Tuesday, December 26, 2017

Eurasians did not introduce SLC24A5 into Sub-Saharan Africa

There is a new paper on African skin pigmentation. This paper was published in Science. Below is the abstract.
Nicholas G. Crawford  et al .( 2017). Loci associated with skin pigmentation identified in African populations. http://science.sciencemag.org/content/358/6365/eaan8433.long


Despite the wide range of skin pigmentation in humans, little is known about its genetic basis in global populations. Examining ethnically diverse African genomes, we identify variants in or near SLC24A5, MFSD12, DDB1, TMEM138, OCA2 and HERC2 that are significantly associated with skin pigmentation. Genetic evidence indicates that the light pigmentation variant at SLC24A5 was introduced into East Africa by gene flow from non-Africans. At all other loci, variants associated with dark pigmentation in Africans are identical by descent in southern Asian and Australo-Melanesian populations. Functional analyses indicate that MFSD12 encodes a lysosomal protein that affects melanogenesis in zebrafish and mice, and that mutations in melanocyte-specific regulatory regions near DDB1/TMEM138 correlate with expression of UV response genes under selection in Eurasians.
Crawford  et al, 2017, claimed the research yielded the following results: 1) “The alleles associated with light pigmentation swept to near fixation outside of Africa due to positive selection, and we show that these lineages coalesce ~60 ka, corresponding with the time of migration of modern humans out of Africa”; and 2) “The most significantly associated single-nucleotide polymorphisms were at SLC24A5, a gene associated with pigmentation in Europeans. We show that SLC24A5 was introduced into East Africa >5 thousand years ago (ka) and has risen to high frequency.”
The results of this research are invalid. First of all, we know that Neanderthal and the first Europeans such as Bana man were dark skinned (Winters,2014).
The archaeological and craniometric evidence indicates that the pre-Indo-European people were probably highly pigmented (Winters,2014). There have been numerous “Negroid skeletons” found in Europe according to Boule and Vallois (1957). Diop (1991) discussed the Negroes of Europe in Civilization or Barbarism (pp. 25-68). Also W.E. B. DuBois, The World and Africa noted that “There was once a an “uninterrupted belt’ of Negro culture from Central Europe to South Africa” (p. 88).
Boule and Vallois (1957) reported the find of SSA skeletons at, Grotte des Enfants, Chamblandes in Switzerland, several Ligurian and Lombard tombs of the Metal Ages have also yielded evidences of a Negroid element.
Since the publication of Verneau’s memoir, discoveries of other Negroid skeletons in Neolithic levels in Illyria and the Balkans have been announced. The prehistoric statues, dating from the Copper Age, from Sultan Selo in Bulgaria are also thought to protray Negroids (Boule & Vallois, 1957).
In 1928 Rene Bailly found in one of the caverns of Moniat, near Dinant in Belgium, a human skeleton of whose age it is difficult to be certain, but seems definitely prehistoric. It is remarkable for its Negroid characters, which give it a resemblance to the skeletons from both Grimaldi and Asselar (Diop, 1991).
The ancestral alleles from La Bana and Luxemburg indicated that they were  dark skinned Europeans (Olalde et al., 2014). This make it clear early Europeans were not pale skinned as Tishkoff et al (2017) alleges. In Addition, Skoglund et al. (2014) investigated the pigmentation of ancient Europeans including skeletal remains from Ajvide 5, La Brana 1, and the Iceman. The analysis by Skoglund et al. (2014)determined that the pigmentation phenotype for these Europeans was dark skin.
The findings of Olalde et al, 2014 and Skoglund et al 2014 that the earliest Europeans were dark skin,  disputes Crawford   et al (2017), suggestion that as early as 60ka , “The alleles associated with light pigmentation swept to near fixation outside of Africa due to positive selection”. This genetic evidence for dark pigmented ancient Europeans was supported by the negro skeletons associated with ancient European sites (Boule & Vallois, 1957).
Crawford    et al (2017) maintains that the SLC24A5 alleles was introduced into East Africa from Europe 5kya. This probably did not happen because there is no archaeological evidence of a back migration of Eurasians in Africa.
Secondly, Crawford   et al (2017) argues that SLC24A5 alleles were deposited in East Africa by Eurasians, but this allele is found among African populations throughout Africa. The pigmentation center is SLC24A5. The ancestral gene for light skin rs1426L54 is “predominante” among sub-Saharan African (SSA) populations (Canfield et al., 2014). The derived allele from this coding polymerphism for light skin is A111T alleles (Canfield et al., 2014). The A111T pigmentation haplotype indicate high frequencies among “light skinned” populations in Europe and East Asia. The existence of the ancestral gene for light skin rs1426L54 , makes it clear Eurasians did not have to introduce  SLC24A5 because Sub-saharan Africans were already carrying the gene.
In conclusion, the findings of Crawford   et al (2017) are not supported either by archaeological or genetic evidence. As a result, this paper is unreliable and invalid..

Boule, M., & Vallois, H. V. (1957). Fossil Man. New York: Dryden Press.
Canfield, V. A., Berg, A., Peckins, S. et al. (2014). Molecular Phylogeography of a Human Autosomal Skin Color Locus under Natural Selection. G3, 3, 2059-2067.
Diop, A. (1991). Civilization or Barbarism. Brooklyn, NY: Lawrence Hill Books.
Olalde, I., Allentoft, M. E., Sanchez-Quinto, F., Santpere, G., Chiang, C. W. K., DeGiorgio, M. et al. (2014). Derived Immune and Ancestral Pigmentation Alleles in a 7,000-Year-Old Mesolithic European. Nature, 507, 225-228.

Winters, C. (2014). Were the First Europeans Pale or Dark Skinned?. Advances in Anthropology, 4, 124-132. doi: 10.4236/aa.2014.43016.

No comments: