If one applied the same laws of nature to humans as are applied to wild life, one could surmise that a hard life in a demanding climate removed the weak and the stupid from the human gene pool before they could reproduce. This, of course, strengthened the human population in the northern areas, but just the opposite happened in the southern areas where there was little or no "pressure" on the human population.
Deserts are also demanding environments. I would say it made the Arabs tougher even though today they mostly live in cities.