In the late 12th century, at least 17 bodies were dumped down a well in medieval Norwich, eastern England – and that is the end of the certainty. In August, a study published in the peer-reviewed journal Current Biology by Selina Brace of London’s Natural History Museum and colleagues tentatively identified the bodies as Ashkenazi Jews. They had been murdered in a pogrom on February 6, 1190, the authors suggested, based partly on genetics and partly on a “historically attested episode of antisemitic violence” in the city that day. Technically, the paper’s focus was on hereditary diseases associated with Ashkenazi...