Haris Lessios holds a Ph.D. from Yale University and is a staff scientist and Acting Deputy Director of the Smithsonian Tropical Research Institute. He studies the mode and tempo of molecular evolution. Using a timeline for the rise of the Isthmus of Panama approximately 3 million years ago, Lessios and colleagues test ideas about the effects of disruptions in gene flow and complete biogeographical isolation on the emergence of new species. Lessios, who is a Fellow of the American Association for the Advancement of Science, organized and edited the proceedings of the 1986 International Coral Reef Congress, held in Panama City. His recent reef research has taken him to the Canary Islands and the Indo Pacific. A member of the STRI staff since 1979, Lessios and colleagues successfully anticipated and were able to document massive (97%) mortality of one sea urchin species, Diadema antillarum, throughout the Caribbean region in 1983.