June 08, 2017

Out of North Africa

I had previously called Irhoud 1 "The Father of Mankind" and proposed a "two deserts" theory of human evolution whereby our species originated in North Africa, and was pumped out of it to both the Middle East (and especially Arabia, the 2nd desert) and Sub-Saharan Africa during periods of Saharan aridity. This Out-of-North Africa theory (together with the secondary Out-of-Arabia expansion ~70kya) is responsible for the spread of Homo sapiens around the world.

The discovery and re-dating of modern human remains from Irhoud of course adds support to this theory and places North Africa as the most probable cradle of our species, with a comfortable 100kya buffer to the next place where modern humans are detected (the Omo remains of East Africa), and another comfortable 100kya buffer to the next place (Israel and the Skhul/Qafzeh hominins).

The interpretation of these findings in terms of Homo sapiens emerging out of a sort of multi-regional evolution involving all Africa is of course wrong. There is no reason to think of a single species evolving across the huge African continent. The early distribution of sapiens remains are in North Africa, East Africa, and the Near East, and such remains are absent in West/Central/South Africa.

The multi-regionalists lost the game in Eurasia, as it turned out that Eurasians only have ~2% archaic admixture, and they are inventing Multiregionalism-in-Africa.

Whatever finds we do have from Sub-Saharan Africa, some of them quite late (such as the Iwo Eleru remains from Nigeria), others of similar age as Irhoud (such as Florisbad and the recently described H. naledi from South Africa) did not belong to our species. The first modern humans appeared in South Africa with the Later Stone Age (probably associated with the migration of Y-chromosome haplogroup E into Africa), and the Hofmeyr skull (which resembled Eurasians and not the eternally romanticized Khoe-San). Even in East Africa the advent of modernity was not clear-cut (see Omo I vs. II and the more archaic later Herto specimen).

It seems that people were misled into thinking of Sub-Saharan Africa as the origin of our species by the genetic observation of greater genetic diversity of Sub-Saharan Africans. But, this diversity could have come about by admixture between people from North Africa and pre-existing people of Sub-Saharan Africa (both early waves of AMH and non-AMH).

It's not certain that North Africa will be the end of the story. Fashions shifted from the Near East to East Africa, to North Africa, with every new find. But, the fact that we do find the earliest modern humans in these areas, while we find non-AMH elsewhere (e.g. Europe or South Africa) is gradually constraining the solution to the problem of our origins. My bet remains North Africa; time will tell.