Population substructure in Europe – Northwest to Southeast cline?

Share on FacebookShare on Google+Email this to someoneTweet about this on Twitter

The American Journal of Human Genetics has an article up examining population substructure within Europe (or, more precisely, the varation of genes), Measuring European Population Stratification with Microarray Genotype Data. From the discussion:

PC1 [the largest principle component of variance] largely separates northern from southeastern individuals…and is consistent with the clines observed in classic gene-frequency…Y-chromosome…mtDNA…and whole-genome…studies of European diversity. PC2 [the second largest principle component of variance] reflects mainly east-west geographic separation and, particularly, identifies the two Iberian populations (Spanish and Basques) in our analysis as distinct…Furthermore, PC3 and PC4 emphasize the separation of the Basques and Finns, respectively, from other Europeans…The Basques are known to have unusual allele frequencies for several marker systems…and speak a unique non-Indo-European language. In line with their non–Indo-European Uralic language and previous study of their Y-chromosomesthe Finns show evidence of an increased affinity to the Central Asian populations when placed in an intercontinental context…STRUCTURE analysis of the European populations is highly consistent with PCoA; for example, when the number of populations (K) is 3, the major divisions correspond to the northern, southeastern, and Iberian populations…In cases of higher K values, first the Finns (K = 4) and then the Basques (K = 5) emerge as distinctive….

The southeast-north cline that they speak of is straight out of L.L.Cavalli-Sforza’s History and Geography of Human Genes. Cavalli-Sforza argued in that book that this reflected the “demic diffusion” of agriculture and was a residue from a genetic wave of advance generated by population expansion initiated in the region of the Levant-Anatolia. By its nature a wave of advance is exhibits a weaker genetic signal in relation to the source because of dilution via intermarriage, so it is no surprise that the British, for example, are predominantly descended from the Paleolithic hunter-gatherers of northern Europe. The detection of east-west gradients, as well as the diversity of the Iberian sample, also points to the demographic expansions out of the Ice Age refugia when the glaciers retreated and northern Europe was repopulated. Note that the sample sizes for some of the local populations were very small. From the paper, “western Irish (n = 6), eastern English (n = 8), French (n = 1), German (n = 8), Valencian Spanish (n = 20), Basque Spanish (n = 8), Italian (n = 9), Polish (n = 8), Greek (n = 8), Finnish (n = 7), Armenian (n = 8), and Ashkenazi Jewish (n = 5)….” I’ve placed the most informative figure below the fold as a high res image.

Related: Jaakkeli says….

Labels:

17 Comments

  1. The wide range of the Italian datapoints is interesting. It’s tempting to say that this corresponds to the well-known north/south cultural cline within Italy, but with so few datapoints that might be premature.  
    I’m also not surprised that Polish/German/East English/West Irish are more or less overlapping. A keen student of human morphology might be able to sort members of those groups with better than random accuracy, but it wouldn’t be easy.

  2. And their food is indistinguishably disgusting. 
     
    As opposed to Italian.

  3. At this point I really believe that the various pagan, preliterate Northern European cultures (Germanic, Celtic, Baltic, Slavic) are not sharply distinguished the way their languages are. If you abstract out culture-independent features such as geographical features impacting way of life, relationships with the civilizations of the Mediterranean and the Middle East, agricultural environments, military situations, etc., Slavicness, Balticness, Germanness, and Celticness diminish enormously.  
     
    For example, the different ways of handling the dead were used for a long time to distinguish culture, but the more information we get the less helpful this marker becomes.

  4. The wide range of the Italian datapoints is interesting. It’s tempting to say that this corresponds to the well-known north/south cultural cline within Italy, but with so few datapoints that might be premature. 
    I’m also not surprised that Polish/German/East English/West Irish are more or less overlapping. A keen student of human morphology might be able to sort members of those groups with better than random accuracy, but it wouldn’t be easy.
     
     
    there are data which would suggest that a lot of britons have more a greater affinity with iberians than they do with eastern europeans. the romans in fact thought the welsh were related to the iberians because of their physique. in any case, i think this is a very rough model of what might be going on with europe’s gene frequencies: 
     
    1) 30-25 years ago europe was populated by a amorphous population of moderns whose ancestors came from the middle east 
     
    2) during the last glacial maximum 20 years ago this population retreated to two pools, in iberia and along the southeast fringe in ukraine. there might have been smaller pockets along the southern european littoral, but these were a minority 
     
    3) after the ice retreated there were two demographic waves which immediately swept northeast and west respectively from the two refugia. both of these populations had their origins in the early settlement of europe, but they had diverged during the glacial maximum. 
     
