, and that this is not due to recent admixture; human "races" are not and never were "pure." Instead, human evolution has been and is characterized by many locally differentiated populations coexisting at any given time, but with sufficient genetic contact to make all of humanity a single lineage sharing a common evolutionary fate.     

Genetics and the origin of human races

In the last decades, the concept of human races was considered scientifically unfounded as it was not confirmed by genetic evidence. None of the racial classifications, which strongly differ in the number of races and their composition, reflects actual genetic similarity and genealogy of human populations inferred from variability of classical markers and DNA regions. Moreover, intercontinental ("interracial") variability was shown to be far lower than that within populations: the former constitutes 7 to 10% and the latter, about 85% of the total genetic variation. It is believed that the low level of differentiation of regional population groups contradicts their race status and suggests a recent origin of humans from one ancestral population. The results of studies of various genetic systems are in agreement with last conclusion rejecting the hypothesis of regional continuity. According to this hypothesis, the populations of continents regarded as large races have developed during long evolution from local types of archaic humans, in particular, Neanderthals. Phenotypic similarity of different, sometimes unrelated, populations united into one "race" is explained by strong selection since race-diagnostic traits characterize body surface and thus are directly subjected to the influence of environmental (primarily climatic) factors. It has been recently established that variability of the most important of these traits, body and hair pigmentation, is largely controlled by one locus (MC1R), which accounts for its high evolutionary lability. Other traits used for race identification are also likely to be labile and controlled by major genes. However, the fact that the currently existing race classifications are groundless does not mean that such classifications are impossible in principle. Commonly used argumentation (races do not exist because populations are not genetically separated) does not hold water. A polytypic species is characterized by genetic continuity of allopatric populations rather than the presence of narrow genetic boundaries between them. Borderlines between races are usually conventional and arbitrary. As to intergroup variation in humans, it is indeed low but comparable with that in some other species. There are no obstacles to the development of genetic systematics of human races.     

Genetic differentiation among host-associated Alebra leafhoppers (Hemiptera: Cicadellidae)

The limited importance ascribed to sympatric speciation processes via host race formation is partially due to the few cases of host races that have been reported among host populations. This work sheds light on the taxonomy of Alebra leafhoppers and examines the possible existence of host races among host-associated populations. The species of this genus show varying degrees of host association with deciduous trees and shrubs and, frequently, host populations of uncertain taxonomic status coexist and occasionally become pests. Allozyme electrophoresis of 21 Greek populations including sympatric, local and geographically distant samples collected on 13 different plant species, show that they represent at least five species: A. albostriella Fallén, A. viridis (Rey) (sensu Gillham), A. wahlbergi Boheman and two new species. Of these, one is associated to Quercus frainetto and other is specific to Crataegus spp. Significant genetic differences among sympatric and local host populations were found only in A. albostriella, between populations on Turkey oak, beech and common alder. It is suggested that the last two of these host populations may represent different host races. The results show that both the host plant and geographical distance affect the patterns of differentiation in the genus. The formation of some species seems to have been the result of allopatric speciation events while, for others, their origin can be equally explained either by sympatric or allopatric speciation.     

How race becomes biology: Embodiment of social inequality

The current debate over racial inequalities in health is arguably the most important venue for advancing both scientific and public understanding of race, racism, and human biological variation. In the United States and elsewhere, there are well-defined inequalities between racially defined groups for a range of biological outcomes—cardiovascular disease, diabetes, stroke, certain cancers, low birth weight, preterm delivery, and others. Among biomedical researchers, these patterns are often taken as evidence of fundamental genetic differences between alleged races. However, a growing body of evidence establishes the primacy of social inequalities in the origin and persistence of racial health disparities. Here, I summarize this evidence and argue that the debate over racial inequalities in health presents an opportunity to refine the critique of race in three ways: 1) to reiterate why the race concept is inconsistent with patterns of global human genetic diversity; 2) to refocus attention on the complex, environmental influences on human biology at multiple levels of analysis and across the lifecourse; and 3) to revise the claim that race is a cultural construct and expand research on the sociocultural reality of race and racism. Drawing on recent developments in neighboring disciplines, I present a model for explaining how racial inequality becomes embodied—literally—in the biological well-being of racialized groups and individuals. This model requires a shift in the way we articulate the critique of race as bad biology. Am J Phys Anthropol 2009. © 2009 Wiley-Liss, Inc.     

