That's like saying humans have evolved radically different behavior compared to 200 years ago because back then they couldn't travel to another celestial body.
I would argue jerking off to Internet porn and jerking off to a fantasy are both exhibiting the same behavior, just like a polar explorer from the 19th century and a lunar explorer from the 20th century are exhibiting the same behavior.
We have very little actual knowledge of pre-historic humans to speculate about their sexual behaviours (and as with all other human behavior, I'm sure there is and has been great variance in this).
In any case bonobos would not write Kama Sutra even in 20,000 years. Your timescale and argument is way off.
