Wikipedia puts it this way: "The last glacial period, popularly known as the Ice Age, was the most recent glacial period within the current ice age occurring during the last years of the Pleistocene, from approximately 110,000 to 12,000 years ago. Scientists consider this "ice age" to be merely the latest glaciation event in a much larger ice age, one that dates back over two million years and has seen multiple glaciations."
So, it sounds like the last few million years have been an “Ice Age” with periodic episodes of “warm” weather.
When I referred to “human development,” I was thinking more along the lines of “upright apes” from 3 million years ago to Homo Sapiens about 200,000 years ago.
It seems like any prolonged period of severe cold had the potential to wipe out our poorly insulated ancestors, or the potential to deny them the considerable nourishment they need each day.