In the two decades since the AIDS pandemic began, one critically important question has never been satisfactorily answered: How did the human immunodeficiency virus (HIV) that causes the disease first infect people? Understanding how the virus emerged and spread could help prevent future pandemics of diseases as yet unknown. After leading the School through 15 years of dramatic growth, Dean Alfred Sommer will step down from his position in September 2005 to return to his nutrition and health policy research. William Eaton remembers that the letter came seemingly out of the blue. It was from Curtis Dohan, a Philadelphia internist specializing in celiac disease, who had noticed that among his patients who also had schizophrenia, curing the celiac disease also seemed to cure the mental illness as well. Robert Blum, Sir George Alleyne, Rita R. Colwell, and Duff Gillespie have all recently joined the School's faculty. | 
