Something we tend to do is not look back far enough. There were three ice ages and four interglacials in the last 350,000 yrs. It happens in a regular cycle approximately every 125k, so since the earliest known Homo erectus find dated to 1.8 million years ago there have been 14 glacial/interglacial periods where migration could have been necessary for survival of hominids.
Each of these could have been associated with migrations north/south again as these cycles came about, and each would have resulted in it’s own post migration evolution depending on location and environment. There were ice ages before the last ice age and we limit our scope of perspective to only the last ice age and it is a mistake, we need to look at the longer time line and consider there were actually 14 of these cycles.
Very good points - and the dates may go back further than 1.8 million years.
A lot of people in the Anthropology business seem to believe that Homo Erectus evolved outside the African continent.
I get the impression that theory might be very dangerous for job security in the academic world, and it's rare that I see detailed commentary on that idea.