After receiving his B.A. from the University of Chicago in 1978, he entered the M.D./Ph.D. program at the University of California, San Diego. After obtaining both degrees in 1984, he undertook a medical internship at Mercy Hospital, then returned to the laboratory to pursue postdoctoral research at the Salk Institute. He joined the Scripps faculty in 1989. His current research involves the development of directed molecular evolution techniques and their application to the analysis and design of RNA enzymes.