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.     

Tracing the origins of stocks of the endangered species <Emphasis Type="Italic">Primula sieboldii</Emphasis> using nuclear microsatellites and chloroplast DNA

We examined the origins of cultivated stocks of the endangered species Primula sieboldii at the individual plant level by using an assignment test based on eight microsatellite loci and regional features of chloroplast DNA (cpDNA) variation of wild populations. To confirm that we had sufficient information for estimating the origins of the stocks, we performed an assignment test with 920 genets that we collected from 32 wild populations with known origins. The test assigned 99.6% of the genets to the population from which they had been sampled, confirming the suitability of the method. We then performed the assignment test with 29 cultivated stocks. The alleged origins of 19 were confirmed by microsatellite and cpDNA variations. In contrast, the alleged origins of five were rejected by both markers. Five stocks, which do not have a reference population located within 30 km of their reputed origin, were not assigned to any population. Stocks whose alleged origins were rejected are inappropriate as restoration materials, because their introduction might disturb local gene pools. Six stock haplotypes could not be detected in wild populations. This may suggest the loss of genetic diversity in the wild and the value of stocks as a gene bank. The genetic method used in this study will also be helpful to detect cryptic invasion by nonendemic genotypes or to trace the origins of plants collected for commercial purposes, a threat to many endangered species.     

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.     

Genetic differentiation among sympatric cuckoo host races: males matter

Generalist parasites regularly evolve host-specific races that each specialize on one particular host species. Many host-specific races originate from geographically structured populations where local adaptations to different host species drive the differentiation of distinct races. However, in sympatric populations where several host races coexist, gene flow could potentially disrupt such host-specific adaptations. Here, we analyse genetic differentiation among three sympatrically breeding host races of the brood-parasitic common cuckoo, Cuculus canorus. In this species, host-specific adaptations are assumed to be controlled by females only, possibly via the female-specific W-chromosome, thereby avoiding that gene flow via males disrupts local adaptations. Although males were more likely to have offspring in two different host species (43% versus 7%), they did not have significantly more descendants being raised outside their putative foster species than females (9% versus 2%). We found significant genetic differentiation for both biparentally inherited microsatellite DNA markers and maternally inherited mitochondrial DNA markers. To our knowledge, this is the first study that finds significant genetic differentiation in biparentally inherited markers among cuckoo host-specific races. Our results imply that males also may contribute to the evolution and maintenance of the different races, and hence that the genes responsible for egg phenotype may be found on autosomal chromosomes rather than the female-specific W-chromosome as previously assumed.     

Apportionment of global human genetic diversity based on craniometrics and skin color

A number of analyses of classical genetic markers and DNA polymorphisms have shown that the majority of human genetic diversity exists within local populations (approximately 85%), with much less among local populations (approximately 5%) or between major geographic regions or "races" (approximately 10%). Previous analysis of craniometric variation (Relethford [1994] Am J Phys Anthropol 95:53-62) found that between 11-14% of global diversity exists among geographic regions, with the remaining diversity existing within regions. The methods used in this earlier paper are extended to a hierarchical partitioning of genetic diversity in quantitative traits, allowing for assessment of diversity among regions, among local populations within regions, and within local populations. These methods are applied to global data on craniometric variation (57 traits) and skin color. Multivariate analysis of craniometric variation shows results similar to those obtained from genetic markers and DNA polymorphisms: roughly 13% of the total diversity is among regions, 6% among local populations within regions, and 81% within local populations. This distribution is concordant with neutral genetic markers. Skin color shows the opposite pattern, with 88% of total variation among regions, 3% among local populations within regions, and 9% within local populations, a pattern shaped by natural selection. The apportionment of genetic diversity in skin color is atypical, and cannot be used for purposes of classification. If racial groups are based on skin color, it appears unlikely that other genetic and quantitative traits will show the same patterns of variation.     

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.     

