Human beings, in this plane of existence, have always been the humans on this world. When they devolved from higher states and gross living matter (mold, fungi, r. plants, complex plants) evolved to generate a stable biological ecosystem into the continued evolution phase (where we are now), what human beings were was not biologically similar to what we are now, in the evolved phase. The world was evolving, higher beings were becoming what we are now. I am not claiming that there was a separate human species in the past, but that the human species was quite differently physiologically during the evolving phase. Make sense?
Thank you for at least listening to my explanation.
Sometimes no Buddhas arise in the world. Sometimes they do. When it happens, it is for the welfare and happiness of men, out of compassion for all creatures. For a long, long time he has been working to become a Buddha. He met other Buddhas along the way. And after his long striving he attains his final life, yet not without showing everyone else how to get there.