According to David Goldstein, a Duke University geneticist and a key researcher in population studies, most of the male founders of European Jewry were probably Jewish traders or money lenders who came to the area without spouses. ey mixed with local pagans and probably saw an infusion of some Khazarian royalty when the empire crumbled.

Based on male and female DNA evidence, over the past 1,000 years or so, the Jews and gentiles that made up the founding families of Ashkenazi Jewry adopted a very strong Jewish identity. ey remained ercely insular and married within their community. Conversion, while allowed, was dif- cult.

e closed nature of their society has le a deep genetic footprint. University of Arizona geneticist and Y-chromosomal expert Michael Hammer estimates that the rate of non-Jews who entered the European Jewish gene pool over the past centuries was less than 0.5 percent per generation, at least until recent decades. As a result, Ashkenazim are considered one of the world’s most distinctive populations (a term scientists use rather than the folkloric notion of “race”). at’s made them a favorite of population geneticists—and a gold mine of data for DNA testing companies. It also helps explain why there are more than 40 diseases that are common to Jews and why major testing companies are beginning to roll out “ethnic panels” that focus on the behavioral and disease idiosyncrasies of distinctive populations.

DNA is at once an atlas and time machine that can transport us to Biblical times and beyond, awakening us to the shared roots of civilization

and the promise of designer therapies to target disease. We are on the verge of expanding this tracking process beyond our male and female lineages to the entire human genome, which would give us a far more complete picture of the ethnic threads woven by nature to create each of us. e great paradox of human biodiversity research is that the only way to understand how similar humans are is to learn how we di er. at includes me.

A er my sister’s diagnosis, I had myself tested and was found to carry the same mutation that my sister carries. Its e ects on men include a slight risk of breast cancer and an increased possibility of melanoma of the eye. But more frightening, my daughter, who is a product of a mixed Christian-Jew-ish marriage, has a 50/50 chance of carrying this gene fault; if she does, the probability that she will eventually contract cancer is estimated to be as high as 80 percent.

It wasn’t surprising that in its end-of-the-year issue, Science magazine named “human genetic variation” ( www.sciencemag.org/cgi/content/ full/sci;318/5858/1842) as the scien- ti c breakthrough of 2007—we each carry pinpoints of DNA that suggest that maybe human population groups aren’t really quite so alike. However slight our genetic di erences may be, they are de ning. ey contain the map of our family trees back to the rst modern humans. ey catalog our vulnerability for many diseases. And they mark me indelibly as a Jew.

is author of Abraham’s Children: Race, Identity and the DNA of the Chosen People (www. abrahamschildren.net), and can be contacted via his website, < www. jonentine.com>.