    4) with the rise of agriculture another demographic swept out of southeast european-anatolia. this is a more genetically different pulse (that is, the common ancestors are further back) 
     
    this is explains why the south/southeast to north/northwest gradient seems somewhat stronger than the east to west gradient. the east to west gradient is the overlap of two groups of core ice age european populations, while the southeast to northwest is a signal with at least some middle eastern antecedents. 
     
    don’t know if i buy the story, but that’s what i’ll offer for now.

  5. At k=6, what do you suppose the Pink color represents? 
     
    Could this be just background noise, or something more exotic, like Neanderthal??

  6. a lot of britons have more a greater affinity with iberians than they do with eastern europeans. the romans in fact thought the welsh were related to the iberians because of their physique 
     
    The British are probably more closely related to northern Iberians than they are to southern ones. Also the Moors may have affected the gene pool of modern Iberia.

  7. The British are probably more closely related to northern Iberians than they are to southern ones. Also the Moors may have affected the gene pool of modern Iberia. 
     
    yes, your supposition is correct insofar as basques are used as the iberian ‘control’ in most of these studies. the moors didn’t have much of an impact btw (pehaps some, but not much) genetically if you mean north african ancestry. the moors by the 16th century were probably mostly the descendents of converts (even if they could trace patrilineages, these would be diluted). also, if you look at the figure you can see that basques (northern iberians) are displayed separately from spanish speakers. though i would be cautious about looking too closely at the fine grained clusters when considering the n’s i note above.

  8. As for the results in Italy, it would be interesting to look at the regional origins of the sample in light of the north-south genetic gradient that most of the Y-chromosome studies have found.  
    Italy is a difficult country to discuss in terms of genetic history because it seems to be among the most genetically stratified by region (at least based on Cavalli-Sforza’s work and more recent Y-chromosome studies). 
    A bigger sample size would be much better; my assumption is that those who ended up in the southeastern cluster were of southern/central Italian origin (regions settled by Greek and Anatolian migrants in protohistoric times) and those in the northern/western cluster were of northern Italian origin.

  9. there have been previous studies on italians. e.g., 
     
    Trends in both the Italian and Spanish participants were also consistent with this north?south pattern: ten of 32 participants from northern Italy had greater than a 10% ?northern? component compared with two of 28 from southern Italy; and 23 of 43 from northern Spain had greater than a 10% ?northern? contribution compared to five of 19 from southern Spain. 
     
    cite. the n here is way bigger (i think 92 italians total).

  10. The British are probably more closely related to northern Iberians than they are to southern ones. Also the Moors may have affected the gene pool of modern Iberia. 
     
    As someone mentioned the Moors seem to have had little impact in Spain, just as the Turks seem to have little impact in Greece. Most of the population that was Moslem were in fact converts. 
     
    As for as reasons for diversity in Iberia from Britain, the likely explanation would be the western Goths who were not a raiding group or small elite but a mass population in search of land.

  11. As for as reasons for diversity in Iberia from Britain, the likely explanation would be the western Goths who were not a raiding group or small elite but a mass population in search of land. 
     
    they were a mass population (i mean, we can project based on the size of their warbands), but they still didn’t have a large impact from what i can see genetically. otherwise, you’d see a lot more r1a haplotype in spain (like you do in east anglia in england).

  12. From reading Heather, while the Goths who came from the Baltic to the borders of Rome traveled en masse (over a considerable period of time), I believe that as they went from the Danube to Italy to Southern France to Spain their numbers decreased at each step.  
     
    When the Goths filled the vacuum left by the passing of the Roman Empire, they didn’t really need large numbers, since Roman citizens were civilianized and the Roman military was gone. 
     
    The Goths were also not genetically uniform — they were a Goth-led military force made up of whichever soldiers were evailable, including Huns, Alans, and so one.

  13. john e., yeah, what you are describing is a fisherian ‘wave of advance.’

  14. Well, as I am their descendant, I thought that it might be interesting to see what tribes also invaded Europe :) 
    “Asparuh, the successor to Kubrat, subsequently conquered Moesia and Dobrudja from the Byzantine Empire in 680 and formed the First Bulgarian Empire.” This part is my favourite as I was born in Dobrudja only the year must be 681 :))

  15. Does anyone here give any credence to the Gutians = Jats = Goths theory??

  16. Gutians = Jats = Goths  
     
    no.

  17. britons have more a greater affinity with iberians than they do with eastern europeans 
     
    That’s just on the Y-chromosome.

a