Theodosius Dobzhansky and the genetic race concept

The use of ‘race’ as a proxy for population structure in the genetic mapping of complex traits has provoked controversy about its legitimacy as a category for biomedical research, given its social and political connotations. The controversy has reignited debates among scientists and philosophers of science about whether there is a legitimate biological concept of race. This paper examines the genetic race concept as it developed historically in the work of Theodosius Dobzhansky from the 1930s to 1950s. Dobzhansky’s definitions of race changed over this time from races as ‘arrays of forms’ or ‘clusters’ in 1933–1939, to races as genetically distinct geographical populations in 1940–1946, to races as genetically distinct ‘Mendelian populations’ in 1947–1955. Dobzhansky responded to nominalist challenges by appealing to the biological reality of race as a process. This response came into tension with the object ontology of race that was implied by Dobzhansky’s increasingly holistic treatment of Mendelian populations, a tension, the paper argues, he failed to appreciate or resolve.     

Electrophoretic and immunological characterization of pollen protein ofZea mays races

Electrophoretic and serological studies with proteins extracted from the pollen of 12 races of maize (Zea mays) have proved valuable in distinguishing among these races. Both sodium dodecyl sulfate-polyacrylamide gel electrophoresis and double immunodffusion (Ouchterlony method) were used to analyze the extracted pollen proteins. Jaccard's similarity coefficient was calculated from the data generated by 2-state scoring of the band patterns obtained in each system. Average linkage cluster analysis of the similarity matrices was used to construct phenograms illustrating the similarity among the extracts. The racial groupings indicated in these pheno grams, when compared with those of several morphological studies, show some general agreement. However, there are differences, the most notable being that Chalqueno appeared the most dissimilar of the races studied and that Dulce showed high similarity to Palomero Toluqueño, rather than being an exceptional race as it is usually considered. The possible bearing of the groupings of the races in these phenograms with respect to genetic lineage and selection of maize is discussed.     

Genetics and the Origin of Human “Races”

In the last decades, the concept of human races was considered scientifically unfounded as it was not confirmed by genetic evidence. None of the racial classifications, which strongly differ in the number of races and their composition, reflects actual genetic similarity and genealogy of human populations inferred from variability of classical markers and DNA regions. Moreover, intercontinental (interracial) variability was shown to be far lower than that within populations: the former constitutes 7 to 10% of the total genetic variation and the latter about 85% of it. It is believed that the low level of differentiation of regional population groups contradicts their race status and suggests a recent origin of humans from one ancestral population. The results of studies of various genetic systems are in agreement with the latter conclusion rejecting the hypothesis of regional continuity. According to this hypothesis, the populations of continents regarded as large races have developed during long evolution from local types of archaic humans, in particular, Neanderthals. Phenotypic similarity of different, sometimes unrelated, populations united into one race is explained by strong selection since race-diagnostic traits characterize body surface and thus are directly subjected to the influence of environmental (primarily climatic) factors. It has been recently established that variability of the most important of these traits, body and hair pigmentation, is largely controlled by one locus (MC1R), which accounts for its high evolutionary lability. Other traits used for race identification are also likely to be labile and controlled by major genes. However, the fact that the currently existing race classifications are groundless does not mean that such classifications are impossible in principle. Commonly used argumentation (races do not exist because populations are not genetically separated) does not hold water. A polytypic species is characterized by genetic continuity of allopatric populations rather than the presence of narrow genetic boundaries between them. Borderlines between races are usually conventional and arbitrary. As to intergroup variation in humans, it is indeed low but comparable with that in a number of other species. There are no obstacles to the development of genetic systematics of human races.     

mtDNA perspective of chromosomal diversification and hybridization in Peters' tent-making bat (Uroderma bilobatum: Phyllostomidae)

