Since the sea level was 300 to 400 feet lower at the end of the last ice age, it seems likely that there are drowned areas around Indonesia that could have given rise to peoples in south India and China, as well as Flores Island. However, I am inclined to think that drowned areas
in the Atlantic, the Indian Ocean and the Mediterranian would be a more likely source of people in the Middle East, the Indus Valley, and the Nile Valley. Lets not forget the possible influence of a great commet crash in North America on relatively advanced peoples.
the Atlantic ocean and Mediterranean seem far fetched considering that the centers of civ were to the east of that. Perhaps the indian ocean