Here’s an interesting article from “Nature” magazine (August 2018) about the analysis of findings from a Siberian cave (Denisova Cave). What jumped out at me appears on the geneology chart which notes a mystery and unknown hominin species > 1 million years ago from which sprang the hybrids.
62:0.1 ABOUT one million years ago the immediate ancestors of mankind made their appearance by three successive and sudden mutations stemming from early stock of the lemur type of placental mammal. The dominant factors of these early lemurs were derived from the western or later American group of the evolving life plasm. But before establishing the direct line of human ancestry, this strain was reinforced by contributions from the central life implantation evolved in Africa. The eastern life group contributed little or nothing to the actual production of the human species.
64:1.1 Primitivemanmade his evolutionary appearance on earth a little less than one million years ago, and he had a vigorous experience. He instinctively sought to escape the danger of mingling with the inferior simian tribes. But he could not migrate eastward because of the arid Tibetan land elevations, 30,000 feet above sea level; neither could he go south nor west because of the expanded Mediterranean Sea, which then extended eastward to the Indian Ocean; and as he went north, he encountered the advancing ice. But even when further migration was blocked by the ice, and though the dispersing tribes became increasingly hostile, the more intelligent groups never entertained the idea of going southward to live among their hairy tree-dwelling cousins of inferior intellect.