We compared sequence variation in the complete mitochondrial cytochrome-b gene with chromosomal and geographical variation for specimens of Peters' tent-making bat (Uroderma bilobatum). Three different chromosomal races have been described in this species: a 2n = 42 race from South America east of the Andes, a 2n = 44 from NW Central America and 2n = 38 from the rest of Central America and NW South America. The deepest nodes in the tree were found within the South American race (42 race), which is consistent with a longer history of this race. Average distance among races ranged from 2.5 to 2.9%, with the highest amount of intraracial variation found within the 2n = 42 race (1.7%), intermediate values within the 2n = 38 race (0.9%) and lowest within the 2n = 44 race (0.5%). Variation among chromosomal races accounted for over 55% of molecular variance, whereas variation among populations within races accounted for 6%. The 2n = 38 and 2n = 44 races hybridize in the coastal lowlands of Honduras, near the Gulf of Fonseca. Introgression between these two races is low (two introgressed individuals in 45 examined). Clinal variation across the hybrid zone for the cytochrome-b of U. bilobatum, is similar to clinal variation reported for chromosomes and isozymes of this species. Mismatch distribution analyses suggests that geographical isolation and karyological changes have interplayed in a synergistic fashion. Fixation of the alternative chromosomal rearrangements in geographical isolation and secondary contact is the most likely mechanism accounting for the hybrid zone between the 2n = 38 and 2n = 44 races. If a molecular clock is assumed, with rates ranging from 2.3 to 5.0% per million years, then isolation between these races occurred within the last million years, implying a relatively recent origin of the extant diversity in Uroderma bilobatum. None the less, the three chromosomal races probably represent three different biological species.     

Chromosome polymorphism and C-banding variation of the brachypterous grasshopper Podisma sapporensis Shir. (Orthoptera, Acrididae) in Hokkaido, northern Japan

The grasshopper Podisma sapporensis consists of two main chromosome races in Hokkaido. The western group of populations of P. sapporensis, belonging to the XO race, has a diploid number of chromosomes 2n = 23 in the male and 2n = 24 in the female (sex determination XO male/XX female). The eastern group of populations of this species, belonging to the XY race, differs from the western one as a result of Robertsonian translocation between the originally acrocentric X chromosome and M5 autosome in homozygous state, having resulted in the forming of chromosome sex determination neo-XY male/neo-XX female (2n = 22). These races are geographically isolated by the mountainous system consisting of the Mts Daisetsu and Hidaka range, occupying the central part of the island. The hybrid zones between the races have not so far been discovered. Various levels of polymorphism for the pericentric inversions and C-banding variation exist in different chromosomes throughout populations in both chromosome races. In some solitary populations (the population at the summit of Mt Yotei, populations in the vicinity of Naganuma, Oketo, and Tanno) pericentric inversions are fixed in some pairs of chromosomes, which enables marking of the discrete karyomorphes. In the Mt Daisengen population all chromosomes are two-armed as a result of fixing the pericentric inversions. These facts contradict karyotypical conservatism of the tribe Podismini. The level of diversity of P. sapporensis karyotypes could provide a new perspective on the evolutionary process of different karyotype in Orthoptera. The considerable occurrence of polymorphism in chromosomes suggests that karyotypic diversification is undergoing in P. sapporensis. The authors also proposed that P. sapporensis would be divided into four chromosome subraces in the XO chromosome race and two chromosome subraces in the XY race, on the basis of karyotypic features. These races may have been established by fundamental climatic changes during the glacial epoch.     

On the reality of local and ecological races in lymnaeid snails (Mollusca,Gastropoda, Lymnaeidae)

The reality of ecological and local races was investigated in two widespread Palearctic species of lymnaeid snails (Lymnaea stagnalis and Radix auricularia). Several methods of statistical analysis were used, including two-way ANOVA, cluster analysis, and discriminant analysis for six plastic shell characters. It was shown that none of the methods used could convincingly demonstrate that ecological and local races were present in the studied species. Even in cases when statistically significant differences among the populations in the morphology of shells were revealed, these differences were very small and did not correspond to the meaning that was put into the concept of “race” by malacologists in the past. Perhaps, the formation of such races in pond snails is possible only in case of populations being formed in suboptimal conditions, for example, in thermal springs or at large depths. This being the case, the distinguishing of races requires using other shell characters, both quantitative and qualitative ones.     

Flavonoid races in lasthenia (Compositae)

Nine of the 13 taxa ofLasthenia in which two or more populations were examined for flavonoid constituents exhibited interpopulation variation in these constituents. In certain species entire classes of compounds were present in some races and absent from others. Some of these biochemical differences are due to the failure of certain steps to occur in the biosynthesis of various flavonoids from precursor compounds. Another pattern of variation involves intraspecific differences in the nature of flavonoid glycosides that are produced. In view of the close biosynthetic relationships among all the flavonoids produced byLasthenia, the genetic differences among the flavonoid races of a species may be small. Whether or not these biochemical differences have any adaptive significance is problematical at present.     

