In nature, every prey has a predator, every predator has someone who can take it down. That is, I think, why nature requires homosexuality, so that men are not only predators but also, sometimes, prey. For balance. There can be no predator without a weakness in nature, and mens' understanding of what women go through on the part of men is predicated on their ability to be prey. There are only two genders, so you have to turn a gender on itself to get the effect.