The Status of the Race Concept in Physical Anthropology

There are hereditary differences among human beings. Some of these differences have geographical correlates. Some genetic variants that produce physical or behavioral deficits occur significantly more often in some areas, or in some ethnic groups, than in others. However, none of these facts provides any intellectual support for the race concept, for racial classifications, or for social hierarchies based on ethnic-group membership.
The geographical element of the race concept is important in theory but is widely ignored in practice since it does not conform well to the facts of current human phenotype distribution. Much of the literature on supposed racial differences involves such geographically meaningless exercises as studying differences among "races" by subdividing a sample of North Americans. If races are defined as geographically delimited conspecific populations characterized by distinctive regional phenotypes, then human races do not exist now and have not existed for centuries,     

Microsatellites uncover extraordinary diversity in native American land races and wild populations of cultivated sunflower

The contemporary oilseed sunflower (Helianthus annuus L.) gene pool is a product of multiple breeding and domestication bottlenecks. Despite substantial phenotypic diversity, modest differences in molecular genetic diversity have been uncovered in anciently and recently domesticated sunflowers. The paucity of molecular marker polymorphisms in early analyses led to the hypothesis of a single domestication origin. Phylogenetic analyses were performed on 47 domesticated and wild germplasm accessions using 122 microsatellite loci distributed throughout the sunflower genome. Extraordinary allelic diversity was found in the Native American land races and wild populations, and progressively less allelic diversity was found in germplasm produced by successive cycles of domestication and breeding. Of 1,341 microsatellite alleles, 489 were unique to land races, exotic domesticates and wild populations, whereas only 15 were unique to elite inbred lines. The number of taxon-specific alleles was 35-fold greater among wild populations (26.27) than elite inbred lines (0.75). Microsatellite genotyping uncovered the possibility of multiple domestication origins. Land races domesticated by Native Americans of the southwestern US (Hopi and Havasupai) formed a clade independent of land races domesticated by Native Americans of the Great Plains and eastern US (Arikara and Seneca). Predictably, domestication and breeding have ratcheted genetic diversity down in sunflower. The contemporary oilseed sunflower gene pool, while not imperiled, could profit from an infusion of novel alleles from the reservoir of latent genetic diversity present in wild populations and Native American land races.     

草鱼中国土著群体与欧美日移居群体遗传差异的线粒体序列分析

草鱼是中国的土著鱼类,自20世纪60年代以来已被移居到100多个国家和地区,主要用来控制水草或水产养殖。本研究通过线粒体D-Loop区（764bp)和COII＋tRNA基因(719bp)序列分析,了解草鱼的中国土著群体（长江、珠江、黑龙江）和国外移居群体（匈牙利多瑙河、美国密西西比河、日本利根川河）之间以及各地方群体间的遗传差异。结果表明,中国土著草鱼群体的遗传变异高于国外移居群体;分子方差分析（AMOVA）表明,不同草鱼群体的遗传变异主要来自群体内,而不同地域间的差异极少;群体两两间Fst值比较表明,大多数群体之间遗传差异极显著;由TCS构建的单倍型网络结构图显示,长江草鱼群体是最原始的群体,其他水系草鱼均由长江群体演化而来;通过基因流分析发现,匈牙利多瑙河群体和日本利根川河群体来自长江和黑龙江群体,美国密西西比河群体除引自长江、黑龙江水系外,还有部分引自于珠江水系。     

Can the spread of agriculture in Europe be followed by tracing the spread of the weed Silene latifolia. A RAPD study

On the basis of gene frequency data of three flavone glycosylating genes, populations of the agricultural weed Silene latifolia (Caryophyllaceae) in Europe can be divided into two chemical races: an eastern and a western race. Morphological data also show a clear east-west division. When the two datasets are combined at least nine different geographical races can be distinguished using cluster analysis. Because these observations are hard to explain by selection, it has been proposed that these different races probably originated as a consequence of migration during the spread of agriculture over Europe in the past. To discriminate between selection and genetic drift many more selectively neutral easy-to-score characters are needed. In order to test whether random amplified polymorphic DNAs (RAPDs) might be suitable for this purpose, we performed a small-scale RAPD analysis on 16 geographical different populations. Using Jaccard's coefficient of similarity, we calculated genetic distances by pair-wise comparisons of both unique and shared amplification products, and a dendrogram was subsequently constructed using an unweighted pair-group method with arithmetical averages (UPGMA). On the basis of the dendrogram two clusters were discerned that clearly coincide with the aforementioned east-west division in populations. As there has been little or no artificial selection on this weed, its migration routes may be a good reflection of the different geographical routes agriculture has taken. We propose that a phylogenetic analysis of RAPD data of many more populations may provide additional information on the spread of agriculture over Europe.     

