The origins of the Basque people have been the subject of much debate and research.
Using modern DNA sequencing techniques, geneticists have found that Basques have mitochondrial DNA that closely resembles that of the typical Western European, but are genetically distinctive in some ways.
Some of the findings are evidence that the contemporary Basques share genetic characteristics with settlers in the Basque country before the arrival of Indo-Europeans.
However, besides these modern investigations using DNA sequencing, genetic distinctions between the Basques and surrounding people were already noted much earlier.
A striking difference between the Basque people and the surrounding Western Europeans is the high proportion of Basques with Rhesus-negative blood type. In fact, about 16% of Europeans have Rhesus-negative blood (which is more than most populations in the world). Among the Basque, however, some 30-35% have a Rhesus-negative blood type. In no other population is this number so high.
[Doron M. Behar et al., The Genographic Consortium, The Basque Paradigm: Genetic Evidence of a Maternal Continuity in the Franco-Cantabrian Region since Pre-Neolithic Times, The American Journal of Human Genetics, Volume 90, Issue 3, 9 March 2012, Pages 486-493, ISSN 0002-9297, http://dx.doi.org/10.1016/j.ajhg.2012.01.002]