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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 000:000000 (2009) The global pattern of gene identity variation reveals a history of long-range migrations, bottlenecks, and local mate exchange: Implications for biological race
From the full text:
The Sub-Saharan African results have important implications for race. For Sub-Saharan Africans to belong to a single race, all Sub-Saharan African populations would have to cluster together on a single branch of a larger species tree, which means that each population would have about the same level of gene identity with all non-Sub-Saharan African populations, i.e., the individual population strata in Figure 3D wouldnt exist. These separate population strata indicate that the Sub- Saharan African populations do not cluster together, and, therefore, that there is no Sub-Saharan African race in any taxonomic sense.
If the independent regions model was correct, then individuals in the same geographic region would on average be more closely related to each other genetically than would be individuals in different geographic regions. Even in this case, the problem of finding a threshold level of gene identity for declaring taxonomic significance would remain unsolved.
In reality, the between-population gene identity pattern is nested. Because the between-population pattern is nested in Sub-Saharan Africa, and because Sub- Saharan African populations straddle the root of the species- wide population tree (e.g., Li et al., 2008), there can be no Sub-Saharan African race under the shared genetic relationship criterion. The first division in the population hierarchy that coincides with continental locations separates non-African populations from African populations. This division is consistent with the existence of a non-African race, but because of the root, the Africans would still not constitute a race. Another major division along continental lines separates East Asian and Native American populations from all others. However, classifiers would need to put East Asians and Native Americans into a sub-race, because they would already be members of the non-African race. Thus, we see that nested pattern of variation would require that the geographic groups that anthropologists traditionally considered races could not be assigned to the same level of hierarchical classification.
AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 000:000000 (2009) Human DNA Sequences: More Variation and Less Race Jeffrey C. Long,1* Jie Li,1 and Meghan E. Healy2
We now turn to how these estimates and analyses of genetic diversity within and between populations effect the assessment of human races in our species. Lewontins argument against race is historically important and interesting (Lewontin, 1972). He was not the first to argue against race taxonomy using genetics, but his argument was unique. He confronted race by trying to show that classical racial groupings account for too little of the total diversity to be worth further concern. Our results show that race, as represented in the TLIM, fits both data sets poorly. Comparisons between raw and model-generated diversity and genetic distance estimates reveal that the TLIM indeed misrepresents both the pattern and amount of diversity within and between populations. A strong message from our findings is that the model used in an analysis biases the outcome measurements. We agree entirely with Lewontin that classical race taxonomy is a poor reflection of human diversity. However, we do not believe that the diversity components that he estimated using this model reflect an intrinsic property of human genetic structure as some scientists have suggested (Templeton, 1999, 2007; Brown and Armelagos, 2001).
The pattern of DNA sequence diversity also creates some unsettling problems for applying to humans the definition of races as groups of populations within which the individuals are more related to each other than they are to members of other such groups (Hartl and Clark, 1997). This definition essentially encompasses Templetons evolutionary lineage definition of race (Templeton, 1999) and Dobzhanskys gene frequency definition of race (Dobzhansky, 1970). Although it is logically consistent to group populations by relationship, the nested pattern of genetic diversity in the EHM disagrees with the traditional anthropological classifications that placed continental populations at the same level of classification (i.e., race). A classification that takes into account evolutionary relationships and the nested pattern of diversity would require that Sub-Saharan Africans are not a race because the most exclusive group that includes all Sub- Saharan African populations also includes every non- Sub-Saharan African population (Figs. 2B and 4B). Moreover, the Out-of-Africa branch would place all Eurasians in the same race, but this would necessitate placing Europeans and Asians in sub-races. Several sub-sub-races would be necessary to account for the population groups throughout the world. We see no need for such a classification in light of the fact that our evolutionary history gives good guidance for understanding the structure of human diversity.
Some biologists define races based purely on correct assignment of individuals to groups. The best known version of this approach is the seventy-five percent correct classification rule (Amadon, 1949; Mayr, 1969). Edwards has explained how accurate classification will be achieved when multiple polymorphic loci are considered (Edwards, 2003), and we see empirically that there are applications to human data that satisfy the seventyfive percent criterion (Rosenberg et al., 2002; Bamshad et al., 2003). However, the clustering methods in popular use produce human population groups that have a simpler structure than even the TLIM (Pritchard et al., 2000; Falush et al., 2003). This structure is clearly a weak description of the true human population structure, because it does not capture the complete nested arrangement of populations. We do not expect that such a classification will serve any application better than the full nested structure of populations.
