Scientists have long thought that snakes developed their slender, limbless form because of disrupted Hox genes, a set of genetic blueprints that help establish the body plans of vertebrates. Changes in Hox expression are thought to be a main mechanism driving the evolution of new body forms. In mice and men, Hox genes establish where our necks, trunks, lumbar, sacrum and tail regions go, along a head-to-tail axis. Since snakes don't have most of these distinct areas, it was thought that Hox genes were disrupted in a snake ancestor, resulting in their simplified form as compared to their four-legged lizard ancestors. Scientists from the University of Nebraska-Lincoln and Indiana University turned this theory upside down in a new paper published this month in Nature.