new study by geneticist Mark Jobling and his colleagues at Leicester University.In order to answer these questions, Jobling and his colleagues performed genetic analyses on 1,140 males from the Iberian Peninsula. They focused on the Y-chromosome DNA, which is passed down from father to son and can be used to trace paternal ancestry. Jobling and his team found a surprisingly large percentage of DNA types that can be traced back to either Jewish (19.8%) or North African Muslim (10.6%) populations.These levels stand in contrast to historical accounts, which emphasize the expulsion of these two minority groups from Spain and Portugal. According to Jobling, “These findings attest to a high level of religious conversion (whether voluntary or enforced) driven by historical episodes of religious intolerance.”The genetic evidence lends support to the idea that most Jews and Muslims preferred conversion to Christianity, as opposed to expulsion from the region. Ultimately, the descendants of those who converted began to integrate into the Christian population. Today, most of these descendants remain unaware of their ancestors’ religious conversion.The conclusions reached by Jobling and his colleagues illustrate how useful genetic analysis can be in assessing the historical record. Since researchers began using genetics to understand the past about two decades ago, they have focused their attention on prehistoric events such as the origin of the human species in Africa, the migration of people into new territories and the expansion of innovations such as agriculture and pottery.But the gradual accumulation of data now allows scientists to tackle more recent and localized events. Just last month, researchers with the National Genographic Project used the genetic diversity of modern populations around the Mediterranean to piece together Phoenician trade routes from nearly 3,500 years ago.This latest study shows that genetic data can actually be used to test historical claims and assumptions, and even to overturn conventional wisdom. In fact, the results of this research actually contradict some historians’ beliefs about the fate of the majority of Jews and Muslims living in the Iberian Peninsula during the Inquisition. Clearly, using genetic data to test hypotheses based on historical or archaeological evidence promises to be surprisingly informative in the future.