侯晨曦：附表1-附表2

本研究基于7个叶绿体DNA片段（cpDNA）和2个核DNA片段（ITS和PZ8）的测序数据,对龙血树柴胡（Bupleurum dracaenoides Huan C.Wang,Z.R.He&H.Sun）8个居群的153个样本进行了遗传多样性和分布式样研究。cpDNA片段分析结果显示：龙血树柴胡在物种水平具有较高的遗传多样性（H_d=0.862;P_i=0.00567）,但居群内遗传多样性低,遗传变异主要存在于居群间,遗传分化显著（F_st=0.959）;而核DNA片段ITS和PZ8的数据分析结果显示,其遗传多样性较低（H_d=0.532,P_i =0.00121和H_d=0.349,P_i=0.00060）,遗传变异主要存在于居群内,居群间仅存在一定程度的遗传分化。中性检验和失配分布分析结果发现龙血树柴胡没有经历过近期种群扩张事件,8个居群的153个样本从遗传成份上可被分为两组。研究结果将为龙血树柴胡的资源保护和发掘提供参考。     

INCIPIENT SPECIATION BY SEXUAL ISOLATION IN DROSOPHILA MELANOGASTER: VARIATION IN MATING PREFERENCE AND CORRELATION BETWEEN SEXES

Genetic divergence for characters pertaining to reproductive isolation is of considerable interest in evolutionary biology. Since most studies concentrate on sibling species (for recent reviews, see Wu et al. 1996), we would like to know how much genetic variation exists between populations that are at an incipient stage of speciation. To answer this question, we have begun measuring variations in mating preference among natural isolates of Drosophila melanogaster, represented by the cosmopolitan and Zimbabwe sexual races. We quantify the variation in mating preference and success in both sexes by using a multiple-choice design and an index that is suited to cases of strong asymmetry in mate choice. Different designs and indices for measuring sexual isolation are also discussed. These sexual traits are entirely genetically determined. Surveying four populations in southern Africa and additional cosmopolitan lines, we observe extensive genetic variation in sexual characters as well as strong correlation between sexes. The populations are highly differentiated and represent various stages of evolution between the African and the cosmopolitan type of sexual behaviors. The genetic variation and correlation for these sexual characters coupled with their geographical pattern have interesting implications for models of speciation by sexual selection.     

松杨栅锈菌遗传多样性初步分析

采用ITS-nrDNA-RELP、测序技术、RAPD(随机扩增多态性DNA)分子标记技术,对我国松杨栅锈菌不同地域的5个生理小种11个菌系进行了遗传多样性分化研究.结果表明,该菌在我国的遗传分化与地理来源相关,可分为西部地理群和北方地理群.西部地理群又可分为高山森林生态型(HMF)和平原生态型(WPL).小种遗传分化不一定与致病性分化一致.t检验表明,各生理小种RAPD遗传多样性指数无明显差异,高山森林小种遗传多样性指数(0.5172)略高于平原小种遗传多样性指数(0.5089).核糖体基因转录间隔区高度保守,不适合该菌种内群体遗传多样性分化研究.     

Insights into genome differentiation: pheromone-binding protein variation and population history in the European corn borer (Ostrinia nubilalis)

Examination of sequence variation at nuclear loci can give insights into population history and gene flow that cannot be derived from other commonly used molecular markers, such as allozymes. Here, we report on sequence variation at a single nuclear locus, the pheromone-binding protein (PBP) locus, in the European corn borer (Ostrinia nubilalis). The European corn borer has been divided into three races in New York State on the basis of differences in pheromone communication and life history. Previous allozyme data have suggested that there is a small but significant amount of genetic differentiation between these races. The PBP does not appear to be involved in the pheromone differences between these races. Examination of variation at the PBP locus in the three races reveals no fixed differences between races despite high levels of polymorphism. There also appears to have been considerable recombination in the history of the pheromone-binding protein alleles. Observation of both recombination between alleles and lack of significant nucleotide or insertion/deletion divergence between races leads us to suggest that these populations are either recently diverged or have continued to exchange genetic material subsequent to divergence in pheromone communication and life history.     

