>Penis goes in, life comes out. You can't explain that. Well, paleolithic man couldn't. But they could draw/sculpt it and revere it

It was not until 1677 [1] that people started to discover how reproduction works beyond "penis goes in, life comes out". Yet there are no major religions documented before that (in about 5000 years of recorded history) which revered crude vulva drawings. Whereas pornographic graffiti has been widespread everywhere from the streets of Ancient Rome [2] to modern boys' bathrooms.

[1]http://en.wikipedia.org/wiki/Antonie_van_Leeuwenhoek#Discove...

[2]http://www.pompeiana.org/resources/ancient/graffiti%20from%2...