HOWARD THE DUCK (1986) Condom Scene [HD] Lea Thompson - YouTube
OK, I'm attempting to bring some levity to the topic of evolution. When I was a boy in high school I gave my teachers hell when the topic of evolution was mentioned. I was pretty smart stuff. One of my favorite arguments was against the evolution of internal fertilization, aka, the penis. My brilliance had assumed that there was no way the shift from external to internal fertilization could be explained. There was a clear line between animals that rubbed cloacae and those who had penises. I can laugh about it now.
Anyway, the unique ways animals sexually reproduce is a huge topic, for now I'm focusing on the mallard duck. I'm watching them swim around as I type this. I had mistakenly thought all birds did the cloacal kiss as they call it. The transfer of sperm was a less efficient matter of proximity. However, some years back I learned the far more bizarre facts of life of the duck. Ducks, and for that matter about 3% of bird species, have penises. Do Birds Have Penises? | Bird Reproduction | Bird Spot
The mallard penis is a marvel of biological improbability. The males' penis grows in length in relation to the number of male rivals present. The more rivals, the longer it grows. These penises have been known to be as long as their body! The shape is the weirdest thing. It's a corkscrew. Why a corkscrew? Why are duck penises corkscrew-shaped and how do they mate? | BBC Science Focus Magazine
Ducks' bizarre genitalia is a result of a sexual arms race. Forced mating is common among ducks, so while males' long, flexible penises increase their chances of successfully fertilising a female, the females' anticlockwise vaginas give them a level of control. "Those complex structures prevent full eversion of the penis of unwanted males, so their sperm ends up closer to the cloacal entrance where the females can get rid of it more easily." That is, Brennan's research found that female ducks can prevent fertilisation from unwanted males.
However, if the female wants to mate with a certain male, she can relax her cloacal muscles to allow easier access.
She had better act quickly however as the male penis is lightning fast. Taking less than a third of a second to get full length and unload. Explosive eversion of a duck penis. - YouTube
Modern genetic study has shown that in fact all birds have the genes for penises.
All the genes responsible for growing a penis exist in birds, and they start life inside the egg with something called a genital tubercle. But whereas in mammals this develops into either a penis or a clitoris, for the majority of birds, the tubercle stops growing after just a few days. In birds, apoptosis of the genital tubercle is triggered by a gene called Bone morphogenetic protein 4, or Bmp4, a protein involved in bone, muscle, cartilage, and limb development. In the majority of birds, Bmp4 gets switched on and blocks the genital tubercle from developing into a penis so they either lack one altogether or it’s so small as to be rendered useless.
We have now concluded the common ancestor of dinosaurs, birds and mammals, in fact all amniotes, had something of a penis. Evolution of the Penis | The Scientist Magazine® (the-scientist.com).
Why has this 'reverse' evolution taken place? It seems whether the bird develops a penis is a matter of the timing of the activation of the Bmp4 protein which has adaptive value to the bird's tissue growth. IOW, a consequence of another otherwise valuable adaptation. As most birds have been able to 'get it on' without their penises sufficiently well to continue as species, we have what is called a tradeoff. Something gained effectively equaling something lost.
My 16 year old high school self is putting his hands to his face with embarrassment now.