One of the most fascinating uses of genomic sequence is as a historical chronicle. It's not an easy read, but contained within the genome is information about the ancestors and events that make up any organism's past. As recounted by Harry Ostrer in his Perspective this month on the genetics of Jewish populations, genomic data can complement anthropological data to provide valuable insight into the origins and patterns of migration of the Jewish people, as well as into the genetic basis of Mendelian disorders in Jewish groups. Uncertainties can sometimes be resolved as well. For example, the Lemba — a black South African tribe — have long-standing Jewish cultural traditions. The basis of their claims of Jewish ancestry was finally resolved when an analysis of their Y-chromosomal haplotypes showed that Lemba males were probably descended from a Jewish priestly caste. So oral traditions concerning a group's origin can be good indicators of genetic ancestry. Another important outcome of human population genetics is that it can improve our understanding of the demographics of genetic disease. In turn, this can be used to focus effort on particular populations to improve their health. A good example is provided by Tay–Sachs disease, which is particularly prevalent in Ashkenazi Jews. The incidence of this devastating disease, which causes affected children to die at ∼2 years of age, was reduced — between 1970 and 1992 — from 40–50 deaths per year worldwide to 4–5, as a response to genetic counselling, heterozygote screening and carrier testing in this group. And these benefits are not limited to one population. A better understanding of population history will have a positive impact on human health as a whole, because it is also likely to enhance efforts to uncover the genetics of more common diseases.