Evolution is often thought of as a gradual remodeling of the genome, the genetic blueprints for building an organism. But in some instance it might be more appropriate to call it an overhaul. Over the past 100 million years, the human lineage has lost one-fifth of its DNA, while an even greater amount was added, report scientists at the University of Utah School of Medicine. Until now, the extent to which our genome has expanded and contracted had been underappreciated, masked by its relatively constant size over evolutionary time.