Peter H. Raven (NAS) is the Engelmann professor of botany at Washington University and director of the Missouri Botanical Garden in St. Louis. He is a conservationist who has transformed the Missouri Botanical Garden into one of the world’s leading plant conservation centers. His primary research interests are the systematics, evolution, and biogeography of the plant family Onagraceae, which includes 16 genera and some 650 species. This family of plants has provided powerful models for understanding patterns and processes in plant evolution in general. Another particular interest is plant biogeography — the evolutionary history of entire biota and the individual taxa found in certain regions — and the ways in which these organisms have been influenced by continental movements. He has focused much of his attention on what he considers the menace of a “sixth extinction” — a potential mass extinction of living organisms that would be brought about by the mushrooming human population and by human carelessness and commerce.

Raven’s service to national and international organizations has included president of the American Association for the Advancement of Science, member of the Pontifical Academy of Science, home secretary of the U.S. National Academy of Sciences, member of the President’s Committee of Advisors on Science and Technology, and chairman of the National Geographic Society’s Committee for Research and Exploration. He has received Guggenheim and MacArthur Foundation fellowships. Time magazine, in its 1999 Earth Day issue, declared that Raven is one of its “Heroes of the Planet” for what he is doing “to preserve and protect the environment.”

Barbara A. Schaal (NAS) is the Spencer T. Olin professor of biology at Washington University, St. Louis. Her investigations have focused on the genetic heterogeneity of plant species, including those native to the United States, tropical crops and their wild relatives, and the family of plants called Arabidopsis. She uses a variety of molecular markers in several plant species to study fundamental evolutionary processes, such as gene migration, molecular evolution, and natural selection. Her application of DNA analysis to plant evolution at the population level has revealed unexpectedly high levels of diversity, has led to the development of DNA fingerprinting in plants, and has helped explain the reasons for this level of diversity. She has been involved with work that has identified the wild progenitor of cassava and the probable geographical location of its domestication in the Amazon region of Brazil. She has also examined the evolutionary origins of invasive plants that encroach on wetlands in the western United States. Her recent work has examined gene flow between genetically modified rice and wild relatives of rice.

Schaal currently serves as the vice president of the National Academy of Sciences. She has also been president of the Society for the Study of Evolution and the Botanical Society of America.

Neil deGrasse Tyson is the Frederick P. Rose director of the Hayden Planetarium at the American Museum of Natural History. His research interests include star formation, exploding stars, dwarf galaxies, and the structure of the Milky Way.

Tyson has served on presidential commissions that studied the future of the U.S. aerospace industry (2001) and the implementation of the U.S. space exploration policy (2004). A winner of the Public Service Medal of the National Aeronautics and Space Administration, the highest award given to a non–civil servant, Tyson currently serves on NASA’s advisory council.

In addition to his professional publications, Tyson also writes for the public. He is an essayist for Natural History magazine and the author of The Sky Is Not the Limit: Adventures of an Urban Astrophysicist and Origins: Fourteen Billion Years of Cosmic Evolution, cowritten with Donald Goldsmith. He serves as the host and executive editor for the PBS-NOVA program “NOVA Science Now,” in which each episode profiles the frontier of scientific discovery drawn from such fields as chemistry, biology, geology, physics, robotics, and astrophysics.

Tyson is the recipient of eight honorary doctoral degrees and currently serves as president of the Planetary Society. His contributions to public appreciation of the cosmos have recently been recognized by the International Astronomical Union in their official naming of the asteroid “13123 Tyson.”

Holly A. Wichman is professor of biological sciences at the University of Idaho and cofounder of the interdisciplinary Initiative for Bioinformatics and Evolutionary Studies. She teaches courses in genetics, experimental biology, and professional development for graduate students. Her research focuses on genome organization in mammals and on experimental evolution using viruses as a model system. Her work on mammalian retrotransposons is carried out in a strong phylogenetic framework; she has examined retrotransposon evolution in monotremes, marsupials, and all 18 orders of placental mammals. This work focuses primarily on events that occurred tens of millions of years ago. However, short-term evolution of organisms with generation times that are short relative to that of humans can be observed in real time, both in the laboratory

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