Duck penises show arms race between sexes | Oddly Enough | Reuters
"Interestingly, the male phallus is also a spiral, but it twists in the opposite, counterclockwise, direction," said Yale ornithologist Richard Prum in a statement.
"You can envision an evolutionary scenario that, as the male phallus increases in size, the female creates more barriers. You get this evolutionary arms race," Brennan said.
