A gene that is active in humans today died out during our primate evolution and came back to life again. This is the first time such a "resurrection" event has been identified, researchers say.The family of genes known as IRGs are essential to mouse immunity. Without the genes, for instance, a mouse exposed to salmonella will die within a couple of days. Humans, however, only have one gene from this family, IRGM, and Cemalettin Bekpen, at the University of Washington in Seattle, wanted to know why.