Two cultural centers merge
The modern mind had emerged many times in many places in the course of the last two hundred thousand years, only to disappear as food became scarce and populations scattered and broke up into microsocieties that were unable to maintain the funds of knowledge, skills, linguistic forms and vocabulary that their ancestors had accumulated in more settled environments, but between 120,00 and 70,000 years ago rainfall increased throughout Africa, and this enabled a cultural nexus to form that expanded across half of Africa and then moved into the Middle East.
Two cultural centers in Africa -- in southern Africa and eastern Africa respectively -- combined their cultural elements and then began to expand from east to west across Africa. From there, this new, aggressive cultural center pushed north into the central African jungles. There, bows and arrows, which had been invented in southern Africa, were found to be useful inn bringing down relatively slow-moving animals that hid in the trees. The new killing system was also useful for killing fish.
After crossing the jungles into northern Africa, the population waves again moved across Africa, this time from west to east, and then clear out of Africa.
First Anatolians and first Iranians
It has often been assumed that the Out-Of-Africa movement began about 50,000 years ago, but the first fully successful out-of-Africa movement occurred more than 72,000 years ago, just before the explosion of the Toba Super-volcano.
The early pioneers moved north into the Levant and then moved east and further north, into mountainous regions that are now in Syria, Iraq and Turkey. Some of them moved still further east, to the Persian Plateau.
Those who moved into the mountains found the hunting good there, because the rugged terrain provided many opportunities for trapping sheep and goats. Many descendants of these sheep- and goat-hunters are still there today, even though they were reduced to cooking and eating grass seeds with the onset of the Younger Dryas, 12,900 years ago -- about 55,000 years after they had arrived in the region.
Those who continued on to the Persian Plateau found the hunting good there, also. They interbred with the indigenous Homo neanderthalensis; which caused trouble for both species, because Homo neanderthalensis carried an RhDd antigen on the surface of their red blood cells in the place of the Rh antigen. When a fetus carried one type of antigen and its mother carried the other type, the mother's body manufactured antibodies against her own fetus, which flowed into the unborn child through the umbilical cord.
The populations of both species suffered sharp declines in their populations, but as more and more Homo sapiens arrived on the Persian Plateau that species recovered. Homo neanderthal, who lived in small, isolated groups and could not tolerate a high population density, became extinct on the Persian Plateau.
The same scenario played out later, when Homo sapiens later invaded Europe in large numbers. Moreover, something similar might have occurred when Homo sapiens invaded Africa and interbred with Homo heidelbergensis.
The Toba Super-volcano
About 72,000 years ago the Toba Super-volcano on the Island of Sumatra (in present-day Indonesia) exploded, and South Asia was covered by a layer of volcanic ash five centimeters thick.
Skies darkened, and a volcanic winter intensified the glacial maximum that followed. Much of Africa became very dry, and a shortage of carbon dioxide in the air caused all kinds of green plants to grow very poorly. Herbivore populations declined drastically, and most of Africa was denuded of its human population.
However. the population along the southern rim of Africa was not greatly affected, and as a result the Khoisan peoples of southern Africa, who are descended from those who had lived along the southern rim of Africa at the time, now have the greatest genetic diversity to be found among African populations.
The die-off caused by the explosion of Toba left relatively small pockets of human survivors scattered about in Africa, where they survived in small refugia, and founder populations emerged from these refugia to repopulate Africa. The descendants of these founder populations had less genetic diversity than the Khoisan peoples.
Those who had moved north into The Middle East were relatively unscathed by the event, and indeed people who had moved there became acclimated to cooler temperatures, so that after the glacial maximum had passed they were able to move further north into Eurasia where they displaced the indigenous Homo neanderthalensis.
Success in Eurasia
About 45,000 years ago modern humans in the Middle East met with some success when they moved further north, particularly those who then moved to the east across central Asia during a warm period and found that an unusually warm climate in that region had created a string of lakes by which they could slip between deserts to the south and Siberian mountains to the north. In that region they came into contact with Homo longi/denisova, and as they moved across what is now China and into southeast Asia they came into contact with more of these archaic humans. Cross-breeding occurred between the two species, and consequently DNA from Homo longi/denisova can be detected in the genomes of many modern people, particularly in Oceania, offshore from Southeast Asia, where some Homo longi/denisova might have been trapped by rising sea levels.
Modern people also met with some success in Europe, in spite of the difficulty of interbreeding with Homo neanderthalensis, who carried the RhD antigen on their red blood cells. Archaeologist have found evidence that one subgroup of Homo sapiens successfully occupied territory further north than that occupied by Homo neanderthalensis, after passing through Homo neanderthalensis territory about 46,000 years ago and picking up DNA from them. These early Homo sapiens occupied a string of far-north camps across Europe, from modern-day Poland to present-day England.
As they passed through Homo neanderthalensis territory they certainly must have noticed that interbreeding with the indigenous population often led to unfortunate results, and this probably induced them to continue moving north until the climate was too cold for Homo neanderthalensis. Homo Sapiens survived there because they had to, and maybe because their garments were better made.
As Homo sapiens moved into Eurasia in large numbers and interbred with Homo neanderthalensis and Homo longi/denisova they picked up immune-system alleles from them that protected them against novel diseases encountered in Eurasia. These spread rapidly through the Homo sapiens population, so that modern Homo sapiens living in Eurasia now carry these immune-system alleles in their own genomes.
Homo neanderthalensis were driven into extinction by 38,000 years ago, and Homo longi/denisova also became extinct.
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