A barefoot Berkeley boy from the 1960s-70s, he completed his undergraduate work at Cal, majoring in biology with a concentration in marine biology, before unexpectedly moving to the East Coast. There, he spent four years studying South American electric fish and later served as a science writer at Cold Spring Harbor Laboratory on Long Island. He then pursued a PhD in history at Stony Brook University. From 1997 to 2002, he was Assistant, then Associate Professor of History, and Deputy Director of the Center for History of Recent Science at George Washington University. In 2003, he joined the Institute of the History of Medicine at Johns Hopkins, becoming a Full Professor in 2014. During 2015-16, he served as the Kluge Professor of Astrobiology at the Library of Congress and NASA. He is the author of The Tangled Field: Barbara McClintock's Search for the Sources of Genetic Control (Harvard, 2001) and The Science of Human Perfection: How Genes Became the Heart of American Medicine (Yale, 2012). His work has appeared in The Atlantic, The Nation, The New York Times, Nature, Science, and on National Public Radio, among other public outlets. He has also made appearances on NPR and PBS. His current project is a biography of James D. Watson, under contract with Basic Books.