Poison frogs become poisonous by isolating chemicals from their food and storing them in their skin. One such compound, epibatidine, is a stronger painkiller than morphine, but has not been tested in humans because even low doses are deadly to rodents. But for the frogs themselves, this powerful neurotoxin is totally impotent.Another open question centers on the order in which these mutations arose, says UVA evolutionary biologist Edmund Brodie III, who was not involved in the work. “It’s a reasonable conclusion that frogs evolved this resistance first and then [made] compensatory changes afte...