Lynn Margulis is Distinguished University Professor in the Department of Geosciences at the University of Massachusetts, Amherst. She was elected to the National Academy of Sciences in 1983 and received from William J. Clinton the Presidential Medal of Science in 1999. Her publications, spanning a wide range of scientific topics, include original contributions to cell biology and microbial evolution. Best known for her theory of symbiogenesis, which challenges central tenets of neo-Darwinism by asserting that variation in evolution, is largely driven not only by random mutation but by the production of new genomes from symbiotic associations between different organisms. She is also cited for her contribution to the Gaia hypothesis, the theory that the Earth and its living beings function as a self-regulating system. Professor Margulis is the author of many articles and books, the most recent of which are Symbiotic Planet: A New Look at Evolution (1998) and Acquiring Genomes: The Theory of the Origin of the Species (2002), co-written with Dorion Sagan. Indeed, over the past decade and a half, Professor Margulis has co-written a number of books with Sagan, among them What is Sex (1997), What is Life? (1995), Mystery Dance: On The Evolution Of Human Sexuality (1991), Microcosmos: Four Billion Years Of Evolution From Our Microbial Ancestors (1986), and Origins Of Sex: Three Billion Years Of Genetic Recombination (1986).