Relationship between heterozygosity and genetic distance in the three major races of man

In pairwise comparisons of gene frequency data from the three major races of man, the single locus measures of the heterozygosity within and the genetic distance between races are shown to be strongly correlated across the loci coding for red cell proteins and enzymes. The intercept of the regression line of genetic distance on heterozygosity in protein enzyme loci is statistically insignificant. These findings suggest that the genetic variability at the enzyme and protein loci in man is probably maintained by a balance of mutation and random genetic drift. At the blood group loci, however, the observed relationship between genetic distance and heterozygosity does not follow the expectation of the neutral mutation hypothesis. These observations are discussed in terms of the changes in probability of identical monomorphism in two populations during the process of gene differentiation.     

Demographic signatures accompanying the evolution of selfing in Leavenworthia alabamica

The evolution of selfing from outcrossing is a common transition, yet little is known about the mutations and selective factors that promote this shift. In the mustard family, single-locus self-incompatibility (SI) enforces outcrossing. In this study, we test whether mutations causing self-compatibility (SC) are linked to the self-incompatibility locus (S-locus) in Leavenworthia alabamica, a species where two selfing races (a2 and a4) co-occur with outcrossing populations. We also infer the ecological circumstances associated with origins of selfing using molecular sequence data. Genealogical reconstruction of the Lal2 locus, the putative ortholog of the SRK locus, showed that both selfing races are fixed for one of two different S-linked Lal2 sequences, whereas outcrossing populations harbor many S-alleles. Hybrid crosses demonstrated that S-linked mutations cause SC in each selfing race. These results strongly suggest two origins of selfing in this species, a result supported by population admixture analysis of 16 microsatellite loci and by a population tree built from eight nuclear loci. One selfing race (a4) shows signs of a severe population bottleneck, suggesting that reproductive assurance might have caused the evolution of selfing in this case. In contrast, the population size of race a2 cannot be distinguished from that of outcrossing populations after correcting for differences in selfing rates. Coalescent-based analyses suggest a relatively old origin of selfing in the a4 race (～150 ka ago), whereas selfing evolved recently in the a2 race (～12-48 ka ago). These results imply that S-locus mutations have triggered two recent shifts to selfing in L. alabamica, but that these transitions are not always associated with a severe population bottleneck, suggesting that factors other than reproductive assurance may play a role in its evolution.     

Dwindling genetic diversity in European ground squirrels?

The European ground squirrel (Spermophilus citellus) is endangered and in decline. Populations are increasingly fragmented, and only a coordinated conservation effort at the European level may guarantee its long-term survival. To obtain a general population genetic picture on a larger geographic scale, we screened 117 individuals from seven local populations in Hungary, Romania, and Austria for allelic variation at eleven microsatellite loci. We found a high (23.4%) proportion of private alleles, and a moderate to somewhat elevated level (15.27%) of partitioning of genetic diversity among populations, compared to that found in many other terrestrial mammals. Genetic variability was significantly higher than in earlier studied Czech populations that are considered genetically depleted, but significantly lower than in undisturbed populations of S. suslicus and S. brunneus, that are similar to the European ground squirrel in their ecological requirements, reproductive biology, and social organization. Genetic diversity was also lower than in most presumably “undisturbed” populations of other Sciurid species. This, together with the observed level and pattern of genetic differentiation among populations, such as no significant increase of genetic differentiation with geographic distance and similar variance of genetic differentiation between populations independent of geographic distance, indicated the prevalence of relatively strong drift effects for all populations. A Bayesian STRUCTURE analysis and a factorial correspondence analysis concordantly revealed a fairly complex genetic composition of local populations, but no major geographic trend in the pattern of the genetic composition. Overall, the results suggest disintegration of local colonies that might earlier have been more connected genetically. The STRUCTURE analysis also suggested anthropogenic translocations among single Hungarian populations. Our data on genetic diversity and its distribution do not object to such conservation measures. Translocation of individuals particularly from nearby populations may increase the chances of survival of small and isolated populations and counteract inbreeding at low densities.     

