My main observations after reading this study are:
- relative genetic homogeneity in Europe, with a fairly small percentage of variance explained by geographic differentiation
- clinal, rather than racial apportionment of European genetic variation, with no emerging separated clusters (except the Finns, who stand at some distance along the first eigenvector)
- south-north (but not east-west) decrease in genetic variation and heterozygosity indicating that Europe was populated on a south-north axis, rather than an east-west one.
- clear clustering of individuals from different ethnic groups within the European continuum, indicating that ethnic groups are not only cultural, but to some extent biological entities.
- Some ethnic groups are clearly distinguishable from each other (e.g. Swedes vs. Spaniards); some groups are partitioned into fairly disjoint sets (Spain I vs. Catalans in Spain II); others mutually overlap (e.g., British and Irish); while others overlap asymetrically (e.g., some former Yugoslavs in the Greek cluster, but not vice versa).
Interestingly Italians neighbor Spaniards on the other side; whereas former Yugoslavs neighbor Czechs.
A straightforward explanation for this pattern is that the Italian groups has mixed Western and Eastern Mediterranean affiliations; the latter stemming from either Neolithic farmers or Greek (or Etruscan, etc.) colonists.
Former Yugoslavs are mostly disjoint from Greeks, except some who seem to be Slavicized Greeks, consistent with their descent from indigenous Balkan populations on one hand and Slavic immigrants more akin to Czechs and Poles on the other. Thus, they occupy an intermediate position between Greeks and Czechs.
From the paper:
Hierarchical analysis of molecular variance (AMOVA) They also refer to a few recent studies [3: Bauchet et al., 5: Tian et al., 6: Seldin et al.]:
revealed that clustering the individuals according to four geographic
groups—north (NO, SE, FI), north-west/central (IE, UK,
DK, NL, DE1, DE2, AT, CH, FR), east (HU, RO, PO, CZ), and
south (PT, ES1, ES2, IT1, IT2, YU, EL)—explained an average
of 0.17% (95% coefficient interval: 0.0% to 0.91%) of the total
genetic variance, whereas individual subpopulation affiliation
explained 0.25% (95% coefficient interval: 0.0% to 1.25%).
Overall, our study showed that the autosomal gene pool in
Europe is comparatively homogeneous but at the same time
revealed that the small genetic differentiation that is present
between subpopulations is characterized by a significant
correlation between genetic and geographic distance. Furthermore,
the qualitative nature of these results is in close agreement
with expectations based on human migration history in
Europe. The major prehistoric waves of human migration in
Europe followed south and southeastern to north and northwestern
directions , including the first Paleolithic settlement
of the continent by anatomically modern humans , most of
the postglacial resettlement during the Mesolithic , and the
farming-related population expansion during the Neolithic [18,
20]. Thus, both the level and the change in neutral autosomal
variation in Europe can be expected to roughly follow southernto-
northern gradients as we observed, with the possible exception
of population isolates as observed for the Finns.
Previous studies based on genome-wide SNP diversityUPDATE (Aug. 13) The Spittoon blogs about this:
reported differences between individuals of southern and
northern/central European ancestry [3, 5, 6] and, to a lesser extent,
between those of eastern and western European ancestry
, which were not confirmed in our study.
They confirm the findings of several recent but smaller European studies (Seldin et al, PLoS Genetics (2006); Bauchet et al, AJHG (2007); Tian et al, PLoS Genetics (2008); Price et al, PLoS Genetics (2008); Paschou et al, PLoS Genetics (2008))This is contradicted by what the authors actually say about three of these studies (see last quote above). The Spittoon also writes:
In the case of this current paper the Finns are the only nationality completely distinct from the rest of the European samples. The Finns speak a different kind of language from much of the rest of Europe, and are the only Scandinavian population represented.Actually, Finland is not usually thought of as a Scandinavian country; even if it is, it is certainly not the only Scandinavian population represented, since all three Scandinavian nations (Norway, Denmark, Sweden) were sampled.
The position of the Finns is likely due to the fact that they share quite recent ancestry with Asians, as evidenced by their possession of Y-chromosome haplogroup N-Tat.
Update (Aug. 14)
It is interesting how these results parallel those of Li et al. (2008), according to which Russians from Vologda have a membership of 86% in the main European cluster, Tuscans have 95%, and all others (except the Adygei from the Caucasus) between 99-100%. Given that Russians have a Finno-Ugrian substratum, these results parallel those of this study in which the two major genetic differences within Europe are primarily because of the Finns, and secondarily because of the Italians.
Update (Aug. 19): A previous study had discovered a substantial overlap between Greek and Italian Americans. Is the disjointness between Greeks and Italians discovered in the newer study the result of a larger number of markers, or due to the fact that northern Greeks and Central Italians seem to have been sampled? As is well known, Greek colonization of Italy originated mostly in the Peloponnese, and occurred in southern Italy and Sicily, and immigrants to America were not drawn uniformly from the territories of Italy and Greece.
Current Biology doi:10.1016/j.cub.2008.07.049
Correlation between Genetic and Geographic Structure in Europe
Oscar Lao et al.
Understanding the genetic structure of the European population is important, not only from a historical perspective, but also for the appropriate design and interpretation of genetic epidemiological studies. Previous population genetic analyses with autosomal markers in Europe either had a wide geographic but narrow genomic coverage  and , or vice versa , ,  and . We therefore investigated Affymetrix GeneChip 500K genotype data from 2,514 individuals belonging to 23 different subpopulations, widely spread over Europe. Although we found only a low level of genetic differentiation between subpopulations, the existing differences were characterized by a strong continent-wide correlation between geographic and genetic distance. Furthermore, mean heterozygosity was larger, and mean linkage disequilibrium smaller, in southern as compared to northern Europe. Both parameters clearly showed a clinal distribution that provided evidence for a spatial continuity of genetic diversity in Europe. Our comprehensive genetic data are thus compatible with expectations based upon European population history, including the hypotheses of a south-north expansion and/or a larger effective population size in southern than in northern Europe. By including the widely used CEPH from Utah (CEU) samples into our analysis, we could show that these individuals represent northern and western Europeans reasonably well, thereby confirming their assumed regional ancestry.