New York Times: The variations in the course Earth travels around the Sun and in the tilt of its axis are associated with episodes of global cooling. New research reported in Nature on the fossil record shows that the cyclical pattern of these phenomena corresponds to species turnover in rodents and probably other mammal groups as well. This effect provides "a crucial missing piece in the puzzle of mammal species- and genus- level evolution," and "offers a plausible explanation for the characteristic duration of more or less 2.5 million years of the mean species life span in mammals."