[ummwhat]

There's two facets of sexual behaviour that are unique to humans. The first is we're the only species that sometimes gets aroused on violence or gets violent on arousal. This is an accident of neurology, both feelings a processed close by. The second is we're the only species that cares if anyone's watching. This observation seems to hold across cultures and time periods.

So the answer is, it was always taboo for kids or anyone else to watch. People may not have always been able to hide it effectively, but they were always at least trying.

[tsimionescu]

> The first is we're the only species that sometimes gets aroused on violence or gets violent on arousal.

Not sure why you think this. Plenty of other animals become violent during marrying seasons, it's often an explicit part of their sexual behavior, at least for males. For example, most horned mammals (deer, buffalos) have violent conquests in the mating season.

[ummwhat]

I learned it from the Stanford Neuroscience lectures available on YouTube. The ones with Dr. Spolansky. I'm not sure how to discern the subtle difference between "a brain liable to conflate sex and violence" with "violent behaviors tangentially related to sex" either. I'm just trusting the scientist telling me the difference is there and they've studied it.