I once went to some cave with some ancient American Indian painting on it when I was in the Boy Scouts.
Some looked like dicks, and I joked with my Troop that I wonder if this "ancient sacred artifact sites" were actually just Paleo-Indian teenagers drawing dicks and asses on the cave walls while bored one night.
I think my theory still holds.
"Teenagers be getting bored and doing shenanigans" is probably one of the safer and less harmful assumptions about human society throughout history.