From: Bruce Sherrod
>the onset of an ice age would mix the human genome by concentrating
> humans in equatorial warmer regions.  Then, when the ice age ends,
> humans enter a "boom time" economy .

The onset of the glaciers was the boom time.  At the peek of the ice age the
temperate zones contained very large areas of steppe-tundra.  The
Pleistocene Megafauna and the humans who preyed on them would be at their
maximum populations at this time.

When the ice receded was the time of stress.
See:
Cohen, Mark Nathan "The Food Crisis in Prehistory: Overpopulation and the
Origins of Agriculture" in the bibliography at my site.

Ray Audette
Author "NeanderThin"
http://www.neanderthin.com