Snips and snails and puppy dogs’ tails, or sugar and spice and all things nice? From our animal-centered point of view, the distinction between males and female can seem rather obvious—many animals have male individuals and female individuals whose differences are often pretty evident at a glance. However, we’re also aware of more exotic variations like hermaphroditism and Tiresias-like midlife gender-bending. Indeed, the further we get from the birds and the bees, the more it becomes unclear what exactly we mean by “male” and “female.” Are these just tags, or are they fundamentally different? And if the latter, how did this fundamental difference come to be?