Mark W. Denny is John and Jean DeNault Professor of Marine Science in the Biological Studies Department at Stanford University. He is author of "Air and Water: The Physics of Life s Media", "Species Invasions: Insights into Ecology, Evolution, and Biogeogaphy, " and "Biology and the Mechanics of the Wave-Swept Environment." Steven D. Gaines is Director of the Marine Science Institute at the University of California, Santa Barbara and coedited Marine Community Ecology. Together, Denny and Gaines coauthored "Chance in Biology: Using Probability to Explore Nature."