Does this count?

Reproduction takes a high level of energy from the female, but relativelu little from the male. It's in the male's best interest as far as reproduction goes to impregnate as many females as possible, meanwhile due to the relatively high cost for the female it's more beneficial to find a mate who will stay with the female and help ensure their offspring survive. Because of this females will develop reproductive organs which require full co-operation from the female in order to mate. This in turn can result in many different evolutionary responses from males, however the response ducks evolved down is to develop genitals which are better at rape, causing females to develop more counter measures ultimately creating an arms race of strange genitals.

/r/SapphoAndHerFriend Thread Parent Link - i.redd.it