Evolution on a massive scale


For the first time, scientists have measured how fast large-scale evolution can occur in mammals, showing it takes 24 million generations for a mouse-sized animal to evolve to the size of an elephant. Research published in the Proceedings of the National Academy of Sciences describes increases and decreases in mammal size following the extinction of dinosaurs 65 million years ago. An international team of 20 researchers, including Odum School of Ecology Dean John Gittleman and Assistant Research Scientist Patrick Stephens, discovered that size decrease rates are much faster than growth rates. It takes only 100,000 generations for very large decreases, leading to dwarfism, to occur. Most previous work has focused on microevolution, the small changes that occur within a species. The paper looked at 28 different groups of mammals, including elephants, primates and whales, from various continents and ocean basins over the past 70 million years. The research furthers understanding of conditions that allow certain mammals to thrive and grow bigger and circumstances that slow the pace of increase and potentially contribute to extinction.