Gen. 1:11 Then God said, “Let the earth produce vegetation: seed-bearing plants and fruit trees on the earth bearing fruit with seed in it according to their kinds.” And it was so.
21 So God created the large sea-creatures and every living creature that moves and swarms in the water, according to their kinds. He also created every winged creature according to its kind.
24 Then God said, “Let the earth produce living creatures according to their kinds: livestock, creatures that crawl, and the wildlife of the earth according to their kinds.” And it was so. 25 So God made the wildlife of the earth according to their kinds, the livestock according to their kinds, and all the creatures that crawl on the ground according to their kinds. And God saw that it was good.
Lev. 18:23 You are not to have sexual intercourse with any animal, defiling yourself with it; a woman is not to present herself to an animal to mate with it; it is a perversion.
Deut. 27:21 ‘The one who has sexual intercourse with any animal is cursed.’ And all the people will say, ‘Amen!’
These verses in regards to bestiality cast doubt on the thesis that humans mated with non-human creatures. The Pentateuch should be understood as a unit providing these kinds of answers in regard to the nature of humanity. It builds up a theology of natural and unnatural relations between humans and other creatures. The idea is that human relations with animals are unnatural because they are not of the same kind. We know things are of the same kind because they are able to reproduce(ignoring genetic drift). Humans were able to reproduce with neanderthals. So, the question arises whether they are of the same kind? If not, then they shouldn’t be able to reproduce. If yes, then they are indistinguishable from being human. So, it then follows that they are human and must derive from Adam given other data. These are just my thoughts on the proposal provided by Dr. Josh Swamidass.