A few pre-humans migrated from East or South Africa to Mesopotamia. This was debatably anywhere from 90 – 60 Ka (thousand years ago). Many of the migrants died during the journey. God was moving them to the Garden of Eden that He’d prepared in Mesopotamia, likely somewhere in modern East Turkey or West Iran. I believe only one male came to the Garden of Eden (Gen. 2:8,15) by the Tigris and Euphrates rivers. He may have died and have been made alive by God. In any case, God supernaturally breathed spiritual life into Adam and he became a “living being”—specifically a spiritual being that could commune with God (Gen. 2:7). He was made alive in the similar sense as he died the day he sinned. He was called Adam. (It is also likely, though not necessary to this theory, that Adam was the first ‘animal’ to be able to speak, think highly abstractly, daydream, understand music, and etc.)
From Adam God formed a comparable woman with a spirit whom Adam named Eve (Gen. 2:18-22; 3:20). Adam and Eve probably ate of the Tree of Life, which caused their bodies to be continually renewed and regenerated. This effect eventually wore off after many generations. Adam and Eve ate of the Tree of Knowledge of Good and Evil and were driven out of the Garden of Eden to the East (Gen. 3:22-24) by the Caspian Sea or by the Persian Gulf. Myths in several cultures talk about people who used to live hundreds of years (e.g. Sumerians), which further confirms the Bible’s account.
Adam and Eve understood that the other pre-humans that continued to live were still animals and not to be intermarried with. However, sometime during this pre-Flood world, fallen angels likely possessed the spiritless pre-humans and/or Neanderthals and intermarried with many of Adam and Eve’s descendents (Gen. 6:1-2). Mighty men were produced from these hybrids (Gen. 6:4). These mighty men were likely ones who started legends of half-god and half-human beings (demigods).
(From the evidence, it looks like there were pre-humans still existing in Africa—and perhaps elsewhere—that had high intelligence for animals. These pre-humans could likely think semi-abstractly, such that they could draw designs that appear semi-symbolic. It is my guess that these animals would have been smarter than dogs or elephants or dolphins, but still unable to speak, understand music, or truly think abstractly like humans.)
Humans multiplied within the Mesopotamian area. Likely, they didn’t spread out. Violence became widespread and horrible (Gen. 6:5-6, 11-12). It’s likely that the “mighty men” wanted to kill off regular humans. God found a man who was blameless and undefiled in his generations—that is, who wasn’t contaminated by pre-humans and the fallen angels (Gen. 6:9). Noah was chosen to survive a Great Flood. However, at least one of Noah’s daughters-in-law was contaminated apparently directly by Neanderthals or indirectly via pre-humans who’d interbred with Neanderthals; it seems likely that this was Japheth’s wife.
The Flood probably occurred because of the Caspian Sea and/or the Black Sea and/or Persian Gulf overflowing as ice melted and a super-hurricane came and dumped water over the Mesopotamia area. This could have been anywhere from 60 – 50 Ka. Because humans seemed to have spread all over the earth c. 55 – 50 Ka, which would correspond with the Tower of Babel incident, I suspect an early date for the Flood of c. 58 Ka. I suspect that the flooding was massive and covered much of Mesopotamia and some of the surrounding areas, even going into some of Asia.
Every living human died (1 Peter 3:20). That does not mean that pre-humans (other so-called Homo sapiens) didn’t survive in other places. To a secular world, it is likely that the Great Flood might look like nothing more than a typical, large flood. Secularists won’t distinguish between pre-humans and humans—between spiritless beings and spiritual beings. These pre-humans could have interbred with humans later, or they could have remained separate. Minor interbreeding may have resulted in human spirits being passed to them after the Flood.
After the Flood, Noah and his sons left the Ark and repopulated the Mesopotamia area, likely. There could have been some dispersal of the people before the Tower of Babel, but a large majority of them remained there (Gen. 8:4; 10:10; 11:1-2; cf. Josh. 7:21; Is. 11:11; Dan. 1:2; Zech. 5:11). They all had one language and built the Tower of Babel, probably in modern day Iraq. God came down and disrupted their building and confused their language and scattered the people (Gen. 11:6-9). My suggested time for this scattering is c. 55 Ka. Then, all the people spread across the globe over a short period of time. Ice bridges allowed them to cross over into the Americas.
It appears to me that some of Ham’s descendents moved into Africa, and thus Ham and his wife were uncontaminated by the Neanderthals, since African people have no Neanderthal DNA. Also, some pre-humans remained in Africa and Ham’s descendents interbred with them. Ham’s descendents kept migrating all the way to the southern-most parts of Africa. This explains why the Southern Africans appear to genetically represent the earliest humans the best.
It is possible that humans again intermarried with some of the pre-humans possessed by fallen angels, since Genesis indicates that “might men” were in the land after the Flood as well as before (Gen. 6:4).
Eventually, the pre-humans died out, or became humans through intermarriage and obtained human spirits through Adam and Eve’s descendents.
Abraham dwelt in Ur (dated at c. 3000 BC), which was in the Mesopotamia area (Gen. 11:28). This was probably a part of the Sumerian culture.
Finally, in the fullness of time, God sent forth His Son. It is possible that God was waiting until the pre-human kind became extinct. When the Gentile Age began during Jesus’ ministry or at His death, it was important that all Homo sapiens have spirits and be savable people.