Studying two very particular ethnic groups: from Pygmies to Basques
Pygmies, everyone knows, present the lowest height among humans – adult men grow to less than 150 cm. One can find pygmy populations not only in Africa, but also in Australia, Brazil and several countries in Asia. The fact that populations in such diverse locations all have short stature in common suggests the presence of strong selective pressures on this phenotype, but this has never been proved. David Comas and colleagues from the Institute of Evolutionary Biology (IBE: CSIC-UPF) have recently published in the journal Human Genetics the first genetic hint of adaptive evolution in the African Pygmy phenotype.
They have developed a novel approach to survey the genetic architecture of phenotypes, one in which the genetic analysis also incorporated environmental variables to understand local adaptation. They have applied it to study the genomic covariation between allele frequencies and height measurements among Pygmy and non-Pygmy populations. The results show that the genomic regions that most likely participate in the genetic architecture of the phenotype, are those associated to bone homeostasis and skeletal remodeling, which could therefore be a key biological process underlying the Pygmy phenotype. They have also proved that these regions have most likely evolved under positive selection. These results are consistent with the independent emergence of the Pygmy height in other continents with similar environments, and support the putative adaptive role of the short stature of Pigmies.
David Comas’ group on Human Genome Diversity has also recently studied another very particular ethnic group, that from the Basque country in Spain. The Basque people have received considerable attention from anthropologists, geneticists and linguists during the last century due to the singularity of their language and to other cultural and biological characteristics. But any attempt to address the questions of their origin, uniqueness and heterogeneity has suffered from a weak study-design where populations were not analyzed in an adequate geographic and population context. In their last paper, published in Molecular Biology and Evolution, the group has tried to solve that by analyzing the Y chromosome and mitochondrial DNA of ∼900 individuals from 18 populations, including some where Basque is currently spoken and others where Basque might have been spoken in historical times.
The results indicate that Basque-speaking populations are similar to geographically surrounding non-Basque populations, and that their genetic uniqueness is based on a lower amount of external influences compared to other Iberians and French populations. The rough overlap of the pre-Roman tribe location and the current dialect limits supports the notion that the environmental diversity in the region has played a recurrent role in cultural differentiation at different time periods.
Mendizabal I, Marigorta UM, Lao O, Comas D. Adaptive evolution of loci covarying with the human African Pygmy phenotype. Hum Genet. 2012 Mar 11
Martínez-Cruz B, Harmant C, Platt DE, Haak W, Manry J, Ramos-Luis E, Soria-Hernanz DF, Bauduer F, Salaberria J, Oyharçabal B, Quintana-Murci L, Comas D, the Genographic Consortium. Evidence of pre-Roman tribal genetic structure in Basques from uniparentally inherited markers. Mol Biol Evol. 2012 Mar 12;