This guest post on race is by Jared of the ever excellent LDS Science Review.
When I was an undergraduate at BYU one of my professors told our class the story of an experience he had while conducting a genetic study that included residents of Utah. In the course of the study he determined that in a certain family, a daughter was not the biological offspring of the father. He met with the family to explain the findings relevant to the study and was asked by the father about the daughter. After an awkward moment my professor told the father that the daughter was not his genetic offspring. To my professor’s relief this was not a surprise to the father–but the father had a different problem. The family was LDS and the daughter had been sealed to him. At the sealing the officiator told the family something to the effect that the daughter’s blood had been changed. This father expected his daughter’s genetic identity to reflect this change. My professor managed the best answer he could–that whatever the changing of blood meant, it didn’t mean a change in genetic identity.
This story (told to the best of my memory) is one example of the difficulties we sometimes have overlaying our theological and scriptural concepts of lineage and race onto our growing scientific understanding. In the wake of a recent post, Ronan invited me to provide some scientific perspective on race. I should state that I don’t have any special training in anthropology or population genetics. What I present here is my understanding based on some limited reading in the scientific literature.
Perhaps the best way to put race into perspective is to begin with the emergence of humans. Archaic humans developed in Africa and began to spread out into Europe and Asia around 2 million years ago. Anatomically modern humans emerged around 200,000 years ago in Africa and a subset of that population began expanding out of Africa and into Europe, Asia, and Australia around 50,000 years ago. Although there is still some debate, the emerging picture indicates that there was some interbreeding between the modern and archaic humans with archaic humans ultimately going extinct. Modern humans then spread from Asia into North America around 15-20,000 years ago. This general scheme is supported by both fossil and genetic evidence.
As humans expanded into new territories and became isolated from one another for both geographical and cultural reasons, it makes sense that populations would begin to diverge from one another genetically and develop adaptations to their environment, thus giving rise to populations differing in morphology and in genetic make-up. However the degree of divergence should not be overstated. Humans are more homogeneous than many other species, including chimpanzees. The variation between human groups accounts for only 10-15% of total human genetic variation–the remaining 85-90% is shared.
The term ‘race’ has a number of imprecise meanings and is used in ways that encompass culture, religion, demographics, and visible morphology. In terms of zoological classification and systematics, humans do not meet the criteria for subspecies. So usage of the term ‘race’ as a synonym of ‘subspecies’ is not supported for humans. Nevertheless genetically similar people do tend to cluster geographically and a person’s genotype can be used to infer their geographic area of ancestry, although there are rarely any sharp lines of demarcation. (For efforts to correlate genetics with geography and ancestry, see here.) There is no such thing as a genetically ‘pure’ population.
It is intuitive that people from different regions look different from one another. Africans look different than Scandinavians–there must be some genetic basis for this difference. My impression is that the genetic basis for many ‘racial’ traits is poorly understood. There is not a simple one-to-one relationship between a particular gene and skin color, for example. Rather, a number of genes appear to play a role, which makes the connection between genotype and phenotype difficult. The darkness of skin color does generally correlate with UV exposure and inversely correlate with latitude, and is thought to represent an adaptation generated by natural selection. However as far as I am aware, the timing of the development of outward racial features in human history is largely unknown.
Recently Lamason et al. identified a gene that affected pigmentation in zebrafish. Extending their work to humans, they found two variants of the gene that correlate strongly with either African or East Asian populations versus European populations. The African form of the gene can be inferred to be the ancestral form and appears to account for about 30% of the difference in skin pigmentation between Africans and Europeans. That the ancestral form is also present in East Asians indicates that other genes play a role in their lighter skin color.
Prominent racial physical features can seduce us in to forgetting the much more complicated genetics that can exist in a person of a given race. What we see in the outward appearance represents only a small part of the genome. This is illustrated in a study by Parra et al. where Brazilians were tested for alleles indicative of European or African ancestry. They found that on an individual level, color was a poorly predictive of genomic African ancestry, based on molecular markers.
In spite of the problems of racial designations, they do serve some practical value in a scientific setting. For example, certain racial groups are known to be at higher risk for the development of various medical problems. In the absence of genetic analysis, race can serve as a useful (though imprecise) proxy and aid in the diagnosis and treatment of disease.
Overlaying a traditional LDS understanding of race and lineage onto the above information leads to a number of difficulties. Fortunately one of the greatest difficulties, the denial of priesthood to blacks and the attendant theological justifications, is now behind us. I look forward to the resolution of remaining ones.
References and Further Reading:
(Note: Most of the references I provide here are freely available online.) Nature Genetics 36, (01 Nov 2004) has several articles on race. See particularly Jorde and Wooding, “Genetic variation, classification and ‘race,’ and Keita, et al., “Conceptualizing human variation.” Barsh, What Controls Variation in Human Skin Color?, PLOS Biology Vol. 1 (1) 2003. Lamason et al., SLC24A5, a Putative Cation Exchanger, Affects Pigmentation in Zebrafish and Humans, Science, Vol. 310 No. 5755. (Abstract only–subscription required.) Parra et al., Color and genomic ancestry in Brazilians, Proceedings of the National Academy of Sciences, 100 (1): 177. Also see the Wikipedia entry for race.