Researchers have investigated the relationship between race and genetics as part of efforts to understand how biology may or may not contribute to human racial categorization. Today, the consensus among scientists is that race is a social construct, and that using it as a proxy for genetic differences among populations is misleading.
Many constructions of race are associated with phenotypical traits and geographic ancestry, and scholars like Carl Linnaeus have proposed scientific models for the organization of race since at least the 18th century. Following the discovery of Mendelian genetics and the mapping of the human genome, questions about the biology of race have often been framed in terms of genetics. A wide range of research methods have been employed to examine patterns of human variation and their relations to ancestry and racial groups, including studies of individual traits, studies of large populations and genetic clusters, and studies of genetic risk factors for disease.
Research into race and genetics has also been criticized as emerging from, or contributing to, scientific racism. Genetic studies of traits and populations have been used to justify social inequalities associated with race, despite the fact that patterns of human variation have been shown to be mostly clinal, with human genetic code being approximately 99.6% – 99.9% identical between individuals and without clear boundaries between groups.
Some researchers have argued that race can act as a proxy for genetic ancestry because individuals of the same racial category may share a common ancestry, but this view has fallen increasingly out of favor among experts. The mainstream view is that it is necessary to distinguish between biology and the social, political, cultural, and economic factors that contribute to conceptions of race.
Phenotype may have a tangential connection to DNA, but it is still only a rough proxy that would omit various other genetic information. Today, in a somewhat similar way that "gender" is differentiated from the more clear "biological sex", scientists state that potentially "race" / phenotype can be differentiated from the more clear "ancestry". However, this system has also still come under scrutiny as it may fall into the same problems – which would be large, vague groupings with little genetic value.
Overview The concept of race
The concept of "race" as a classification system of humans based on visible physical characteristics emerged over the last five centuries, influenced by European colonialism. However, there is widespread evidence of what would be described in modern terms as racial consciousness throughout the entirety of recorded history. For example, in Ancient Egypt there were four broad racial divisions of human beings: Egyptians, Asiatics, Libyans, and Nubians. The concept has manifested in different forms based on social conditions of a particular group, often used to justify unequal treatment. Early influential attempts to classify humans into discrete races include 4 races in Carl Linnaeus's Systema Naturae (Homo europaeus, asiaticus, americanus, and afer) and 5 races in Johann Friedrich Blumenbach's On the Natural Variety of Mankind. Notably, over the next centuries, scholars argued for anywhere from 3 to more than 60 race categories. Race concepts have changed within a society over time; for example, in the United States social and legal designations of "White" have been inconsistently applied to Native Americans, Arab Americans, and Asian Americans, among other groups (See main article: Definitions of whiteness in the United States). Race categories also vary worldwide; for example, the same person might be perceived as belonging to a different category in the United States versus Brazil. Because of the arbitrariness inherent in the concept of race, it is difficult to relate it to biology in a straightforward way.
Race and human genetic variation There is broad consensus across the biological and social sciences that race is a social construct, not an accurate representation of human genetic variation. As more progress has been made on sequencing the human genome, it has been found that any two humans will share an average of 99.35% of their DNA based on the approximately 3.1 billion haploid base pairs. However, this number should be understood as an average, any two specific individuals can have their genomes differ by more or less than 0.65%. Additionally, this average is an estimate, subject to change as additional sequences are discovered and populations sampled. In 2010, the genome of Craig Venter was found to differ by an estimated 1.59% from a reference genome created by the National Center for Biotechnology Information.
We nonetheless see wide individual variation in phenotype, which arises from both genetic differences and complex gene-environment interactions. The vast majority of this genetic variation occurs within groups; very little genetic variation differentiates between groups. Crucially, the between-group genetic differences that do exist do not map onto socially recognized categories of race. Furthermore, although human populations show some genetic clustering across geographic space, human genetic variation is "clinal", or continuous. This, in addition to the fact that different traits vary on different clines, makes it impossible to draw discrete genetic boundaries around human groups. Finally, insights from ancient DNA are revealing that no human population is "pure" – all populations represent a long history of migration and mixing.
