BOTTLENECK

A Garden of Eden

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Our direct ancestors of 1.2 million years ago consisted of about 26,000 breeding pairs, but this was reduced to only about 1,200 by the time glaciation had reached its peak, about 930,000 years ago.  Glaciation at the poles of the Earth and global cooling. unfortunately, were accompanied by intense dryness in much of Africa.  This combination made it very difficult for hominins to survive, because the northern polar cap advanced to just north of the Carpathian Mountains.  Moreover, extraction of carbon dioxide from the air by the cold conditions and the massive buildup of ice at the polar caps brought yet another worldwide problem for herbivores and humans alike:  plants grew poorly because they needed carbon dioxide in order to grow.  Hunting was very poor everywhere because of the slow growth and poor quality of every kind of plant.

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Between 1.2 million and 900,000 years ago, as the polar ice cap advanced toward the Carpathian mountains, our ancestors must have followed migrating animals south as they followed rivers that even then flowed south through Mesopotamia to a swampy delta near where the Persian Gulf is today.  There, they found a refugium for herbivores and humans alike, because grasses and other plants in and around the swamps were well-watered even during the driest part of the year.

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A fly in the ointment

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The swamps were not an ideal place for hominins, for several reasons.  First of all. the hominins found that drinking the swamp water undermined their health.  Children who drank the swamp water often did not reach maturity and left no descendants.  This caused the total population of those who had reached the swamps to rapidly shrink to a little more than a thousand breeding pairs.​

Roots and other vegetative food that people found in the bogs was not enough to increase their birth rate, and the hominins moved too slowly in the bogs and swampy areas to trap and slaughter animals, so the total population of humans in that region stayed small for more than a hundred thousand years.

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This problem forced the hominins to invent percussive signals with which neighboring hunting groups could communicate with each other, even though the hunting groups generally spoke mutually unintelligible languages.  This was necessary because trapping and slaughtering animals required more manpower under those conditions.

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Primitive signals were invented that enabled a hunting group to summon others for help; but then, there was often not enough food to go around.  This prompted the hominins to go after hippopotami.

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Hippopotami

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Hippopotami foraged at night and rested in the water during the day, so the hominins needed to creep up on the animals while they rested in the water and wait for two males to fight over a female.  Then they would rush in and cripple one of the animals.  The result was often a dead hippo floating on the water, which needed to be dragged to dry land and butchered.

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This all took a lot of manpower, but the end result was worth it!  The hominins would butcher the beast and divide up the pieces, and nobody went hungry.  With enough to eat throughout the year, the total population of our ancestors began to grow steadily, and our ancestors at the same time kept learning how to communicate with each other by using percussive signals and how to organize on a large scale even though the individual hunting groups spoke mutually unintelligible languages.

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Homo heidelbergensis

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About 800,000 years ago rainfall increased in Mesopotamia, and some part of the human population that had taken refuge in the Middle Eastern swampland moved north along rivers and then crossed over to a rift valley which separated the Levant from Mesopotamia, and found elephants migrating north and south along a valley that ran north and south through the Levant.  Naturally, these hominins made hand axes out of rocks from a nearby outcropping and started slaughtering the beasts.

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Archaeologists found evidences of a campsite near a pathway that was used by elephants as they migrated.  This archaeological site is known as Gesher Benot Ya'akov, and among the evidences that were found at the site are the remains of a huge carp fish that was roasted there about 780,000 years ago.

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Archaeologists named these hominins Homo heidelbergensis, in honor of a huge jawbone that was found near Heidelberg, Germany, but most of these Homo heidelbergensis stayed in the Levant, where the hunting was good -- until the elephant population dwindled there.

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Between 800,000 years ago, when Homo heidelbergensis first appeared in the Levant, and 400,000 years ago, by which time elephants were extinct in the Levant, the Homo heidelbergensis population continued to drift north and south out of the Levant, following the animals that they hunted.  Gradually, the hominin population of Africa increased, but those who had moved into Eurasia seldom survived the recurrent glaciation there until two new species arose that could deal with the vacillating climate:  Homo neanderthalensis, who eventually occupied all of Europe and as far east as the Ural Mountains, and another hominin species who occupied territories east of there.

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Homo neanderthalensis and Homo longi/denisova

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The earliest remains that have been identified as belonging to Homo neanderthalensis (named after the Neander Valley in Germany) were found in northern Spain, in the Atapuerca Mountains (not far from where fossils of Homo antecessor were found).  They took over Europe after Homo heidelbergensis became extinct.​​​

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The other hominin species that emerged in Eurasia was first identified only by their DNA, which was found in Denisova Cave, in southern Siberia.  Fragments of bone containing their DNA, mixed in with the dirt in the cave, were probably deposited on the cave floor along with the feces of hyenas who had chewed on the bones.

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Identifiable fossils, such as skulls and crania, were later found in China and identified as a new species of hominin which was named Homo longi by archaeologists.  DNA could not be extracted from the fossils, but their distribution suggests that Homo longi was the species whose DNA was found in Denisova Cave.  I will tentatively call this species Homo longi/denisova.

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Their DNA has also been detected in the genomes of modern people whose ancestors lived in Asia or in Island Southeast Asia, and this provides us with clues as to where Homo longi/denisova lived before they became extinct, and people who live in Oceania (islands offshore of Southeast Asia) have especially large amounts of Homo longi/denisova DNA in their genomes.  Nobody knows for sure, however, where the ancestors of modern people in Island Southeast Asia came into contact with Homo longi/denisova.  But the latter might have entered Oceania earlier, when the islands were connected to the mainland.​

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The two Eurasian species or subspecies, Homo neanderthalensis and Homo longi/denisova, obviously interbred when they came into contact with each other.  We know that because fossils of both species contained DNA sequences that they must have exchanged in that way.  In addition, both species interbred with modern humans, on occasion.​

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Parallel evolution?

