Since you're having an educated chat about this and making a strong point. I would be interested to see what you could find. I have never run across it in any art history or tribal art but I also was not seeking that subject matter. If anyone indulged in bodily pleasures more than anyone it was the greeks and romans. the coliseum events had some pretty insane sexual slave shows. frightening. Thanks
Prostate is male orgasm button. It crates more intense pleasure than penile stimulation and all men need to get their balls drained like that. We have to restrain our subjects during prostate milking procedures because their intense twitching and shaking which could interfere with the procedure. And you cant look at it evolutionary because from what we know about the world today there might be ancient civilizations and times where humans were milked like we milk bulls today.