The human penis is extremely unique in nature.
Nearly all animals that have penises, have bones in them, even chimpanzees. Humans do not because we walk upright. It would be impossible for men to function safely if they were walking, running, hunting, or even bending over if they had penile bones. Instead, our penis works hydraulically. In order for it work at all, sexual arousal has to take place. For penetration to occur, the penis must be stimulated to do so. Our boneless penis is much larger in proportion to our bodies because it is boneless and because the human vagina is comparatively larger to accomodate our comparatively large infants.
Biologists have theorized that if humans never took to walking upright, not only would our penises be much smaller, but we wouldn't derive sexual pleasure from them OR from the clitoris because there would be no need for sex to be pleasurable. Like animals, we would mate out of instinctual need, not desire.
There are many unique things about humans but our sexual organs are particularly brilliant and fascinating; unique in all the world for being capable of giving us intense physical pleasure.
So while the penis may look a bit odd or even silly, it's an ingenious bit of nature's engineering. Without it, men and women would not find joy in sex.