Originally Posted by d4m10n
Yes, evidence suggests that every therian mammal that has ever reproduced has done so either by producing one of those two gamete types. Sex seems to be the preferred method of reproduction over parthenogenesis due to its conferring novel genetic combinations. In fact, mammals have evolved differential epigenetic marking of some genes in the two gametes (resulting in their silencing) that precludes parthenogenesis. Meaning you need one of each gametes type for normal development.
ETA- the pseudo-penis of spotted hyena (Crocuta crocuta) females is the classic example of what you're saying.
& it should take a new gamete type/reproductive role to convince anyone that their is another sex besides female & male.