This gets into a really complex topic about what is a species. Everyone considers lions and tigers separate species yet put them together they will interbreed creating a liger [0]. Ligers are even fertile.

As for what it means if some of us have Neanderthal DNA and some don’t is some of us are a hybrid species [1].

0. https://en.wikipedia.org/wiki/Liger

1. https://en.wikipedia.org/wiki/Hybrid_(biology)