For populations of the Jewish diaspora, the genetic composition of Ashkenazi, Sephardi, and Mizrahi Jewish populations show significant amounts of shared Middle Eastern ancestry According to Behar and colleagues (2010), this is "consistent with an historical formulation of the Jewish people as descending from ancient Hebrew and Israelites of the Levant" and "the dispersion of the people of ancient Israel throughout the Old World" Jews living in the North African, Italian, and Iberian regions show variable frequencies of admixture with the historical non-Jewish host population along the maternal lines.
In the case of Ashkenazi and Sephardi Jews (in particular Moroccan Jews), who are closely related, the source of non-Jewish admixture is mainly southern European.
A study conducted in 2013 found no evidence of a Khazar origin for Ashkenazi Jews and suggested that "Ashkenazi Jews share the greatest genetic ancestry with other Jewish populations, and among non-Jewish populations, with groups from Europe and the Middle East.
No particular similarity of Ashkenazi Jews with populations from the Caucasus is evident, particularly with the populations that most closely represent the Khazar region. Pirooznia, Elhaik advanced the view that the first Ashkenazi populations to speak the Yiddish language came from areas near four villages in Eastern Turkey along the Silk Road whose names derived from the word "Ashkenaz", arguing that Iranian, Greek, Turkish, and Slav populations converted on that travel route before moving to Khazaria, where a small-scale conversion took place.
Recent studies have been conducted on a large number of genes homologous chromosomes or autosomes (all chromosomes except chromosomes X and Y).
A 2009 study was able to genetically identify individuals with full or partial Ashkenazi Jewish ancestry. Harry Ostrer in his book Legacy: A Genetic History of the Jewish People, summarized his and other work in genetics of the last 20 years, and concluded that all major Jewish groups share a common Middle Eastern origin.
Thomas from Research Department of Genetics, Evolution and Environment, University College London, UK, Valentina Fedchenko from Saint Petersburg State University, and George Starostin from Russian State University for the Humanities, dismissed both the genetic and linguistic components of Elhaik et al.
study arguing that "GPS is a provenancing tool suited to inferring the geographic region where a modern and recently unadmixed genome is most likely to arise, but is hardly suitable for admixed populations and for tracing ancestry up to 1000 years before present, as its authors have previously claimed.
These studies investigate the origins of various Jewish populations today.
Citing autosomal DNA studies, Nicholas Wade estimates that "Ashkenazic and Sephardic Jews have roughly 30 percent European ancestry, with most of the rest from the Middle East." He further noticed that "The two communities seem very similar to each other genetically, which is unexpected because they have been separated for so long." Concerning this relationship he points to Atzmon's conclusions that "the shared genetic elements suggest that members of any Jewish community are related to one another as closely as are fourth or fifth cousins in a large population, which is about 10 times higher than the relationship between two people chosen at random off the streets of New York City" Concerning North African Jews, autosomal genetic analysis in 2012 revealed that North African Jews are genetically close to European Jews.
This finding "shows that North African Jews date to biblical-era Israel, and are not largely the descendants of natives who converted to Judaism," Y DNA studies examine various paternal lineages of modern Jewish populations.
Linguistic evidence, however, does not support the theory that Yiddish is a Slavic language, and textual sources belie the thesis that the name Ashkenaz was brought to Eastern Europe directly from a region in the Near East.
Although the focus and methods of research may be different in the humanities and the sciences, scholars should try to account for all evidence and observations, regardless of the field of research.
Behar and colleagues have remarked on an especially close relationship between Ashkenazi Jews and modern Italians, particularly Tuscans.