Lots of African Homo heidelbergensis fossils have been dated to between 700,000 and 400,000 years ago, but as the magic date of 320,000 years ago approaches the fossils become exceedingly rare.  This has allowed some archaeologists to presume that features of the archaic Homo sapiens skull that differentiate the latter species from Homo heidelbergensis -- compressed face, tall cranium and sharp chin -- evolved from the quite different features of African Homo heidelbergensis, and that this evolution occurred right before the archaic Homo sapiens face began to appear in fossils that were found in various parts of Africa.

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Backing up this theory is the fact that human genetic diversity is higher in Africa than anywhere else on Earth.  However, there is evidence that archaic Homo sapiens did survive in the Middle East until late in the Holocene until they were almost entirely wiped out by Sumerian farmers.  We will deal with that later.

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​African Homo heidelbergensis were contemporary with the sudden appearance of archaic Homo sapiens, in various places around Africa -- including Zambia, where a contemporary Homo heidelbergensis fossil was found.  The archaic Homo sapiens populations that popped up about that time had several distinctive features in common, including high, domed foreheads. flat and compressed faces, and sharp chins.

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I think it is time to accept that the sudden appearance of Homo sapiens features in the African fossil record is indicative of an influx of hominins into Africa from someplace else.  I suggest that they came from the Middle East.​​​​​​​​​​​​​​​​​​​​

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Incidentally, descendants of the hominins who hunted Elephants to extinction in the Levant seem to have survived there ​until about 130,000 years ago.  Their fossil remains were found at Nesher Ramla in central Israel, and stone tools that they had produced were found nearby.  Both the fossil remains and the tools were dated to roughly 130,000 years ago.

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Percussive signals

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Those who had left the swamps of southern Mesopotamia to become elephant hunters contributed to our ancestry -- particularly those who later moved to Africa.  But we are mostly descended from those who stayed in the vicinity of the swamps of southern Mesopotamia.  There, they had continued to hone the communication skills and social skills that they needed in that very special environment. Also, for a variety of reasons, they needed to further develop and elaborate on their primitive percussive signals in order to do well in the swamplands.

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Percussive signals enabled our ancestors to organize and cooperate on a larger scale than hominins who had moved elsewhere after the "bottleneck" of about 900,000 years ago.   But even more crucially, use of the signals forced them to develop a special talent for decoding information that is coded sequentially.

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This is because spoken language was almost always combined with gestural language, and our ancestors of the time had up until then never developed the capability of expressing three-dimensional concepts except by combining their spoken language with a gestural language.  But a language based on percussive signals cannot be combined with gestures, because when people communicate by means of percussive signals, they are often at some distance from each other, and often cannot combine the percussive signals (which are coded sequentially) with gestures (which can more easily convey three-dimensional information).

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Spoken language, like percussive signals, is coded sequentially.  Most languages are built out of phonemes, words, phrases and sentences; and strings of phonemes constitute words, strings of words constitute phrases and sentences, and strings of sentences constitute a message.  Since two people who are communicating by speaking to each other are generally in close proximity to each other, and can see each other, they can easily combine their spoken language with a gestural language.  Thus, it had never before been necessary for our ancestors to convey three-dimensional concepts by means of just their spoken language, without the use of gestures.

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A gestural language can easily convey spatial concepts by hand or body movements, while spoken language, without gestures can only be coded sequentially.  Percussive signals, on the other hand, were used mainly for long-distance communication, and it was often impossible to accompany the signals with three-dimensional gestures.

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It was impossible, at first, for our ancestors to convey as much information as they would have liked to convey by the percussive signals.  This is because they had simply never evolved the mental equipment to code three-dimensional concepts in a sequentially coded message.  Indeed, even modern people are unable to do so if they are born deaf, or for some other reason have little or no exposure to a modern language.  But three-dimensional concepts are so important that in the course of hundreds of thousands of years our direct ancestors evolved this important capability -- especially those who stayed in the swamplands of the Middle East until relatively recent times.

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The use of percussive signals, especially those that could convey three-dimensional concepts (like the movements of people and animals) was crucial for coordinating large-scale hunting expeditions.  This was especially true when the hunters did not all speak the same language -- the percussive signals often served as a lingua franca for people who could not understand each other's spoken languages.

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Hand axes in Arabia

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Around 400,000 years ago rainfall increased greatly on the Arabian Peninsula.  Hippopotami from the swamplands began to forage in the wet grasslands that then separated the swamps of southern Mesopotamia from Africa, and some of our ancestors followed the animals until they found themselves in Africa.

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In Africa, our ancestors found that they had been preceded by Homo heidelbergensis, who had entered Africa in large numbers from the Levant.  No doubt the two close species interbred, but our ancestors were so outnumbered that they simply disappeared into the Homo heidelbergensis population without changing it much.  Our ancestors did, however, leave some hand axes on the Arabian Peninsula for archaeologists to find.

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A few thousands of years after this wet period, rainfall declined on the Arabian Peninsula dry conditions again prevailed until wet conditions re3trned about 320,000 years ago.  During this second wet period, hippopotami and other animals again wandered across the Arabian Peninsula, and more of our ancestors followed them into Africa, and they left some of their hand axes along the way, but this time they were met there by only a few Homo heidelbergensis, and our ancestors took over Africa.