Jewishness is not just in your heart or in your soul, it's also in your genes.
A new study carried out by geneticists in New York and Tel Aviv suggests that Jews have a particular genetic signature.
Geneticist Harry Ostrer, of New York University, said that within specific communities, such as Ashkenazim or Sephardim, Jews are as closely related as fourth or fifth cousins.
Furthermore, Dr Ostrer, lead author of the study titled Abraham's Children in the Genome Era, said all Jews have a common Middle Eastern ancestry.
Meanwhile, our nearest genetic relatives in the non-Jewish world in Europe are Italians and other southern Europeans. In the Middle East it is the Palestinians, Druze and, to a lesser degree, Bedouins.
"I hope this gives new insight into the genetic origins and relatedness of Jews," said Dr Ostrer.
Researchers for the study collected DNA from seven Jewish groups: Iranians, Iraqis, Syrians, Italians, Turks, Greeks, and Ashkenazi Jews.
Subjects had to have four grandparents from the same Jewish community. Their DNA was then compared with each other's and with non-Jewish groups including the Gogodala people of Papua New Guinea, who believe they are descended from the 'lost tribes'
of Israel.
Dr Ostrer said that one of the main findings of the study, which was published in this month's American Journal of Human Genetics, was that European Jews share a common Southern European ancestry that probably predates the Roman Empire.
"I think there was a massive conversion to Judaism during classical antiquity," Dr Ostrer said.
"Judaism was perceived in the Hellenistic world as an intellectual religion and it had great appeal. The Jewish historian Josephus estimated that 10 per cent of the Roman Empire was comprised of Jews. And this empire extended from Asia Minor across the Mediterranean basin."
The study also showed that certain Sephardic Jews are closely related to Ashkenazi Jews, added Dr Ostrer.
He pointed out that Sephardim of Italy, Turkey and Greece have a shared European ancestry with Ashkenazi Jews. Meanwhile, Syrian Jews showed genetic evidence of mixing with Iberian Jews, probably following the Spanish Inquisition.
"There is so much diversity among Jewish groups," Dr Ostrer said. "So this distinction between Ashkenazi and Sephardi Jews is fairly simplistic."
Dr Ostrer said the study disproved theories, such as those raised by Arthur Koestler in The Thirteenth Tribe, that Ashkenazi Jews' roots lie in
Central Asia.
He said it also disproved last year's controversial book The Invention of the Jewish People, by Tel Aviv University professor Shlomo Sand, which claimed the Jews had no common ancestry and there was no such thing as a Jewish nation. Dr Ostrer described the book as "bad genetics".
Dr Ostrer suggested his research might help genetic testing companies offer products that predict Jewish ancestry.
It could also be used to develop new genetic tools to study breast cancer, prostate cancer, inflammatory bowel disease and Parkinson's Disease among Jews.
Dr Ostrer also hopes it might cultivate a greater appreciation of Jewish diversity.
During the recruitment process for the study, Dr Ostrer said Iranian, Iraqi and Syrian Jews in New York expressed grievances against their Ashkenazi neighbours.
"They felt marginalised and unappreciated for their diversity," he said. "It is certainly one of my hopes to cultivate a greater appreciation of various diaspora groups."
A second major study, by 21 geneticists, went so far as to conclude that almost every Jewish community in the world can trace its roots directly back to the Levant, with just two exceptions - the Jews of India and Ethiopia.
Geneticists collected DNA samples from 14 diaspora communities and compared them to the genetic makeup of nearly 70 non-Jewish populations from the same or neighbouring regions.
Tudor Parfitt, professor of Modern Jewish Studies at the School of Oriental and African Studies in London, co-authored the study, which was published in science journal Nature this month.
Prof Parfitt said the findings confirm that the Beta Israel (Falasha) community in Ethiopia did not have Israelite roots.
"It seems certain that their form of Judaism was one which developed in Ethiopia partly for political reasons. Jews did not go to Ethiopia in ancient times - but Judaism did."