The Sons of Noah: Known and Unknown
by Jon H Benson
(Whitehall, PA USA)
Looking at the lists of offspring in the book of Genesis, (and remembering that the book relates not just the beginning from Adam and Eve, but also the re-genesis of mankind from Noah and his wife after the flood) it seems to be that if the sons (offspring) are mentioned, no matter by which child, they will somehow show up again at a later date, usually as some distantly related relative or tribe.
Hence we know that Ham's descendants became the Canaanites, and the bane of Israel, and some of Japheth's kin became the Assyrians and Chaldeans and Medes, etc, and of course, Shem's line produced Abraham and God's chosen people. This seems to be the case wherever descendants are mentioned, from Noah, to Abraham; Isaac by Sarah, Ishmael by Hagar, and Midian etc, by Keturah, the Moabites and the Ammonites by Lot, the Edomites by Esau. The fact that the heirs are mentioned seems to foreshadow their having some interaction with the Chosen people at a later, if not sooner, date.
So, one might assume that the peoples who moved out to inhabit the rest of the post flood world, that is, the part that would not be directly involved somehow in the line of the Messiah, were not among those listed in Genesis. One might also assume that Moses, who lived for 350 years AFTER the flood, would have had plenty of time, and inclination, (see Gen. 25:1-6 for an example of the "inclinations" of the patriarchs) to father more children.
And he might have done even as Abraham did, which, in fact, may have been a custom originating with Noah, which was to send the "non-lineage" offspring to far off realms. The Midianites show up again in Moses time, but then disappear from Biblical reckoning. Considering the longevity of Noah and his sons, and the fact that their genes would still carry much of the anti-diluvian vitality that the post flood people did not, it would have been in the interest of humanity to spread those qualities as far as possible in the new world. Some of Japheth's or Shem's descendants might have also done as Abraham did, and sent their children back to marry cousins, offspring of Noah, whom, by definition, would be purer than the surrounding tribes.
In any case, it doesn't seem necessary to have to populate the entire earth over again from just the three sons mentioned in the Bible.