I wonder what political ramifications this would have. Say these monkeys were intelligent enough to have conversations with and they had thoughts and opinions on the world, but they weren't quite as smart as humans – they couldn't do advanced maths and were intellectually closer to young children – would we deny them the right to vote? Would we deny them employment rights? Etc...

If we did on what grounds would we do so? Lower average intelligence? How exactly could we do that while granting similar rights to humans with equivalently low IQs?

It's hard to imagine that this wouldn't destroy modern liberal societies. We would either grant them equal rights at a huge societal cost, or start denying rights based on intelligence which would come at a huge ethical cost.

I think about this a lot in regards to extinct human species. I often wonder what would happen if we found Neanderthals hiding out on an island somewhere. What rights would we give them? Would we allow them to bred with humans? It seems every answer is wrong.