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Ancient west Eurasian ancestry in southern and eastern Africa 2013
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[QUOTE]Originally posted by The Explorer: [QB] From blog entry, "[i]Haplogroup Assignment; Old Habits that Die Hard"[/i], June 30, 2013: Pagani et al.'s practice steers clear away from the real complexities of human phylogeny, by hinging their assignment effortlessly on what is considered an "L" clade and what is not, and thereof, facilitating assignment into two neat, seemingly non-overlapping, ancestral lines. The basis for the assignment of remaining segments of the genome, which were not mitochondrial, into an identical two-party grouping of ancestral lines (African and non-African respectively), was mostly left to the imagination of the reader. The few exceptions therein, where the DNA locus was implicated by the name of a gene, as was the case of the SLC24A5 gene, "frequency" was alluded to as the reasoning behind the assignment into one of the two camps of ancestry. The "derived" variant of the SLC24A5 gene was taken for granted as "non-African" on the mere account of its high "frequencies" in European samples, but it was demonstrated [2] that the distribution pattern of the variant, along with the relevant attributes of other pigmentation genes, elicited caution against that assumption. Among other sub-Saharan groups, the "derived" variant of the SLC24A5 appears in the gene pool of the San, as have "derived" variants of other known "skin pigmentation" genes. [b]The easing up of skin eumelanin in San hunter-gatherers has generally been attributed to local evolution in lower UV radiation environments they frequent, as opposed to the result of gene flow[/b]. In the Ethiopian samples, on the other hand, the presence of the "derived" variant of the SLC24A5 gene was peculiar in that it was not found in tandem with other "skin-pigmentation" affiliated genes whose distribution generally paralleled that of the "derived" SLC24A5 variant, particularly in Europeans. Hence, "frequency" in itself is not a sufficient enough indicator for ascribing a single-source origin in the form of a "non-African" origin. - Extract ends From blog entry, "[i]What Ethiopian Genetic Diversity—Really—Reveals![/i]", May 15, 2013: This [SLC24A5] gene, in its derived form, which is said to be under positive selection in "lightly" pigmented populations, was [b]implicated in the San[/b], who as noted above, [b]tend to generally be isolated[/b], and [b]culturally-conservative hunter-gatherers[/b]. [b]"Derived" variants[/b] of [b]other[/b] pigmentation-associated genes were also cited, [b]with respect to the San[/b]([5]). It is [b]questionable that this gene is serving as a "non-African" marker in the San[/b]. The [b]same issue actually surfaces with regards to its presence in Ethiopian[/b] groups: Secondly: [i][b]Given that SLC24A5 is one of the most highly differentiated genes between African and European[/b] populations, we then [b]looked for other highly differentiated genes[/b] among the outlier windows, [b]but found none[/b]... To [b]further investigate the effect of admixture on the genetic landscape of skin pigmentation in Ethiopia[/b], we also [b]looked at other genes associated with pigmentation in Europe[/b]; however, [b]none were found in our outlier regions[/b].[/i] If this gene, in its "derived" form, was essentially serving as a "non-African" marker in the Ethiopians, then [b]one would expect that other "derived" skin-pigmentation markers would have been introduced along with the SLC24A5 allele[/b], by the foreign "non-African" group(s) that is supposed to have been the source. [b]Skin pigmentation is the byproduct of the consortial work of a number of distinct genes[/b], and [b]so, it's highly unlikely that a "derived" SLC24A5 allele would be introduced without other accompanying skin-pigmentation genes[/b]. No less, it's [b]highly unlikely that only the derived "SLC24A5" allele would survive[/b] from a foreign "non-African" source, [b]in a population for which the allele's presence is "potentially disadvantageous"[/b], as the authors note, on grounds of the kind of UV-radiation intensive environment they generally reside. Likewise, [b]if as the authors note[/b], the [b]presence of the derived SLC24A5 allele in Ethiopians may be attributable to "socially"-promoted selection[/b], then one would think that [b]other skin-pigmentation genes, which would have accompanied the SLC24A5 allele[/b] in an introduction by a foreign "non-African" source, [b]would have likely also survived in some capacity or another[/b], so as [b]to serve the same role that the SLC24A5 may be serving[/b]. --Extract ends As any rational person will glean from these notes, the issues raised undoubtedly emerge from a scientific and objective groundwork. Kwadi is essentially an extinct KhoiSan language group, and it is fairly known that speakers of said language had largely integrated into surrounding non-KhoiSan speakers. Hence, it is not surprising to find considerable non-KhoiSan ancestry in elements of Kwadi groups. The San hunter-gatherers on the other hand, as noted above, still maintain their traditional lifestyles and have remained largely isolated from non-KhoiSan groups. This means that they retain mainly their ancestry from before other groups intruded on traditional KhoiSan territory. KhoiSan territory spans southern Africa, and as mentioned, these groups have naturally adapted to the sub-tropical environments of southern Africa. Bottom line is, there is no evidence whatsoever that the San hunter-gatherers have earned their relaxed skin-pigmentation from "Eurasians", and thus would not have been "light" without such foreign input, as opposed to a natural adaptation to their environment. [/QB][/QUOTE]
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