Charles Darwin has gone down in history for writing On the Origin of Species , but that wasn't his only contribution to our understanding of the natural world. His last manuscript could just as well have been called On the Origin of Feces . In his final working years, the co-discoverer of evolution became downright enamored with worm poop. He made detailed descriptions of how worm poop coiled into tower-like spirals . In November 1880, Darwin wrote to a friend: "My whole soul is absorbed with