The races of maize: III. choices of appropriate characters for racial classification

Analyses of variance for 111 characters from 55 races and subraces of maize from eastern South America grown at Piracicaba, S. P., Brazil, between 1960 and 1965, indicated that those characters which were least affected by environmental factors and interactions were reproductive characters. In particular, the component of variance due to differences among races for certain ear and kernel characters was greater than the sum of the corresponding components due to differences among years and race by year interactions. The converse was true for all vegetative characters. Tassel characters tended to be intermediate between ear and plant characters. While some indices had larger components of variance attributable to racial differences than to the effects of environment and/or environmental interaction, some commonly used ones, such as cob/rachis and rachilla/kernel indices, proved to be quite susceptible to environmental influences. Again, indices based upon solely vegetative characters were consistently influenced more strongly by environmental factors and interaction than were those based on reproductive characters.     

Biological races in humans

Races may exist in humans in a cultural sense, but biological concepts of race are needed to access their reality in a non-species-specific manner and to see if cultural categories correspond to biological categories within humans. Modern biological concepts of race can be implemented objectively with molecular genetic data through hypothesis-testing. Genetic data sets are used to see if biological races exist in humans and in our closest evolutionary relative, the chimpanzee. Using the two most commonly used biological concepts of race, chimpanzees are indeed subdivided into races but humans are not. Adaptive traits, such as skin color, have frequently been used to define races in humans, but such adaptive traits reflect the underlying environmental factor to which they are adaptive and not overall genetic differentiation, and different adaptive traits define discordant groups. There are no objective criteria for choosing one adaptive trait over another to define race. As a consequence, adaptive traits do not define races in humans. Much of the recent scientific literature on human evolution portrays human populations as separate branches on an evolutionary tree. A tree-like structure among humans has been falsified whenever tested, so this practice is scientifically indefensible. It is also socially irresponsible as these pictorial representations of human evolution have more impact on the general public than nuanced phrases in the text of a scientific paper. Humans have much genetic diversity, but the vast majority of this diversity reflects individual uniqueness and not race.     

Microsatellite characterization of Andean races of common bean (<Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> L.)

The Andean gene pool of common bean (Phaseolus vulgaris L.) has high levels of morphological diversity in terms of seed color and size, growth habit and agro-ecological adaptation, but previously was characterized by low levels of molecular marker diversity. Three races have been described within the Andean gene pool: Chile, Nueva Granada and Peru. The objective of this study was to characterize a collection of 123 genotypes representing Andean bean diversity with 33 microsatellite markers that have been useful for characterizing race structure in common beans. The genotypes were from both the primary center of origin as well as secondary centers of diversity to which Andean beans spread and represented all three races of the gene pool. In addition we evaluated a collection of landraces from Colombia to determine if the Nueva Granada and Peru races could be distinguished in genotypes from the northern range of the primary center. Multiple correspondence analyses of the Andean race representatives identified two predominant groups corresponding to the Nueva Granada and Peru races. Some of the Chile race representatives formed a separate group but several that had been defined previously as from this race grouped with the other races. Gene flow was more notable between Nueva Granada and Peru races than between these races and the Chile race. Among the Colombian genotypes, the Nueva Granada and Peru races were identified and introgression between these two races was especially notable. The genetic diversity within the Colombian genotypes was high, reaffirming the importance of this region as an important source of germplasm. Results of this study suggest that the morphological classification of all climbing beans as Peru race genotypes and all bush beans as Nueva Granada race genotypes is erroneous and that growth habit traits have been mixed in both races, requiring a re-adjustment in the concept of morphological races in Andean beans.     

The Structure, Distribution and Evolution of the Ta1 Retrotransposable Element Family of Arabidopsis Thaliana

The Ta1 elements are a low copy number, copia-like retrotransposable element family of Arabidopsis thaliana. Six Ta1 insertions comprise all of the Ta1 element copies found in three geographically diverse A. thaliana races. These six elements occupy three distinct target sites: Ta1-1 is located on chromosome 5 and is common to all three races (Col-0, Kas-1 and La-0). Ta1-2 is present in two races on chromosome 4 (Kas-1 and La-0), and Ta1-3, also located on chromosome 4, is present only in one race (La-0). The six Ta1 insertions share >96% nucleotide identity, yet are likely to be incapable of further transposition due to deletions or nucleotide changes that alter either the coding capacity of the elements or conserved protein domains required for retrotransposition. Nucleotide sequence comparisons of these elements and the distribution of Ta1 among 12 additional A. thaliana geographical races suggest that Ta1-1 predated the global dispersal of A. thaliana. As the species spread throughout the world, two additional transposition events occurred which gave rise first to Ta1-2 and finally to Ta1-3.     

