Around 13,000 years ago, the world's climate began to change. Seas rose, glaciers retreated and ecosystems began to transform. At roughly the same time, humans arrived in North America, perhaps attracted by migrating game or newly hospitable land. Over the course of the next few millennia a host of indigenous large-bodied mammals, such as the mammoth, died out. Scientists have long debated whether climate warming or human hunting brought about this megafauna extinction. New radiocarbon dating results support the environmental explanation ... Scientific American