Just in from Rueters...
Three: Why roosters are the worst animal to share a nickname with the penis.
Don’t be fooled by his strut. He may look, well, cocky but between his chicken legs the rooster has nothing but an opening. He engages in sex by lining up this opening with the analogous one on the hen, sending sperm from his cloaca to hers. Chickens have nothing to be too ashamed of, since 97% of birds are penis-less. But how did this situation come about? Since mammals and reptiles have external genitalia, it seems likely the ancestors of birds had them. Florida’s Cohn solved the chicken puzzle last year.
He found that birds develop a genital tubercle – the proto-penis/clitoris, just as we mammals do, but for most birds it degenerates later in the animal’s development. It’s hard to say exactly why this happened, but evolution sometimes disposes of things that aren’t necessary, and chickens and other birds seem to be able to fertilize eggs make baby birds without any external genitalia.
Another oddity about birds is that among the 3% with penises, many are extravagant. Duck penises are not only long but often shaped like corkscrews. The most egregious case is the Argentine lake duck, whose 15 inch penis is longer than the rest of the bird. This anatomical quirk seems to have evolved in an evolutionary arms race with female ducks.
Scientists investigating this phallalogical mystery found that the length and corkscrew shape appears to be a counter-strategy to an interesting feature in the female. Female ducks often have twisted vaginas with pockets and cul-de-sacs that don’t lead to the oviduct, possibly allowing them to avoid being fertilized by undesirable males.