COLUMBIA, MISSOURI—Are Paleoindian hunters responsible for the demise of North America’s megafauna? Matthew Boulanger and R. Lee Lyman of the University of Missouri, Columbia, compiled databases of radiocarbon dates of megafauna remains and Paleoindian sites in the northeastern United States. They found that although humans and megafauna coexisted in the region for about 1,000 years, most of the megafauna had already disappeared, after two major periods of decline, by the time that humans moved into the area. Environmental stresses and the climate change of the Younger Dryas period, a 1,300-year-long cold snap beginning 12,700 years ago, could be to blame for the massive extinctions.