It's been known for a while that H. Sapiens weren't the sole human species during the beginning of it's history. H. Neanderthalensis was around with us as well, and it has been theorize that we may have interbreed with their population. The Denisova hominin were around in northern Europe and in the Flores Island in Indonesia, the last vestige of the first wave of human migration lingered as H. Floresiensis. Or so we thought, anyway. There may be new evidence that another human species may have survived in China as the a contemporary of H. Sapiens. Skeletal remains found by Chinese minors, including jaw bones, have been concluded to be different from that as anatomical modern humans, but only dates back to about 14,500 years ago.
I think it's an intriguing thought. If Neanderthal studies have taught us anything is that these four non-modern humans were still just as capable of art and sophistication as modern humans. I will still hold reservations, of course. It's entirely possible for the differences in bone structure be caused by disease or other affliction. Still, it's a great thought.