From this brave beginning came the entire population of the world outside Africa. Of course the descendants of these colonists eventually outstripped the population of Africa by a factor of 10, with corresponding gains in wealth and power. Reader explains Africa's handicaps in terms of disease and climate. The liberation of Africa from these enemies began with the period of European exploitation and has continued, somewhat haphazardly, as European drugs are exported to Africa. But it takes more than the potency of African diseases to explain why Africa south of the Sahara lagged so far behind other continents in wealth and power.
Reader has an excellent chapter on early Ethiopia that puts the point well.
By the fifth century A.D. they had not only conquered their African neighbors as far as the Nile, they sailed back to Arabia as colonizers and imposed their will on the states from which their ancestors had migrated. The Axumites traded with the Greco-Roman world, exporting ivory, rhinoceros horn, hippopotamus hide and slaves. Ezana, the Axumite King, was converted to Christianity in 430, and Ethiopia is thus the oldest Christian state in the world. But the decline of the Roman Empire and the rise of Islam in the seventh century progressively isolated Ethiopia from Egypt, Arabia and the Near East. The answer seems to be that, geographically, the Ethiopians were uniquely fortunate.