Evolution loves penises. How else do you explain all the crazy penis shapes out there? Por ejemplo (slightly nsfw): the corkscrew duck penis, the spiny cat and chimp members, the sci-fi-esque spiked penis of a seed beetle, the 4-headed penis of the echidna, and, well, all of these.
Why so many ways to make a sperm delivery system?
The shape, size, and WTF-ness of penises in part depends on the mating system it’s a part of. For example, Muscovy ducks have crazy long, corkscrew-shaped penises, possibly because they’re part of a very competitive mating system. Males and females form tight pair-bonds, but this doesn’t stop rival males from trying to get in on the gene-spreading action. Males will often forcibly copulate with females, and the longer and twistier their penis, the more likely they’ll be able to get their sperm closer to the eggs.
But female ducks evolved countermeasures. Their genital tracts became twisted, too (in the opposite direction) to make it more difficult for a male to force his way in. And on it goes.
Other animals can get away with having penises that physically harm the female. Examples include bed bugs and seed beetles. It actually works out in the male’s favor to induce harm, because the female will have less lifespan to mate with other males. There’s no pressure from the female side to select for less knife-like dongs, because they end up having a crapload of babies anyway.
Basically, there are a zillion different ways of having sex and making babies. And there’s a special penis shape for each and every one.
Lock and key
Okay, so evolution can push penis shapes to crazy extremes–and it does so ridiculously quickly–but of course there must be limits. The key still has to fit the lock, so to speak. So, as penis shapes evolve in one direction, lady parts follow, as long as these new shapes are beneficial. But not every member of a species will mate with every other member of the species. Especially if there are pockets of this species that are isolated from one another.
What would happen if two populations, that were isolated for a long time, came together and, um, didn’t fit anymore? Could this be the driving force for making two species out of one? Researchers Janine Wojcieszek and Leigh Simmons at Murdoch University in Australia used millipedes to answer this question. Continue reading