October 23, 2004

Craniofacial variation of northeast Africans

A new article by S.O.Y. Keita examines craniofacial variation in northeast African populations. Two points need to be made: first, the greater degree of morphological variation in the several African populations is expected due to their wider geographical dispersion, compared e.g., to the three European populations from Austria, Hungary and Norway.

Second, Keita injects some commentary into this article regarding the wide variation of phenotypes associated with the YAP+ Y-chromosomal lineage:

All of the African populations represented in this study, or related peoples, are either in the PN2 or YAP+ ‘‘family’’ at some substantial level. From a general evolutionary perspective, the PN2 clade trenchantly demonstrates the point that individuals/populations having a tremendous range of physical traits, the focus of traditional approaches, can have fairly recent common ancestry in terms of lineage, i.e., can derive substantively from a common population, and therefore, in this sense, be more related than they are to others to whom they may be more phenetically similar in craniometric pattern (or classical polymorphisms).

Of course this argument for the alleged phenotypic plasticity of YAP+ Africans (almost all of which belong to haplogroup E) fails to account for the alternative explanation for their wide craniofacial variation, namely admixture. North Africans who belong to haplogroup E have very small occurrence of the archaic proto-human lineages A and B, and of matrilineages found in Sub-Saharan Africa. So, they are probably different from Negroids due to the fact that they're overall genetic makeup is different, even if they are linked by common ~30ky old Y-chromosomal lineage.

American Journal of Human Biology
Volume 16, Issue 6 , Pages 679 - 689

Exploring northeast African metric craniofacial variation at the individual level: A comparative study using principal components analysis

S.O.Y. Keita


A principal components analysis was carried out on male crania from the northeast quadrant of Africa and selected European and other African series. Individuals, not predefined groups, were the units of study, while nevertheless keeping group membership in evidence. The first principal component seems to largely capture size variation in crania from all of the regions. The same general morphometric trends were found to exist within the African and European crania, although there was some broad separation along a cline. Anatomically, the second principal component captures predominant trends denoting a broader to narrower nasal aperture combined with a similar shape change in the maxilla, an inverse relation between face-base lengths (projection) and base breadths, and a decrease in anterior base length relative to base breadth. The third principal component broadly describes trends within Africa and Europe: specifically, a change from a combination of a relatively narrower face and longer vault, to one of a wider face and shorter vault; it shows the northeast quadrant Africans along a cline with the other Africans. Stated in relative terms, the northeastern Africans tend to exhibit narrower bases in relationship to more projecting faces, and broader nasal areas than Europeans, although there is range of variation. Relative to the other African groups, they have narrower nasal areas and narrower faces in relationship to vault length. The crania from the northeast quadrant of Africa collectively demonstrate the greatest pattern of overlap with both Europeans and other Africans. Variation was found to be high in all series but greatest in the African material as a whole. Individuals from different geographical regions frequently plotted near each other, revealing aspects of variation at the level of individuals that is obscured by concentrating on the most distinctive facial traits once used to construct types. The high level of African interindividual variation in craniometric pattern is reminiscent of the great level of molecular diversity found in Africa. These results, coupled with those of Y chromosome studies, may help generate hypotheses concerning the length of time over which recent craniometric variation emerged in Africa.


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