In summary, we find for our own data and for a large published data set, that human populations have much diversity when DNA sequences are considered. We show that simple partitions of diversity are biased and that they hide the true extent of diversity. The pattern of diversity that we reveal is richer and worthy of study as it sheds light on the peopling of the world, ancestry and natural selection, and disease patterns (Ramachandran et al., 2005; Rosenberg et al., 2005; Lohmueller et al., 2008).
AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 000:000000 (2009) RACE AND GLOBAL PATTERNS OF PHENOTYPIC VARIATION
Does the global pattern of phenotypic variation seen in skin color and craniometric traits support the idea of race? The answer depends on initial definitions and use of the term race. On the one hand, the idea of discrete races in the typological mindset of past centuries clearly does not apply to humans (Templeton, 1998; Graves, 2001). There is, however, geographic patterning to human biological variation, both for traits affected strongly by natural selection, such as skin color, and for traits whose distribution tends, on average, to be more neutral, such as craniometrics and many genetic polymorphisms. I suggest that typical uses of the concept of geographic race today are simply crude labels imposed upon this geographically structured variation. In that sense, race is culturally constructed, as all labels are, but it is also based on an underlying reality of biological variation. Rather than argue about whether race is a cultural construct (an idea that many unfortunately take as being equivalent to a denial of variation) or that race is real, it might be more useful to consider race as a culturally constructed label that crudely and imprecisely describes real variation.....
The final question is one of semantics. In cases where broad geographic groups are used, should we refer to these groups as races or should we use more politically correct terms such as geographic regions or geographic clusters? On the one hand, the very concept of race has such historical baggage that continued use of the term tends to reify incorrect conceptions of human variation. On the other hand, it is probably naıve to think that the term can be wiped from everyday use and misuse. It might be more appropriate to answer the questions about race by noting that race is a crude first order approximation to human biological variation that is arbitrary in terms of the number and definition of races. As such, race may not provide the best way of describing or analyzing human variation.
AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 000:000000 (2009) The global pattern of gene identity variation reveals a history of long-range migrations, bottlenecks, and local mate exchange: Implications for biological race
From the full text:
The Sub-Saharan African results have important implications for race. For Sub-Saharan Africans to belong to a single race, all Sub-Saharan African populations would have to cluster together on a single branch of a larger species tree, which means that each population would have about the same level of gene identity with all non-Sub-Saharan African populations, i.e., the individual population strata in Figure 3D wouldnt exist. These separate population strata indicate that the Sub- Saharan African populations do not cluster together, and, therefore, that there is no Sub-Saharan African race in any taxonomic sense.
If the independent regions model was correct, then individuals in the same geographic region would on average be more closely related to each other genetically than would be individuals in different geographic regions. Even in this case, the problem of finding a threshold level of gene identity for declaring taxonomic significance would remain unsolved.
In reality, the between-population gene identity pattern is nested. Because the between-population pattern is nested in Sub-Saharan Africa, and because Sub- Saharan African populations straddle the root of the species- wide population tree (e.g., Li et al., 2008), there can be no Sub-Saharan African race under the shared genetic relationship criterion. The first division in the population hierarchy that coincides with continental locations separates non-African populations from African populations. This division is consistent with the existence of a non-African race, but because of the root, the Africans would still not constitute a race. Another major division along continental lines separates East Asian and Native American populations from all others. However, classifiers would need to put East Asians and Native Americans into a sub-race, because they would already be members of the non-African race. Thus, we see that nested pattern of variation would require that the geographic groups that anthropologists traditionally considered races could not be assigned to the same level of hierarchical classification.
AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 000:000000 (2009) Human DNA Sequences: More Variation and Less Race Jeffrey C. Long,1* Jie Li,1 and Meghan E. Healy2
We now turn to how these estimates and analyses of genetic diversity within and between populations effect the assessment of human races in our species. Lewontins argument against race is historically important and interesting (Lewontin, 1972). He was not the first to argue against race taxonomy using genetics, but his argument was unique. He confronted race by trying to show that classical racial groupings account for too little of the total diversity to be worth further concern. Our results show that race, as represented in the TLIM, fits both data sets poorly. Comparisons between raw and model-generated diversity and genetic distance estimates reveal that the TLIM indeed misrepresents both the pattern and amount of diversity within and between populations. A strong message from our findings is that the model used in an analysis biases the outcome measurements. We agree entirely with Lewontin that classical race taxonomy is a poor reflection of human diversity. However, we do not believe that the diversity components that he estimated using this model reflect an intrinsic property of human genetic structure as some scientists have suggested (Templeton, 1999, 2007; Brown and Armelagos, 2001).
The pattern of DNA sequence diversity also creates some unsettling problems for applying to humans the definition of races as groups of populations within which the individuals are more related to each other than they are to members of other such groups (Hartl and Clark, 1997). This definition essentially encompasses Templetons evolutionary lineage definition of race (Templeton, 1999) and Dobzhanskys gene frequency definition of race (Dobzhansky, 1970). Although it is logically consistent to group populations by relationship, the nested pattern of genetic diversity in the EHM disagrees with the traditional anthropological classifications that placed continental populations at the same level of classification (i.e., race). A classification that takes into account evolutionary relationships and the nested pattern of diversity would require that Sub-Saharan Africans are not a race because the most exclusive group that includes all Sub- Saharan African populations also includes every non- Sub-Saharan African population (Figs. 2B and 4B). Moreover, the Out-of-Africa branch would place all Eurasians in the same race, but this would necessitate placing Europeans and Asians in sub-races. Several sub-sub-races would be necessary to account for the population groups throughout the world. We see no need for such a classification in light of the fact that our evolutionary history gives good guidance for understanding the structure of human diversity.
Some biologists define races based purely on correct assignment of individuals to groups. The best known version of this approach is the seventy-five percent correct classification rule (Amadon, 1949; Mayr, 1969). Edwards has explained how accurate classification will be achieved when multiple polymorphic loci are considered (Edwards, 2003), and we see empirically that there are applications to human data that satisfy the seventyfive percent criterion (Rosenberg et al., 2002; Bamshad et al., 2003). However, the clustering methods in popular use produce human population groups that have a simpler structure than even the TLIM (Pritchard et al., 2000; Falush et al., 2003). This structure is clearly a weak description of the true human population structure, because it does not capture the complete nested arrangement of populations. We do not expect that such a classification will serve any application better than the full nested structure of populations.
In summary, we find for our own data and for a large published data set, that human populations have much diversity when DNA sequences are considered. We show that simple partitions of diversity are biased and that they hide the true extent of diversity. The pattern of diversity that we reveal is richer and worthy of study as it sheds light on the peopling of the world, ancestry and natural selection, and disease patterns (Ramachandran et al., 2005; Rosenberg et al., 2005; Lohmueller et al., 2008).
AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 000:000000 (2009) RACE AND GLOBAL PATTERNS OF PHENOTYPIC VARIATION
Does the global pattern of phenotypic variation seen in skin color and craniometric traits support the idea of race? The answer depends on initial definitions and use of the term race. On the one hand, the idea of discrete races in the typological mindset of past centuries clearly does not apply to humans (Templeton, 1998; Graves, 2001). There is, however, geographic patterning to human biological variation, both for traits affected strongly by natural selection, such as skin color, and for traits whose distribution tends, on average, to be more neutral, such as craniometrics and many genetic polymorphisms. I suggest that typical uses of the concept of geographic race today are simply crude labels imposed upon this geographically structured variation. In that sense, race is culturally constructed, as all labels are, but it is also based on an underlying reality of biological variation. Rather than argue about whether race is a cultural construct (an idea that many unfortunately take as being equivalent to a denial of variation) or that race is real, it might be more useful to consider race as a culturally constructed label that crudely and imprecisely describes real variation.....
The final question is one of semantics. In cases where broad geographic groups are used, should we refer to these groups as races or should we use more politically correct terms such as geographic regions or geographic clusters? On the one hand, the very concept of race has such historical baggage that continued use of the term tends to reify incorrect conceptions of human variation. On the other hand, it is probably naıve to think that the term can be wiped from everyday use and misuse. It might be more appropriate to answer the questions about race by noting that race is a crude first order approximation to human biological variation that is arbitrary in terms of the number and definition of races. As such, race may not provide the best way of describing or analyzing human variation.