Sources of human genetic variation Genetic variation arises from mutations, from natural selection, migration between populations (gene flow) and from the reshuffling of genes through sexual reproduction. Mutations lead to a change in the DNA structure, as the order of the bases are rearranged. Resultantly, different polypeptide proteins are coded. Some mutations may be positive and can help the individual survive more effectively in their environment. Mutation is counteracted by natural selection and by genetic drift; note too the founder effect, when a small number of initial founders establish a population which hence starts with a correspondingly small degree of genetic variation. Epigenetic inheritance involves heritable changes in phenotype (appearance) or gene expression caused by mechanisms other than changes in the DNA sequence.
Human phenotypes are highly polygenic (dependent on interaction by many genes) and are influenced by environment as well as by genetics.
Nucleotide diversity is based on single mutations, single nucleotide polymorphisms (SNPs). The nucleotide diversity between humans is about 0.1 percent (one difference per one thousand nucleotides between two humans chosen at random). This amounts to approximately three million SNPs (since the human genome has about three billion nucleotides). There are an estimated ten million SNPs in the human population.
Research has shown that non-SNP (structural) variation accounts for more human genetic variation than single nucleotide diversity. Structural variation includes copy-number variation and results from deletions, inversions, insertions and duplications. It is estimated that approximately 0.4 to 0.6 percent of the genomes of unrelated people differ.
Genetic basis for race Much scientific research has been organized around the question of whether or not there is genetic basis for race. In Luigi Luca Cavalli-Sforza's book (circa 1994) "The History and Geography of Human Genes" he writes, "From a scientific point of view, the concept of race has failed to obtain any consensus; none is likely, given the gradual variation in existence. It may be objected that the racial stereotypes have a consistency that allows even the layman to classify individuals. However, the major stereotypes, all based on skin color, hair color and form, and facial traits, reflect superficial differences that are not confirmed by deeper analysis with more reliable genetic traits and whose origin dates from recent evolution mostly under the effect of climate and perhaps sexual selection".
A 2015 review article concludes that with advances in detecting and dating admixture (mixing of groups), there is more evidence that admixture between populations has occurred throughout human history. Genetic differences between races are generally correlated to geographic distance.
In 2018 geneticist David Reich reaffirmed the conclusion that the traditional views which assert a biological basis for race are wrong:
In 1956, some scientists proposed that race may be similar to dog breeds within dogs. However, this theory has since been discarded, with one of the main reasons being that purebred dogs have been specifically bred artificially, whereas human races developed organically. Furthermore, the genetic variation between purebred dog breeds is far greater than that of human populations. Dog-breed intervariation is roughly 27.5%, whereas human population intervariation is only estimated to be between 5.4% and 15.6%.
Research methods Scientists investigating human variation have used a series of methods to characterize how different populations vary.
Early studies of traits, proteins, and genes
Early racial classification attempts measured surface traits, particularly skin color, hair color and texture, eye color, and head size and shape. (Measurements of the latter through craniometry were repeatedly discredited in the late 19th and mid-20th centuries due to a lack of correlation of phenotypic traits with racial categorization.) In actuality, biological adaptation plays the biggest role in these bodily features and skin type. A relative handful of genes accounts for the inherited factors shaping a person's appearance. Humans have an estimated 19,000–20,000 human protein-coding genes. Richard Sturm and David Duffy describe 11 genes that affect skin pigmentation and explain most variations in human skin color, the most significant of which are MC1R, ASIP, OCA2, and TYR. There is evidence that as many as 16 different genes could be responsible for eye color in humans; however, the main two genes associated with eye color variation are OCA2 and HERC2, and both are localized in chromosome 15.
Analysis of blood proteins and between-group genetics
Before the discovery of DNA, scientists used blood proteins (the human blood group systems) to study human genetic variation. Research by Ludwik and Hanka Herschfeld during World War I found that the incidence of blood groups A and B differed by region; for example, among Europeans 15 percent were group B and 40 percent group A. Eastern Europeans and Russians had a higher incidence of group B; people from India had the greatest incidence. The Herschfelds concluded that humans comprised two "biochemical races", originating separately. It was hypothesized that these two races later mixed, resulting in the patterns of groups A and B. This was one of the first theories of racial differences to include the idea that human variation did not correlate with genetic variation. It was expected that groups with similar proportions of blood groups would be more closely related, but instead it was often found that groups separated by great distances (such as those from Madagascar and Russia), had similar incidences. It was later discovered that the ABO blood group system is not just common to humans, but shared with other primates, and likely predates all human groups.