Our study of the autosomal STR variation did not support the hypotheses of a recent common ancestor between the Basques and populations either from the Caucasus or North Africa. Allelic dropout was noted for several samples in the present analysis, raising the possibility of a technical or genomic error in the typing of samples. At low sample DNA concentrations, the Profiler Kit is known to preferentially amplify short alleles and homozygotes (93
). Because the samples collected in this study were from buccal swabs, and only a portion of each sample was used for STR analysis, DNA concentrations were much lower than if the samples had been from whole blood. The excess of homozygotes at D8S1179, even after correction for allelic dropout, was of particular concern. Concordance studies of autosomal STR typing across different multiplex kits have reported issues with the D8S1179 locus in certain populations, principally with alleles 15-18 using the Profiler Plus Kit (94
). Reports of D8S1179 from previous studies among Basques give frequency ranges for alleles 15-17 between: 15 (0.110-0.210), 16 (0.010-0.029), and 17 (0.005-0.007) (54
). D8S1179*18 has not been previously reported in Basques. Frequencies for D8S1179 alleles 15-17 in the present study fall within the ranges previously reported for this population (54
), and we also found no individuals with allele 18. In addition, the locus-by-locus AMOVA demonstrated that the Basque provinces were homogeneous with respect to autosomal STR variation, and the single locus found to not be in HWE (D8S1179) did not significantly contribute to differences between provinces. Therefore, we do no believe that the failure to meet HWE in this case represents a technical error, and we included the D8S1179 allele in the interpopulation analyses.
The present analysis of autosomal STR variation does not support either the Caucasian or Vasco-Iberian hypothesis of Basque origins. Caucasian languages themselves are not a cohesive group, and while some linguists see similarities between Basque and some aspects of the northern or southern Caucasian languages, these similarities have been attributed either to poor interpretation, a shared Euro-African substratum, or similarities in the evolution of language itself (11
). Examination of the literature on the Basque-Caucasian hypothesis demonstrates little support from the genetic evidence (6
). Cluster analysis of classical genetic markers showed that subpopulations sampled in Vizcaya were more genetically similar to each other than to other European populations or Caucasian groups outside Europe, such as those in Asia Minor and the Middle East (99
). Comparison of Basque and populations from the Caucasus using 10 blood group and serum protein loci revealed that both non-Indo-European groups were more genetically similar to their neighbors than to each other (6
). Analysis of HLA data showed that the Svani (a Kartvelian-speaking population) and the Basques were found to share only a single five-locus extended haplotype, A*01-B*8-DRB1*03-DQA1*0501-DQB1*0201 (95
). This is the most frequent HLA haplotype found in Europeans (100
), and is present in the Svani at a frequency of 1.25% and among Basques at 2%, leading the authors to conclude that the HLA system does not support the hypothesis of a relationship between these groups.
Recent studies of molecular markers also found little similarity between Basques and populations living in the Caucasus region. Analysis of Y-SNP haplogroups found that FST
values between Basques and Caucasus-dwelling groups were much greater than between Basques and surrounding Indo-European populations (96
). While comparison of mtDNA sequences did reveal greater affinity between European groups and Caucasians than between West Asians and Caucasians (97
), the addition of populations from Iran resulted in a genetic picture in which the Caucasus groups fell between populations from Europe and Asia Minor with respect to mtDNA sequence variation (98
). As with Y-SNPs, genetic distances based on mtDNA sequences were greater between Basques and Caucasians than between Basques and Indo-Europeans, lending credence to the hypothesis of no genetic relationship between Basques and Caucasian populations. The results of the present study agree with those previously published using other genetic markers, as genetic distances based on autosomal data place the Basque groups in a different quadrant of the MDS plot than the population from Georgia.
The Vasco-Iberian hypothesis is based partly on craniometrics, the anthropometry of head shape (102
). Broca suggested, based on a sample of 60 skulls from Guipuzcoa, that the Basques were similar to populations in North Africa (103
). However, a reanalysis of Broca’s sample supplemented by the addition of 19 skulls noted no greater similarity between Basques and North African groups than any other European populations with regards to head shape (105
). A more recent multivariate analysis of 20 craniometric variables in 13 Iberian populations demonstrates the unique position of Basques in the Iberian Peninsula (106
). Regardless of sex, Basques were distinct in every analysis performed. The differences between Basques and other Iberian populations could not be accounted for solely by geographic distance and were instead attributed to greater age of the Basque population relative to the others.
The majority of genetic studies supporting a relationship between Basques and North African populations have been based on HLA data (8
). Other genetic systems do not support a relationship between Basques and North African groups (112
), and additional HLA analyses also found no evidence of a relationship between the two populations (29
). Preliminary investigation of autosomal STRs in Vizcaya Province indicated similarity with the Basque province of Guipuzcoa, and distinction from North African groups in the Maghreb (58
). The present study demonstrates the lack of relationship between Basques and populations of North Africa, as the Basque populations do not cluster near either North African population included in the MDS plot (Morocco and Egypt), but rather are found near neighboring Cantabria. Our results instead lend support to the hypothesis that the Basques are a distinct European population, with no detectable prehistoric connection to (or recent gene flow from) populations in the Caucasus or North Africa.