What came first: rattle or shake?

摘要

Shake, rattle and strike. It is one of the most terrifying sounds in the animal kingdom, but how the rattlesnake evolved its chilling warning signal is a mystery. The evolution of the rattle has baffled scientists because, unlike other complex physical traits like eyes or feathers, it has no obvious precursor or intermediate stage. "There is no half-rattle," says David Pfennig at the University of North Carolina at Chapel Hill.