Most anthropologists believe that modern man evolved in East Africa, about 125,000 years ago; this coincides with the last, warm interglacial period of the Pleistocene and precedes the Wisconsin Glaciation. Likely confined to Africa for 50,000 years or more, humans began to spread beyond their home Continent as the climate cooled, precipitation increased and the vast Sahara Desert began to retreat. The gradual formation of the Wisconsin Ice Sheets, beginning about 75,000 years ago, tied up an increasing supply of Earth's water and sea levels started to fall; at the peak of this glacial period, about 25,000 years ago, sea level was 400 feet lower than it is today.
As sea level fell, the exposed Continental margins spread outward, archipelagos became long peninsulas and offshore islands were attached to the mainland; eventually, the broad Bering land bridge connected Asia with North America. DNA studies suggest that man first spread along the southern edge of Asia, reaching Southeast Asia by 70,000 years ago. Since most of the large Indonesian islands were then part of a broad peninsula, he was able to rapidly colonize much of that region; within another 10,000 years, he reached Australia, crossing an open channel in primitive, raft-like boats.
A land bridge connected Japan to the mainland of east Asia and man colonized that future island country by 50,000 years ago; about the same time, the Arabian Deserts had retreated in the cool, wet, periglacial climate and humans were moving northward into western Asia and southern Europe. By 25,000 years ago, humans spread across the Bering land bridge and would colonize both of the American Continents within another 10,000 years; there is increasing evidence that man also arrived in the Americas from the east, hunting his way along the ice pack of the North Atlantic.
It is clear that the Wisconsin Ice Sheets played a major role in man's dispersal across the globe. Had this last Pleistocene glaciation not occurred, human colonization of Australia and the America's would have been significantly delayed. What impact that would have had on the development of human culture in Europe, Asia and Africa is open to speculation.
