November 02, 2010

African Pygmy news

Two new papers, one using mtDNA, one using skulls.

From the paper:
Shape variation indicates that western groups present longer vaults and shorter faces than eastern groups (Fig. 1B). Variation on PC2 involves differentiation in the shape produced mainly by the short distance between bregma and vertex (Fig. 2) being the vertex more anteriorly located in pygmies than in non-pygmies.

...

Differences in CS were significant (p less than0.05) and they concerns Western pygmies which show a smaller cranial size than both Eastern and Western non-pygmies; it is worth to note that Eastern pygmies do not show significant difference in size with any group


Also:
Results of the PCA indicate that the main cranial shape differentiation does not occur between pygmies and non-pygmies but between Eastern and Western populations (pygmies and non-pygmies) (Table 1; Fig. 1A); all comparison between East and West groups reach a high level of significance (p less than 0.01). Eastern non-pygmies appear as the most distinctive group and differentiate from pygmies and Western non-pygmies in relative and absolute values. Since western pygmies show a higher level of admixture than eastern pygmies, it can be expected that the former differentiate less than the latter from non-pygmies.

PLoS ONE 5(10): e13620. doi:10.1371/journal.pone.0013620

Diversity among African Pygmies

Fernando V. RamĂ­rez Rozzi, Marina L. Sardi

Although dissimilarities in cranial and post-cranial morphology among African pygmies groups have been recognized, comparative studies on skull morphology usually pull all pygmies together assuming that morphological characters are similar among them and different with respect to other populations. The main aim of this study is to compare cranial morphology between African pygmies and non-pygmies populations from Equatorial Africa derived from both the Eastern and the Western regions in order to test if the greatest morphological difference is obtained in the comparison between pygmies and non-pygmies. Thirty three-dimensional (3D) landmarks registered with Microscribe in four cranial samples (Western and Eastern pygmies and non-pygmies) were obtained. Multivariate analysis (generalized Procrustes analysis, Mahalanobis distances, multivariate regression) and complementary dimensions of size were evaluated with ANOVA and post hoc LSD. Results suggest that important cranial shape differentiation does occur between pygmies and non-pygmies but also between Eastern and Western populations and that size changes and allometries do not affect similarly Eastern and Western pygmies. Therefore, our findings raise serious doubt about the fact to consider African pygmies as a homogenous group in studies on skull morphology. Differences in cranial morphology among pygmies would suggest differentiation after divergence. Although not directly related to skull differentiation, the diversity among pygmies would probably suggest that the process responsible for reduced stature occurred after the split of the ancestors of modern Eastern and Western pygmies.

Link

Next paper:

Mol Biol Evol (2010) doi: 10.1093/molbev/msq294

Insights into the demographic history of African Pygmies from complete mitochondrial genomes

Chiara Batini et al.

Pygmy populations are among the few hunter-gatherers currently living in sub-Saharan Africa and are mainly represented by two groups, Eastern and Western, according to their current geographical distribution. They are scattered across the Central African belt and surrounded by Bantu-speaking farmers, with whom they have complex social and economic interactions. To investigate the demographic history of Pygmy groups, a population approach was applied to the analysis of 205 complete mitochondrial DNA (mtDNA) sequences from ten central African populations. No sharing of maternal lineages was observed between the two Pygmy groups, with haplogroup L1c being characteristic of the Western group, but most of Eastern Pygmy lineages falling into sub-clades of L0a, L2a and L5. Demographic inferences based on Bayesian coalescent simulations point to an early split among the maternal ancestors of Pygmies and those of Bantu-speaking farmers (∼70,000 ya, years ago). Evidence for population growth in the ancestors of Bantu-speaking farmers has been observed, starting ∼65,000 ya, well before the diffusion of Bantu languages. Subsequently, the effective population size of the ancestors of Pygmies remained constant over time and ∼27,000 ya, coincident with the Last Glacial Maximum, Eastern and Western Pygmies diverged, with evidence of subsequent migration only among the Western group and the Bantu-speaking farmers. Western Pygmies show signs of a recent bottleneck 4,000 – 650 ya, coincident with the diffusion of Bantu languages, while Eastern Pygmies seem to have experienced a more ancient decrease in population size (20,000 - 4,000 ya). In conclusion, the results of this first attempt at analysing complete mtDNA sequences at the population level in sub-Saharan Africa not only support previous findings but also offer new insights into the demographic history of Pygmy populations, shedding new light on the ancient peopling of the African continent.

Link

4 comments:

Andrew Oh-Willeke said...

L0a, L1c, and L5 are generally associated with Khoisan/Pygmy populations. Would L2a presumably represent a Bantu farmer contribution?

German Dziebel said...

"No sharing of maternal lineages was observed between the two Pygmy groups, with haplogroup L1c being characteristic of the Western group.."

In the very least, this study shows that Western Pygmies are really Bantu and Ubangian populations who entered the rain forest either before the advent of agriculture or shortly after. They are not an "ancient" population that adopted Niger-Congo languages. They ARE Niger-Congo populations. L1c is the lineage they uniquely share with Bantu and Ubangian speakers but not with Eastern Pygmies. A perfect correspondence between genetics and linguistics here.

"Demographic inferences based on Bayesian coalescent simulations point to an early split among the maternal ancestors of Pygmies and those of Bantu-speaking farmers (∼70,000 ya, years ago). Evidence for population growth in the ancestors of Bantu-speaking farmers has been observed, starting ∼65,000 ya, well before the diffusion of Bantu languages."

This is a testament to how hopelessly wrong geneticists' dates are (especially in Africa). How could Bantu-speaking farmers have expanded 65,000 YA? If these dates are about the expansion of the maternal ancestors of Bantu farmers, then we really shouldn't be talking about Bantu. All these presumably ancient African lineages are likely of Holocene age.

eurologist said...

Or, alternatively, the most remote lineages are 500,000 to 200,000 years old. Which I find better established overall and more believable.

German Dziebel said...

This will place the expansion of Bantu speakers at some 100,000 YBP, right? I'm afraid you'll have to dig up some evidence for agriculture in Blombos Cave. Just because African lineages show homoplasies with chimps doesn't make them old.