And no, it’s not Paul Verhoeven movies. Instead, researchers at Harvard sat down and asked themselves why, precisely, the twig and berries are located where they are. And believe it or not, it’s actually nature recycling some genetic code.
As noted in Nature, when the ancestors of humans crawled out of the primordial muck and got used to this whole “walking” thing, our genitalia migrated. This was for a variety of reasons, not the least of which was that putting your fun bits on your legs is poor design when you use those legs to get around.
It also didn’t help that the cloaca was over said fun bits; pooping on your genitals is not usually considered a fun time. So, as the cloaca moved, the body repurposed the parts it didn’t need anymore, like the tail, and turned them to better use. Essentially, as a fetus, you start growing a tail, and the body realizes “Crap! We don’t need a tail! What should we do?” For men, the answer is “Staple it to the front, run a tube through it, and call it a day.”
This is common practice across species; before a snake gets a trouser snake, this study found, it starts growing some legs. Basically every penis is like that work project where you get started and then it suddenly turns into something else entirely.
Now, as to why nature put the single most painful place to get kicked right at the ideal place for somebody to kick it… researchers are still stumped. That one will probably remain a mystery for the ages. But at least we know how it got there!