March 26, 2011

Pastoral and farmer populations from the Sahel

In Central Asia, the expansion of the Mongol nomads led to the predominance of a few Y-chromosome lineages of relatively recent vintage. The opposite seems to be true for the African pastoralists examined here: they see to be more diverse in their Y-chromosomes than farmers are, and less so in their mtDNA. This suggests that they were a fairly old group who did not particularly marry farmers' daughters.

Mol Biol Evol (2011) doi: 10.1093/molbev/msr067

Genetic structure of pastoral and farmer populations in the African Sahel

Viktor Černý et al.

Traditional pastoralists survive in but few places in the world. They can still be encountered in the African Sahel, where annual alternations of dry and wet seasons force them to continual mobility. Little is known about the genetic structure of these populations. We present here the population distribution of 312 HVS-I mtDNA and 364 Y-STR haplotypes in both farmer and pastoralist groups from the Lake Chad Basin and the West African Sahel. We show that the majority of pastoral populations (represented in the African Sahel by the Fulani nomads) fail to show significant departure from neutrality for mtDNA as evidenced by Fu's Fs statistics, and exhibit lower levels of intra-population diversity measures for mtDNA when contrasted with farmers. These differences were not observed for the Y chromosome. Furthermore, AMOVA analyses and population distributions of the mtDNA haplotypes show more heterogeneity in the sedentary groups than in the pastoralists. On the other hand, pastoralists retain a signature of a wide phylogenetic distance contributing to their male gene pool, whereas in at least some of the farmer populations a founder effect and/or drift might have led to the presence of a single major lineage. Interestingly, these observations are in contrast with those recorded in Central Asia, where similar comparisons of farmer and pastoral groups have recently been carried out. We can conclude that in Africa there have been no substantial mating exchanges between the Fulani pastoralists coming to the Lake Chad Basin from the West African Sahel and their farmer neighbors. At the same time we suggest that the emergence of pastoralism might be an earlier and/or a demographically more important event than the introduction of sedentary agriculture, at least in this part of Africa.

Link

14 comments:

AdygheChabadi said...

Unfortunately, this paper does not include any high-resolution phylogenetic analysis of the mtDNA or the Y-SNP's.

argiedude said...

Did you look at the study, Adyghe? What does it show? Haplotypes, SNP tables?

Eze said...

These findings are in agreement with the autosomal data on Fulanis in Bryc & Henn et al. They are notably divergent from neighboring sedentary groups, which couldn't be explained by a function of geography.

Annie Mouse said...

This should be viewed in conjunction with:

http://dienekes.blogspot.com/2011/03/clusters-galore-analysis-of-henn-et-al.html

Which showed low level European admixture in the Fulani (IMO); and relationships with other pastorialists and hunter gatherers (Maasai, Sandawe, San).

AdygheChabadi said...

Hi, and, yes, Argiedude, I have the paper...I saw no high-resolution data at all. It makes references to R1b-V88, "E3b-M35", and "E3a-M2"...but no SNP data of any interest.

Seems like this paper was started years ago and just now got published.I say that because of the old Y-SNP nomenclature used in those references.

Even the haplotypes are basic...just 8 markers...They did include the often left out DYS388 marker. It does not make the haplotype tables available.

I have seen no supplements to this paper...

Countries like Chad and Niger are so genetically understudied...The authors missed a very rare opportunity to shed some light here...thankful for what they did shed light on though.

Strat said...

"This should be viewed in conjunction with:

http://dienekes.blogspot.com/2011/03/clusters-galore-analysis-of-henn-et-al.html

Which showed low level European admixture in the Fulani (IMO); and relationships with other pastorialists and hunter gatherers (Maasai, Sandawe, San)."

Annie Mouse, what relationship of the Fulani with the San does it show? According to that MDS plot, the unadmixed San are genetically the most distant Sub-Saharan population to the Fulani.

andrew said...

"We can conclude that in Africa there have been no substantial mating exchanges between the Fulani pastoralists coming to the Lake Chad Basin from the West African Sahel and their farmer neighbors."

Query if they find any exchanges between Fulani pastoralists and pastoralistics that speak Chadic languages (e.g. Hasua), Nilo-Saharan languages (e.g. Maasai), or Berber languages?

Also of interest are how complete the Fulani sample is geographically, and whether Fulani are closer genetically to other Niger-Congo language speaking farmer populations than non-Niger-Congo langauge speaking pastoralist populations are to Niger-Congo language speaking farmer populations.

It would also be interesting to see how closely the genetic evidence corresponds to the historical and legendary accounts of Fulani origins. For example, my understanding is that the Fulani are relative latecomers to the Lake Chad basin, yet the study seems to indicate that their existence of a coherent cultural unit may predate the Niger-Congo language speaking farmers they are adjacent to in Africa.

Annie Mouse said...

@Strat

If you look at the first figure the 2 diminsional plot, you can see that several lines of relationship exist.

One line includes the San and the Fulani (at either end) indicating that these groups are part of a relationship group with positions on the line indicating relative admixture. A spectrum of relationship if you like.

Annie Mouse said...

OK perhaps it would be clearer to say that the San and the Fulani are not related, but they are both parts of a relationship group. They are the poles in the relationship group. With the other groups representing variable admixtures of Fulani and San (or something very like the San).

Strat said...

Mouse, according to that MDS plot there is no relationship between the Fulani and the unadmixed San that they don't share with all the other Sub-Saharan African populations (including the agriculturalists). Their genetic divergence is stark.

Annie Mouse said...

@Stat

If you read what I say, I say they are in a relationship group. They are part of a connected set of related populations. The relationship spans from San to Fulani. But does not include other groups like the Bantu for example. They do not have to genetically connected if they are at poles of the group.

IMO being part of a relationship group is more significant than absolute distance.

In admixtured populations distance is heavily influenced by the admixture composition. So two genetically similar populations that have not been in contact for millenia will appear closer than an admixtured population made up of diverse populations. Or put another way. Mom may be Japanese, Dad may be European. The child appears Uiger or Indian. But un fact the chid is more closely related to the Japanese and Europeans than first appears. And indeed clearly Japanese Mom met European Dad.

I am reading this as significant contact between hunter gathers (San-like) and pastorialists (Fulani).

Strat said...

"If you read what I say, I say they are in a relationship group. "They are part of a connected set of related populations. The relationship spans from San to Fulani. But does not include other groups like the Bantu for example."

"I am reading this as significant contact between hunter gathers (San-like) and pastorialists (Fulani)."

Where is the evidence for these?

Annie Mouse said...

"Where is the evidence for these?"

The plot is the evidence.

Strat said...

"The plot is the evidence."

I think what that plot shows at most is a relationship between the pre-Bantu East African populations (Hadza, Sandawe and Maasai). Fulani's position is probably due to their connections with both Western Africa and Northern Africa (not necessarily recent, but their heterogeneous position brings to mind at least some recent connections). The unadmixed San have no visible relationship with these populations according to the plot; on the other hand, they are on the same vertical axis with the unadmixed Pygmies, this may point to a relationship between the two.