I brought this up in the Biblical Accuracy forum under the topic of 'Where did the Egyptians come from?'
The best Biblical answer to this question Peter, I believe is found in Gen.10. It would appear that the Egyptians would have descended from Ham. Hams sons were Cush, Mizraim, Phut, and Canaan.
Mizraim(v6,13-14: 1Chr.1:8-11), progenitor of various Egyptian tribes. "Mizraim" means "double". Tribes of the double Egypt(upper and lower Egypt), called the land of Ham came from him (Ps.78:51; 105:23-27; 106:22). The Philistines would also appear to have come through Mizraim as well(v14).
I can't find my previous post on this, and I haven't recalculated the time from the bible, but I beleive that these alternate cultures had on a matter of a couple hundred years to develop ... from originators with first hand knowledge of the power of the one god ... and some of the elders lived into their hundreds still producing offspring.
We have second or maybe third generation believers developing a polytheistic, Pharoah-is-god culture with vastly different world-view to Noah's children in only a couple of hundred years ... not to mention the populational support required for the culture.