Enlarge Image Family ties. Most Jewish populations share a genetic connection, but some groups, such as Ethiopian Jews (pictured here, sharing unleavened bread ahead of Passover), stand alone. Credit: Eliana Aponte/Reuters Scholars of all kinds have long debated one seemingly simple question: What is "Jewishness?" Is it defined by genetics, culture, or religion? Recent findings have revealed genetic ties that suggest a biological basis for Jewishness, but this research didn’t include data from North African, Ethiopian, or other Jewish communities. Now a new study fills in the genetic map—and paints a more complex picture of what it means to...