Charles Darwin saw the history of languages as a model for "descent with modification" in biological evolution; and researchers from Thomas Jefferson to Luigi Luca Cavalli-Sforza and beyond have been excited about the idea of combining linguistic, biological, and geographical evidence to shed light on the history of human populations.
Most recent linguists and anthropologists who are knowledgeable about such topics have been skeptical about how close we should expect linguistic and biological descent to be, in general. There are many ways, both wholesale and retail, for people to end up speaking a language different from the language of their ancestors, and similarly many ways for genes to flow from one speech community to another.
A recent contribution to the skeptical side of the discussion is Hafid Laayouni et al., "A genome-wide survey does not show the genetic distinctiveness of Basques", Human Genetics, published online 1/16/2010.
Here's their abstract:
Basques are a cultural isolate, and, according to mainly allele frequencies of classical polymorphisms, also a genetic isolate. We investigated the differentiation of Spanish Basques from the rest of Iberian populations by means of a dense, genome-wide SNP array. We found that FST distances between Spanish Basques and other populations were similar to those between pairs of non-Basque populations. The same result is found in a PCA of individuals, showing a general distinction between Iberians and other South Europeans independently of being Basques. Pathogen-mediated natural selection may be responsible for the high differentiation previously reported for Basques at very specific genes such as ABO, RH, and HLA. Thus, Basques cannot be considered a genetic outlier under a general genome scope and interpretations on their origin may have to be revised.
There's an excellent discussion of the article by Razib Khan, "The Basques may not be who we think they are", Gene Expression 2/18/2010.
(I believe that "FST" is a form of Wright's coefficient of relatedness — see e.g. Hilde M. Wilkinson-Herbots, "Coalescence Times and FST Values in Subdivided Populations with Symmetric Structure", Advances in Applied Probability 35(3) 2003. I guess I should point out that the analysis in the Laayouni paper is based on a linear (SVD) decomposition of (a relatedness measure derived from) a large (~280k) number of SNP frequencies. I don't know enough about the methods and the assumptions behind them to evaluate how strong an argument their results constitute against "the genetic distinctiveness of Basques" — I suspect that the phrase chosen in their title, "…does not show the genetic distinctiveness of Basques", is a fair way to put it.)
For some general linguistic background, see Don Ringe, "The linguistic diversity of aboriginal Europe", 1/6/2009.