Look, I just wanted to start an interesting conversation and it worked. I don't mind the downvotes because every reply and vote, up or down, means people are talking.

Humans have a pretty spotty history with how they treat each other, it's not a huge stretch to imagine some weird historical moment where consent wasn't a concept or wasn't recognized. The word rape was pretty strong for me to use, but just a few years ago we used to call it date rape instead of just rape.

There's likely no way for us to determine.

It's difficult to determine if someone consented last night, never mind tens of thousands of years before the earliest written histories. We have precious little evidence of what societies were like during that time period.

If only based on typical human behaviour: Probably both. There's always someone that's into something a bit different, so if Sapiens and Neaderthals intermixed sufficiently, there'll always be some couple that gets it on. Hell, there's people that fuck dogs (and dogs that try to fuck people). If dogs had been capable of consenting, I'm absolutely positive that some consenting human/dog couple would exist. I would say that consenting inter-species couples would have been inevitable given enough mixing of the groups.

Then there's also the long history of sexual violence in conflicts. Sapiens and Neanderthals were competing for resources, so there's bound to have been tribal conflict at some point. Just based on how humans behave in that kind of situation, it's pretty much guaranteed that people were raped during those conflicts.