Is chromosomal speciation occurring in house mice in Tunisia?

Two chromosomal races of house mice are present in Tunisia, one represented by mice carrying the 40-acrocentric standard karyotype and the other by a Robertsonian race (2re = 22) homozygous for nine centric fusions (Rb). A comparative summary on allozyme divergence, geographical distribution and level of reproductive isolation in the Tunisian and European Rb races is presented, to which new data on mitochondrial DNA and morphological divergence are added. The Tunisian 22Rb race revealed unique features not matched by the European chromosomal races, such as a decrease in allozymic variability, a higher level of genetic and morphological differentiation and a mosaic geographical distribution. The mtDNA analysis argued in favour of a local origin of the chromosomal divergence suggesting that the higher level of differentiation between the Tunisian races resulted from the older age of the 22Rb race and/or from a severe botdeneck. The decrease in fertility of chromosomal hybrids between the Tunisian races was compatible with the limited genetic introgression between diem. Furthermore, data on the restricted distribution of hybrid populations suggested that premating reproductive barriers may be evolving. The Tunisian 22Rb race is thus an appropriate model to investigate a chromosomally-mediated speciation event.     

Allozyme variation and racial differentiation in Swedish Carex lepidocarpa s.l. (Cyperaceae)

Two morphological races have previously been recognized within the sedge, Carex lepidocarpa , in Sweden. These largely allopatric races are accorded specific status, as C. lepidocarpa s.s. and C. jemtlandica , in Scandinavian floras. A study of allozyme variation in populations from 80 Swedish sites supports the morphological evidence for racial differentiation within C. lepidocarpa. The two races differ from each other in terms of allele frequencies at polymorphic loci and also show different levels of within-population genetic diversity. Material that is morphologically referable to C. lepidocarpa s.s. is characterized by relatively high levels of allozyme variation, both within and between populations. Carex lepidocarpa s.s. is widespread in southern Sweden. In contrast, material that is morphologically assignable to C. jemtlandica shows low levels of within-population genetic diversity, and there is little differentiation between the geographically separated isolates of C. jemtlandica in northern Sweden and on the Baltic island of Gotland. The high degree of morphological similarity and moderate levels of genetic differentiation between the two races within C. lepidocarpa indicate that it is more appropriate to recognize the races as subspecies than as species. The low levels of genetic variation in C. jemtlandica , both within and between populations, suggest that C. jemtlandica may have arisen from C. lepidocarpa (or a near ancestor of C. lepidocarpa) as a result of population fragmentation and isolation in glacial refugia, or during the process of post-glacial colonization of Scandinavia. Lack of allozyme evidence for extensive hybridization between the two races of C. lepidocarpa , despite their ability to hybridize freely where their ranges overlap at present, supports the suggestion that the two races have had separate post-glacial histories.     

Use of genetic effects and genotype by environmental interactions for the classification of mexican races of maize

To examine the questions of whether the additive and dominance effects present for morphological characters in racial crosses are of sufficient consistency and magnitude to allow such genetic effects to be used for racial classification, we used a diallel experiment among the 25 well-defined Mexican races of maize, which include the ancestral stocks of most commercial and genetic maize types. With such an experiment, genetic effects and genotype by environmental interactions for one or more characters can be used to measure genetic and adaptational or environmental similarity. We used average parental effects (general combining abilities), specific effects, and genotype by environmental effects of 21 characters from the diallel (grown at three locations) to group the Mexican races of maize. The groupings based upon average genetic effects and upon genotype by environmental interactions are more satisfactory than groupings based upon specific effects. The standard errors for genetic distances based upon specific (largely dominance) effects seem to be too high for practical use. Principal components analyses of the same data suggest a similar conclusion.-The groupings based upon average genetic effects are in general agreement with previous studies, with the exception of Maíz Dulce, which is grouped with the Cónicos, rather than being isolated from the other Mexican races of maize.