If you want a serious answer, you're going to have to specify what you mean by "ancient humans". Are you talking about Homo Sapiens, or about earlier versions of humans? Because that will get you different answers, and if you're looking for an answer on the latter you might want to ask anthropologists or biologists. If you're talking about us, it would help to specify what era and region you're thinking of. People living in ancient, civilised China might have had other sleeping habits than European cave dwellers, for example.