Human genetic diversity: Lewontin’s fallacy
In popular articles that play down the genetical differences among human populations, it is often stated that about 85% of the total genetical variation is due to individual differences within populations and only 15% to differences between populations or ethnic groups. It has therefore been proposed that the division of Homo sapiens into these groups is not justified by the genetic data. This conclusion, due to R.C. Lewontin in 1972, is unwarranted because the argument ignores the fact that most of the information that distinguishes populations is hidden in the correlation structure of the data and not simply in the variation of the individual factors. The underlying logic, which was discussed in the early years of the last century, is here discussed using a simple genetical example.
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Is the Concept of Race Illegitimate?
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The many species of humanity
Naming new human species may seem to be a harmless endeavor, of little interest to all but a few specialists playing out the consequences of different evolutionary explanations of phyletic variation, but it has significant implications in how humanity is viewed because studies of race and human evolution are inexorably linked. When essentialist approaches are used to interpret variation in the past as taxonomic rather than populational, as increasingly has been the case, it serves to underscore a typological view of modern human variation. In terms of how they are treated in analysis, there often seems to be no difference between the species, subspecies, or paleodemes of the past and the populations or races whose interrelationships and demographic history are discussed today. This is not inconsequential because both history and current practice shows that science, especially anthropology, is not isolated from society.
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Deconstructing the relationship between genetics and race
The success of many strategies for finding genetic variants that underlie complex traits depends on how genetic variation is distributed among human populations. This realization has intensified the investigation of genetic differences among groups, which are often defined by commonly used racial labels. Some scientists argue that race is an adequate proxy of ancestry, whereas others claim that race belies how genetic variation is apportioned. Resolving this controversy depends on understanding the complicated relationship between race, ancestry and the demographic history of humans. Recent discoveries are helping us to deconstruct this relationship, and provide better guidance to scientists and policy makers.
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Evidence for Gradients of Human Genetic Diversity Within and Among Continents
Genetic variation in humans is sometimes described as being discontinuous among continents or among groups of individuals, and by some this has been interpreted as genetic support for "races." A recent study in which >350 microsatellites were studied in a global sample of humans showed that they could be grouped according to their continental origin, and this was widely interpreted as evidence for a discrete distribution of human genetic diversity. Here, we investigate how study design can influence such conclusions. Our results show that when individuals are sampled homogeneously from around the globe, the pattern seen is one of gradients of allele frequencies that extend over the entire world, rather than discrete clusters. Therefore, there is no reason to assume that major genetic discontinuities exist between different continents or "races."
PDF file
In popular articles that play down the genetical differences among human populations, it is often stated that about 85% of the total genetical variation is due to individual differences within populations and only 15% to differences between populations or ethnic groups. It has therefore been proposed that the division of Homo sapiens into these groups is not justified by the genetic data. This conclusion, due to R.C. Lewontin in 1972, is unwarranted because the argument ignores the fact that most of the information that distinguishes populations is hidden in the correlation structure of the data and not simply in the variation of the individual factors. The underlying logic, which was discussed in the early years of the last century, is here discussed using a simple genetical example.
PDF file
Is the Concept of Race Illegitimate?
PDF file
The many species of humanity
Naming new human species may seem to be a harmless endeavor, of little interest to all but a few specialists playing out the consequences of different evolutionary explanations of phyletic variation, but it has significant implications in how humanity is viewed because studies of race and human evolution are inexorably linked. When essentialist approaches are used to interpret variation in the past as taxonomic rather than populational, as increasingly has been the case, it serves to underscore a typological view of modern human variation. In terms of how they are treated in analysis, there often seems to be no difference between the species, subspecies, or paleodemes of the past and the populations or races whose interrelationships and demographic history are discussed today. This is not inconsequential because both history and current practice shows that science, especially anthropology, is not isolated from society.
PDF file
Deconstructing the relationship between genetics and race
The success of many strategies for finding genetic variants that underlie complex traits depends on how genetic variation is distributed among human populations. This realization has intensified the investigation of genetic differences among groups, which are often defined by commonly used racial labels. Some scientists argue that race is an adequate proxy of ancestry, whereas others claim that race belies how genetic variation is apportioned. Resolving this controversy depends on understanding the complicated relationship between race, ancestry and the demographic history of humans. Recent discoveries are helping us to deconstruct this relationship, and provide better guidance to scientists and policy makers.
PDF file
Evidence for Gradients of Human Genetic Diversity Within and Among Continents
Genetic variation in humans is sometimes described as being discontinuous among continents or among groups of individuals, and by some this has been interpreted as genetic support for "races." A recent study in which >350 microsatellites were studied in a global sample of humans showed that they could be grouped according to their continental origin, and this was widely interpreted as evidence for a discrete distribution of human genetic diversity. Here, we investigate how study design can influence such conclusions. Our results show that when individuals are sampled homogeneously from around the globe, the pattern seen is one of gradients of allele frequencies that extend over the entire world, rather than discrete clusters. Therefore, there is no reason to assume that major genetic discontinuities exist between different continents or "races."
PDF file
