There were populations roaming all our continents already DURING the major ice-time, that ended 10.000 years ago.
Since the ice covered the northern hemisphere these various populations/cultures/civilizations had to keep themselves within the southern hemisphere.
Surely they were all tropical, - since the origin of man was due only under tropical/semi-tropical conditions.
Thats why you may find "negritos" in S-America, Africa, Southern Asia and Australia.
During the old and most extensive ice-time, some million years ago, the consequences of the frost was effective down to the 45th paralell.
Due to the pressure of the enormous ice-cap of the northern hemisphere the continents were pushed, to create the enormous mountain-chains of middle-America and middle Eurasia.
North of Mexico the ice were excluding most mammal populations, with the exeptions of the Floridan and Californian penninsulas.
Likewise the big mountain-chains that separate the arctic from tropic Eurasia was formed in a wavy line from the Atlantic to the Pacific. Just have a check on your globe and you may follow the gross line - between the 40-50 latitude - from the Pyrenees to Mandchurian side of the Himalayas...
Since we still have some ice left aorund the poles we can get a nice clue to the picture of the big ice-age - as it looked more than 120.000 years ago. The red color here actually corresponds to the "inhabittable areas" of the gross ice-time:
For some reason there was some people that made a distinct exeption to their natural way of (tropical) living. Somewehere along the Atlantic facade of Europe there was a handfull of people trapped above the 45th parallell, where they (also) became isolate from their tropical relatives. During that time they grew pale, i.e. white - while the various tropical populations still kept our original brown-skin/brown-eyed/black-hair features.
In the Himalayan region a similar trapping of Asian people are known to have happened, which today can be seen in the less pigmented chineese, i.e. the monguls/tibetans. who became "mellow yellow".
Due to continental drift the separation between the humans made the various populations develop specifc customs and traits - according to the respective conditions of the various continents AND their specific climates. Plants and animals was developing into various "blends" accordingly, to become Austrailian, Melanesian, Indo-Chineese, Chineese, Indian, African and American.
When ice-time started to "loosen up" some 120.000 yrs ago a certain movement along the N/S border, started to RE-CONNECT the various populations of Eurasia. Thus we have the meeting of Neanders and Cro-Magnons along the Alps and Caucasian ridges.
When the ice finally disappeared in N-America and Northern Eurasia - some 20.000 years ago - travel and re-union increased. Finally, as the northern ice-cap broke up in the N-Atlantic the enormous ice-sheets would drif into the lower altitudes, reach the ocean and melt away.
10.000 years ago the melting-process was done and the pale-faces from the east Atlantic were able to reach the Caucasus and the Med, to reconnect with the tropical populations. At the same time this arctical people - used to cold temperatures, harsh conditions of nature and long, dark winters - were able to explore northern Eurasia. Thus they started to populate the arid landscapes of Northern Europe and Russia and start deveoping local niches of vegetaion and food-supply.
Seemingly, the harsh conditions of ice-time had made a specific surplus of big and strong individuals among the few survivors of the desolate north. When they came to meet their long-lost cousines of the tropical areas they turned out to be remarkably higher.
During the comming millenia of re-connection the caucasians were able to reach all the tropical cultures. Bringing about the "productive elements" needed to survive ice-time in the arctic/sub-arctic they instigated the techique of domestication, which ultimately brought neolitization to both America, Africa and Asia. Along with the extraordinary use of fire that allowed "metamorphosis" - i.e. melting stone to formable metals. The consequent formation of metal-tools made stone-cutting possible, which finally grew into megalithic constructions, marble columns and "cut-size" building-b ricks.
Along the way the tropical populations all got mixed with these sun-tanned caucasians, to re-create a genetic, cultural and linguistical community of all human beings - without distorting the physical and cultural characteristics of the various regioanal populations. Consequently there is - today - a strong, reinforced tie between the united humanity as it originally was - before the split of ice-time - and todays modern humans.
Whatever the ways and means have been we're finally back to state of affairs where ALL people of the globe can share the same physical and mental abilities - as to communicating, relating AND
- even - mating, without peculiar difficulties.
During the last millenia we've had a lot of bad effects from the turmoils of these meetings. But, at the same time - during this time and processes - we have gained a state were enormous amounts of people are able to travel and communicate world-wide, in a language that today are spoken and understood in all corners of the world.
Finally we can appreciate the same origins again too, as the evolution of our biology, speech and history are understood. That means that we do not have different physiognomy anymore, like they did in the paleolithic time. Neither do we have different origins and "kinds" anymore, since we now can understand that we all actually come from a common pair of ancestors - just as the collective memories of this one-and-the-sanme origin are describd in all major myths of the ancient world...