Whether early Homo sapiens interbred with ghost species or inherited ghost DNA through Neanderthals and Densiovans who interbred with them, their identity still eludes us. This ghost species responsible for that mystery 1% of DNA probably lived around a million years ago. When and where the introgression events that introduced ghost DNA happened also cannot yet be inferred. However, the researchers predict that new reference genomes may eventually elucidate this, and could also tell us something about how the ghost genes contributed to human evolution. “[Ghost genes’] roles in immunity and metabolism have yet to be fully characterized,” they said.