" Within the region of DNA that was apparently undergoing evolution in response to the plague is a family of genes with typically clunky names.* They’re called Toll-like receptors, or TLRs, and the proteins they encode sit on the surface of immune cells such as those hungry macrophages and sentinel cells. There they vigilantly await the advent of microbes with very specific markings. Upon identification of such an invader, an immune klaxon goes off, and the innate army of cells that protect us from within is activated. TLRs 1, 2, 6, and 10 are the combination that recognizes Yersinia pestis, and there they are, as a cluster, sitting right in that zone that has subtly but measurably evolved in Romas and Romanians, but not in the rest of the world. The mark of the plague is in our genes. "

― Adam Rutherford , A Brief History of Everyone Who Ever Lived: The Stories in Our Genes