My guess is that the only thing that changes is the way we view our sexual practices..."porn" is really a modern concept, mostly born out of Victorian times, the paintings that OF referred to were not so much for erotic stimuation as they were billboards in the brothels of the day, a "menu" of services availible to their clientel...I would expect that cave men & women experimented with every variation of inserting whatever appendange into whatever opening or crevice till they found the ones they liked the most, & it was only later that the priests came along to tell them which ones were unacceptable in the eyes of the dieties...

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