Nature may need to make only a small number of genetic changes tocreate a new species, according to H. Allen Orr, a postdoctoral researcher with the Center for Population Biology at UC Davis. Most previous scientists -- including Charles Darwin -- had believed that the origin of species involved the slow accumulation of many genetic differences. Recent work by Orr and others has uncovered some surprises. Orr genetically analyzes the offspring of closely related species of the fruit fly, Drosophila, which often display the sterility and inviability associated with the early stages of speciation. "It's beginning to look like hybrid sterility has a simple genetic basis," he says. Orr will review the genetics of speciation and discuss his research at the Molecular Genetics and Evolution symposia at the annual meeting of the American Association for the Advancement of Science in Chicago next week. Embargoed until 2:30 p.m., Saturday, Feb. 8.