I believe the oldest Mongoloid skeleton was found around the Lake Baikal area. Oppehheimer's DNA/teeth studies indicated that the North Asian descended from the South Asians and after some isolation in the north, developed the exaggerated Mongoloid features as, flat face, sindonot teeth, lighter skin, etc.
There is one skeleton found around the Lake Bakail area that is 22,000 years old (this is the disputed Mongoloid skeleton), that provokes such arguments that these guys who study such things have stopped talking about it.
Personally, I believe the Mongoloid and Caucasian 'races' were distinguished during the Last Glacial Maximum(LGM), 22-18k years ago from a common source, probably from the Jomon/Ainu types that had already been distinguished from the 'out-of-Africa' types.
The Melanisians (Negritos) were probably part of the original 'out-of-Africa' stock that mingled intermittently with some of the other groups but some remained in isolation ( and not mixing) on the misc islands in the region.
When the Ice Age ended, many millions of people had to move...and, they went in all directions. It wasn't until the final melt/surge 7-8,000 years ago that opened up the Strait Of Mallacca(sp) and allowed these immigrants to sail to India, Persian Gulf, Egypt and etc (Some to the Americas) establishing the ancient civilizations there. Some were probably 'the wise men from the east.'
They brought their myths, garden of Eden, and flood stories with them...maybe even Atlantis stories.