The early landscape shifted between woodland to grassland half a dozen times over 200,000 years, meaning man had to adapt to survive.
Experts from Penn State university say that this may have set the tone for the rapid evolution which then took place.
Writing in the Proceedings of the National Academy of Sciences, Clayton Magill said: "The landscape early humans were inhabiting transitioned rapidly back and forth between a closed woodland and an open grassland about five to six times during a period of 200,000 years.
"These changes happened very abruptly, with each transition occurring over hundreds to just a few thousand years."
The findings appear to contradict previous theories which suggest evolutionary changes were gradual, and in response to either long and steady climate change or one drastic change.
Professor Katherine Freeman said: "There is a view this time in Africa was the 'Great Drying,' when the environment slowly dried out over 3 million years.
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