I figured I should comment on at least one thing:
Serpent wrote:Thing Two: Europe, the Americas, Asia and Africa were ethnically coherent -- there is a better word that escapes me atm -- until European aggression messed it all up. Toothpaste doesn't go back in the tube and chicken have to roost somewhere.
There is a long debate on what "ethnicity" means such as how often ethnicity is imagined or created (circumstantialist approaches usually following one interpretation of F. Barth's famous chapter) vs. truly inherited (primordialists - I cite Gil-White's 2001 paper in Racial and Ethnic Studies) but virtually all place ethnicity as beng somewhere between race and tribe (both also problematic terms). So...
I find it hard to imagine Europe as being ethnically coherent. Although certainly a bit of a back water in terms of population movements over time, probably the last time it could be called ethnically coherent was when the Neanderthals ruled there before anatomically modern Homo sapiens muddied things up. There might have been quite a while of stability with mostly amHs with some variable amount of Neanderthal dna (and culture?) before the (swarthy?) Indo-Europeans moved in. And then we know historically about those Mediteranean Romans who also brought along soldiers from all over their empire. Lots of Arabic Jewish communities in Europe go back to these times but since became so inter-mixed that it is difficult to think of Jews as being anything but pure European. (And I know of the many debates about the extent to which Judaism is an ethnic group, religion and/or of a socio-political movement with only imagained claims (a la Anderson's Imagined Communities) to being an ethnicity or religion - kind of like "Christians" who don't take into account anything other than some select European "strains".) And through time there were all kinds of barbarians from the east who raped and pillaged their way across Europe fragmenting groups, etc. My own "pure" British (historically although we have een in the New World for 400+ years) immediate family shows some of this with my mother's maiden name being classic Saxon while my father's surname being Anglicized Norman. Read the classic "Ivanhoe" for a great take on that ethnic history.
However, both the Americas before contact and Asia were even more ethnically diverse. Ask some old Japanese bigot wht they think about Koreans and the Ainu and you would get a surprise. That get magnified when you compare the history of the Han Chinese with Mongoleans and the Tibetans. Compare them with the Arabs (and Jews) of SW Asia and the idea of any kind of coherent "Asia" is quicly just a fiction of western views of the world.
Of course the America's are even more ethically diverse with far more diversity in language, religion, economy, political structure, etc. Would you really lump the Plains Indians of Dances with Wolves with the Aztecs and Mayans?
Now Africa is, IMHO, the most diverse although European history still prefers t think of it as an unusual amalgam (for political/exploitive purposes I am surprised you are unaware of). While up to the 19th century political structures literally did range from simple hunter-gatherers to kingdoms, Africa is the only continent that actually has more than one real, genetically-identified race!!! Oh, and by the way, the slave trade in eastern Africa was active across the Indian Ocean for a good 2000 years before the Americas began to be colonized by Europeans which is actually making a bit of a difficulty for looking at changes in skin colour, etc., in southern India, the SE Pacific, etc.