19. Migration waves and genetic diversity

 

The first OoA-migration was around 2 millions of years ago, by H. ergaster groups. Researchers name this OoA-I, and the later one from around 100,000 years ago by the AMH groups is called OoA-II. Within the latter, we see two migration waves: OoA-IIa (between 115,000-74,000 years ago) and OoA-IIb (65,000 years ago, after the Toba bottleneck).

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The AMHs in East Africa developed from a more long and slender, ‘nilotic’[1] Middle-Stone-Age population type some 200,000 years ago. They first dispersed over the African continent,[2] replacing the Early Human populations, who disappeared. 130.000 years ago, a small group left the continent and began dispersing all over the world.

Map of early human migrations according to mitochondrial population genetics. Each character represents a different haplo group. All Out-of-Africa groups descend from the African L3M group.

OoA-IIa took place in a warm period when the Sahara barrier was green. So perhaps the first AMHs left Africa along the Nile. As mentioned above, AMH hand axes are found on the Arabian Peninsula dated 125.000 years ago. Paleos have found fossil AMH remains dated 120,000 years old in the Mount Carmel caves Skhul and Qafzeh (Israël). Their stone assemblages did not differ from those made by the Neanderthals who had survived the severe cold period after the Toba catastrophe in the same caves, which during that period were abandoned by the AMHs. The paleos see the latter as ‘archaic AMHs’, because they do not yet show the more modern life style of the Blombos populations in the Southern tip of Africa.

We can follow the migrations by looking at archaeological remains. We can also reconstruct them by looking at the dispersal of different types of musical traditions

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humans, because in the rest of the world the genetic diversity is much smaller. Tishkoff[4] also suggests that the group which migrated out of Africa came from northern East Africa. "The diversity of groups in Ethiopia and Somalia is intermediate between that of the rest of Africa and the rest of the world," according to Tishkoff: "perhaps this group was isolated from the rest of the African continent before they migrated into the Middle East and Europe." As said, this first OoA-group doesn’t show the life style of the southern AMHs of Blombos cave and other sites. So this archaic group may have been driven northwards along the Nile by the population pressure of more modern AMHs from the south. Because their first appearance outside Africa is on the Arabic Peninsula, near the Strait of Hormuz (Jeben Faya, 128,000 years ago) and they appear in the Levant 8000 years later, it is also possible that they left Africa by crossing the Strait of Bab en Mandab. Or should we suppose two emigration groups of archaic AMHs? Because their stone technology is a little different.

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Most of the ‘archaic AMHs’ (OoA-IIa) moved ‘beachcombing’ to the East. In this relatively warm period, lush vegetation on the Arabic Peninsula made it habitable for grazing animals and their human predators. Recently, African-looking hand axes have been found in Jebel Faya (UAE)[5] . From there, migration to India may have taken place, where we find them

Semang woman, descendant of OoAIIa-people

“spearing dinner and filleting meat” 76,000 years ago in Jwalapuram.[6] At the moment of the Toba catastrophe, most of them had already passed that area, beachcombing farther eastward. Their descendants populated Sundaland and eventually reached the Sahul continent (New Guinea, Australia, Tasmania). Today we still find descendants of these early AMHs in the jungle of Malaysia: the Semang (see photo). The Malaysians name them Orang Asli, and in the Philippines they are named Negritos.

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In their homeland Africa, the AMHs recovered soon after the Toba disaster. Since that time, they developed the modern life style we already mentioned: indicated by fish spears and other tools from bone, ivory and antler, shell beads, engravings on ochre lumps. And perhaps they used spoken language. About 65,000 years ago, their coastal population became large enough to start the OoA-IIb migration wave. This time, they crossed the red Sea at the Strait of Bab el Mandab. Presumably in several waves (see the second map below).

The OoAIIb-migration (post-‘Toba’)

By 45,000 years ago, or possibly earlier, they had settled in Indonesia, New Guinea and Australia.

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Today’s Australian Aboriginals are descended from the first humans to travel far from their African origins. (From: “Aboriginal genome analysis”, Nature. 477, 28 Sept. ’11)

The modern humans entered Europe, inhabited until then by Neanderthals only, around 40,000 years ago. The Neanderthals, who were Early Humans, now were confronted with a totally different kind of humans: noisy, numerous, armed with farther reaching spears and living from fish. People who didn’t react on your gestured communication. So as a Neanderthal, you could better avoid confrontations and retreat into an area without fish. By 35,000 years ago, the AMHs had populated most of the Old World and forced the Neanderthals into mountain strongholds in Croatia, the Iberian Peninsula, the Crimea and elsewhere. The Neanderthal groups became isolated from each other, suffered ever more from inbreeding and would become extinct 25,000 years ago.

Finally, around 15,000 years ago, humans crossed from Asia to North America and from there to South America. The white regions on the map is territory that was never been tread by humans before.


[1] Nilotes are often described as gracile in build, being slimmer and of greater stature than the average human, and having long limbs with very long distal segments (forearms, calves). This characteristic is thought to be a climatic adaptation to allow their bodies to shed heat more efficiently.

[2] "We found an enormous amount of diversity within and between the African populations, and we found much less diversity in non-African populations," Tishkoff told attendees today (Jan. 22) at the annual meeting of the American Association for the Advancement of Science in Anaheim. "Only a small subset of the diversity in Africa is found in Europe and the Middle East, and an even narrower set is found in American Indians." (Science Daily, Jan 25, 1999)

[3] Journal of World Prehistory March 2003 “Language, Symbolism and Music – An Alternative Multidisciplinary Perspective” from Francesco d’Errico et al.

[4] Penn State University

[5] by Hans Uerpmann of the University of Tübingen and his team, in 2010

[6] according to Petraglia and his colleagues

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