from SAPIENS. … In a study published today in Nature, researchers report that dramatic climate fluctuations created favorable environmental conditions that triggered periodic waves of human migration out of Africa every 20,000 years or so, beginning just over 100,000 years ago.
Why did humans migrate from Africa to the Middle East?
Most likely, a change in climate helped to push them out. Experts suggest that droughts in Africa led to starvation, and humans were driven to near extinction before they ever had a chance to explore the world. A climate shift and greening in the Middle East probably helped to draw the first humans out of Africa.