Nucleolar organizing chromosomes ofRicinus

Summary Pachytene chromosome morphology was compared in nine races ofRicinus communis L. (2n = 20), using pollen mother cells (PMCs) and light microscopy. Of the ten bivalents, only the two possessing nucleolar organizing regions (NORs), chromosomes 2 and 7, exhibit structural variations among the races. The NORs are located in the short arms of these two chromosomes. Most of the observed structural variations affect these short arms, which are similar morphologically and consist largely of heterochromatic segments. The PMCs contain a single nucleolus and this is associated with the NOR of each of the two chromosomes at a particular frequency in each race. In eight races, a nucleolar constriction (NC) is present in either chromosome 2 or chromosome 7. In these races, the nucleolus is associated with the chromosome possessing an NC at a frequency of 100% and with the chromosome lacking an NC at a frequency ranging between 5.6 and 100%, depending upon the race. No microscopically visible NC is present in the ninth race. In this race, the nucleolus is associated with both chromosomes 2 and 7 at a frequency of 100%. The association of the nucleolus with a chromosome possessing an NC is at the NC and with a chromosome lacking an NC is at the terminal heterochromatic segment of the short arm. Several interpretations are offered to account for the variations in frequency of association between the nucleolus and each of the nucleolar organizing chromosomes. It is suggested that the two non-linked NORs have evolved through some intragenomic changes rather than polyploidy, that this species is highly intolerant to structural variations other than those occurring in or near the NORs, and that structural variations in the nucleolar organizing chromosomes are not associated with racial variations in plant phenotype.Paper of the Journal Series, New Jersey Agricultural Experiment Station     

No apparent reduction of gene flow in a hybrid zone between the West and North European karyotypic groups of the common shrew, Sorex araneus

The common shrew, Sorex araneus, exhibits an unusually high level of karyotypic variation. Populations with identical or similar karyotypes are defined as chromosome races, which are, in turn, grouped into larger evolutionary units, karyotypic groups. Using six microsatellite markers, we investigated the genetic structure of a hybrid zone between the Sidensjö and Abisko chromosome races, representatives of two distinct karyotypic groups believed to have been separated during the last glacial maximum, the West European karyotypic group (western group) and the North European karyotypic group (northern group), respectively. Significant F_ST values among populations suggest some weak genetic structure. All hierarchical levels show similar levels of genetic differentiation, equivalent to levels of genetic structure in several intraracial studies of common shrew populations from central Europe. Notably, genetic differentiation was of the same order of magnitude between and within karyotypic groups. Although the genetic differentiation was weak, the correlation between genetic and geographical distance was positive and significant, suggesting that the genetic variation observed between populations is a function of geographical distance rather than racial origin. Hence, considerable chromosomal differences do not seem to prevent extensive gene flow.     

Apportionment of racial diversity: A review

It has become increasingly popular to theorize and assert significant genetic differences between arbitrary regional, ethnic, and racial groupings of humans. Beginning with Livingstone, Brace, and Newman is the early 1960s, biological anthropologists have shown that variation in human traits is non‐concordant along racial lines, as they are products of overlapping, dynamic selective pressures. In 1972, Lewontin analyzed blood groups, serum protein, and red blood cell enzyme variants and found that only about 6% of total genetic variance was accounted for by race, while the majority of variance is accounted for by differences between individuals. Using similar assays, Latter obtained similar results in 1980. In 1982, Nei and Roychoudhury analyzed 62 protein variants and 23 blood groups, finding that roughly 10% of genetic variance was accounted for by race. Analyzing protein, blood group, and HLA variants, Ryman and coworkers obtained similar figures in 1983. More recently, Dean and coworkers (1994) and Barbujani and coworkers (1997) have used PCR techniques to analyze RFLP and microsattelite loci, again yielding estimates of around 10% for the amount of genetic variance accounted for by race. Furthermore, recent research on regional and racial variance in mtDNA (Excoffier and coworkers, 1992), a traditional marker for human racial groupings, shows a higher proportion of variance within than across racial categories. These studies used a variety of assays and analytical techniques, some of which are designed to maximize the amount of variance accounted for by race. In light of this, the low proportion of genetic variance across racial groupings strongly suggests a re‐examination of the race concept. It no longer makes sense to adhere to arbitrary racial categories, or to expect that the next genetic study will provide the key to racial classification. Evol. Anthropol. 10:34–40, 2001. © 2001 Wiley‐Liss, Inc.