Humans first started out of Africa and spread out over middle East, Europe and Afghanistan and subsequenty the south East and far East.
We have all started our evolutionary journey from Africa I guess after we climbed down from our arboreal perches and gave up our fruit eating habits (for grain which enabled us to eat less meals and utilize the time for more creative pursuits).
Gradually over cultivation has done away with our forests and created large tracts of arid land (there are natural factors to desertification as well other than humans but then we are just focusing on humans here).
Added to this humans have augmented the process of desertification through concretization and furthered it through inter racial conflicts.
At the moment the health of Earth is at stake and human health is obviously related to it.
A possibly related article:
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1123576
My apologies if this post was not related to vital local issues but was a vague rambling on issues in general about the Earth and its health.
