TC: explain why sexual dimorphism in birds is different from mammals

RP: most birds don't have a penis.

Heard on @tylercowen 's podcast #conversationswithtyler with guest #ornithologist #richardprum at about the 9 minute mark. https://conversationswithtyler.com/episodes/richard-prum/

... the idea being that without a penis there's no mechanism for rape to propagate the species, and instead females get to pick. And they choose beauty. It also allows (causes?) birds to be more monogamous and to have both parents contribute to raising the young.