A scientist trying to understand why Argentine lake ducks have foot-long spiral-shaped penises discovered that duck vaginas, which often have pockets and cul-de-sacs, spiral in the opposite direction; a comparison of sixteen duck species also revealed that as vaginas become longer and more complex, males evolve longer penises.
A scientist trying to understand why Argentine lake ducks have foot-long spiral-shaped penises discovered that duck vaginas, which often have pockets and cul-de-sacs, spiral in the opposite direction; a comparison of sixteen duck species also revealed that as vaginas become longer and more complex, males evolve longer penises.