A DIFFERENT PATH

Eurasian hominins

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Hominin evolution took a different path in Eurasia than it did in Africa.  We know very little about this stage in our evolution, partly because so much has been erased by glaciers, but we will try to resurrect some of the likely signposts along the way:   domestication syndrome, trapping and slaughtering animals, dangerous predators, teaching and learning, language, anatomy, physiology, and onset of the Ice Ages.

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Domestication syndrome

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When the Mediterranean Sea refilled with water about 5.3 million years ago, our own ancestors found themselves north of this inland sea, in Eurasia, where conditions were somewhat different from those in which the Australopithecines and Paranthropines evolved, and one result of the different conditions in Eurasia was an evolutionary shortcut known to scientists as domestication syndrome.

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In Eurasia, the groups who moved fastest across the countryside did best, because they were most successful at finding unbroken bones of very large animals but they tended to become isolated from other groups, and inbred.  Thus, evolution took a much different turn than in Africa:  a scattershot of local characteristics arose in Eurasia, and among these was an evolutionary shortcut known as domestication syndrome.

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Intense competition among mature males over control of receptive females made it more difficult for group members to cooperate in dealing with the new conditions that terrestrial hominins found in Eurasia, and the solution to this problem was for adult hominins to remain immature in some of their behaviors even as their bodies became fully mature:  otherwise mature males neglected to compete over access to receptive females.  Since the groups were isolated from each other, and the groups were highly inbred, it mattered little who was the father of which child, and this evolutionary shortcut turned out to be a viable solution to the problem.

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The suite of characteristics known as domestication syndrome easily appears among wild populations when immature behaviors and other characteristics are not weeded out by evolutionary pressures, and the isolation of the wandering groups and consequent inbreeding allowed immature behaviors to persist.  Moreover, the groups in which the immature behavior persisted were very successful, and eventually came to replace other wandering groups in the total population.

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Domestication syndrome, which appears when wild animals are domesticated, results from delayed maturity of certain cells early in development inside a mother's womb; the tame disposition of domesticated animals is really just immature behavior.

Trapping and slaughtering animals

When, on occasion, the previously semi-aquatic hominins were unable to find unbroken bones from which to extract marrow, they were faced by a crisis, because the shoreline was generally far away, and they were unable t maintain their population size by eating vegetation -- if a small, isolated group tried to survive on vegetation for a long period of time, the group could shrink out of existence -- because the hominins' digestive systems were unable to extract enough energy from such foods to maintain their numbers.  If bone marrow was not available, a group would have to fall back on another skill:  the trapping and slaughtering of terrestrial animals.

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The ancestors of these newly terrestrial hominins had trapped animals in deep water; but in their new terrestrial environment, deep water was not always at hand, and the hominins needed to develop new techniques for trapping and slaughtering animals.  For this, as well as for protection against predators, our wandering ancestors needed extra mature males in their foraging groups.  Yet their foraging groups needed to be small enough to live on the small amount of bone marrow that was sometimes their only subsistence.  An evolutionary process known as self-domestication enabled the patriarch of a group to tolerate the continued presence in the group of other males who had matured.

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Groups where the extra males were allowed to stay in the group after they had matured were better at trapping and slaughtering animals, not only because this provided the group with mor experienced adults, but also because it favored ​cooperative and playful behaviors.

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Selection pressures were very strong for these new behavioral characteristics, which can appear in only a few generations under strong selective pressures, but it has taken humans hundreds of thousands of years to fine tune these characteristics and bring them to full flower.

Dangerous predators

Our terrestrial ancestors, in the course of the next million years, became expert at trapping and slaughtering animals in a variety of environments and using a variety of methods, but they faced other challenges as they wandered about in Eurasia, such as the small and large predators that sometimes picked off their members, one by one.  Even small predators were dangerous to immature members of a group.

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The safety of immature members had previously been almost entirely the concern of their mothers, but as the hominins began to wander far inland, the safety of youngsters had to become a concern of the entire group, because a wandering, isolated group of hominins had no future if their youngsters did not survive.  The only groups who passed on their genes to new generations were those in which all of the group members kept a sharp lookout for predators that could harm the youngsters.

Teaching and learning, and language​

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Whenever a small or large predator was spotted, our terrestrial ancestors passed the word by tactile contact or by hand signal, rather than by vocalization.  This was because vocalization could attract the attention of predators, especially large predators.  Immature individuals needed to learn these signals so that they could also spot potential dangers to themselves or others.

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Young hominins needed to  learn other things, as well, such as how to participate in trapping and slaughtering operations, which also involved hand signals that could be used in order to convey plans, signal intentions, and coordinate activities.  Young hominins learned those signals, as well, and a language of hand signals was passed on from generation to generation.

In the course of time, the cohesive nature of hominins society, their use of weapons, and their genius for communication enabled them to become apex predators.  They were also so formidable in defending themselves that even large predators came to avoid them, and they may have begun, even at this early time, to combine their hand signals with invented vocal signals.

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Apes use body language to signal their intentions, but very few of their vocal or even hand signals are intentional -- their vocal signals are primarily involuntarily, and they do not use complex hand signals.  Obviously, complex hand signals were precursors to vocal signals, and this conclusion is confirmed by the close connections in the brain between intentional communication hand signals and intentional communication by vocal signals.

Anatomy and physiology

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Other evolutionary changes also occurred in the million years that it took for our ancestors to adapt to a fully terrestrial lifestyle.  For instance, their feet became stiffer, and their legs became somewhat longer so that they could travel overland more rapidly.  However, the evolution of their arms and legs was not as drastic as when their descendants became almost totally dependent on hunting for their sustenance.

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Their hands also evolved in shape and function, giving them a better grip on rocks.  They would likely throw rocks at predators, and they might have thrown rocks at herbivores so as to maneuver them into traps.  Sometimes, the hominins would use large rocks to smash bones, or they would break a rock in order to get a sharp cutting edge.  Their shoulder joints, in the course of time, moved somewhat to the side, making it easier for them to walk upright and to throw stones.

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There were also changes in the air passages by which air was drawn into their lungs and expelled.  This was because the hominins often wandered far from where water could be found; they needed to conserve water.  Consequently, evolution caused the sinuses in their heads to expand.  Their newly evolved external noses captured moisture and recycled it.

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All of these anatomical and physiological adaptations had begun several million years earlier, when succulent fruits had become seasonal in Eurasia.  Moreover, when hominins had begun to forage along the shoreline, they had evolved an ability to expel excess salt from their bodies.  Then, as they readapted to a fully terrestrial lifestyle, these changes were partially reversed − their kidneys, sweat glands and lachrymal glands were reduced in size and drastically reduced in function.

Terrestrial hominins also acquired superior visual acuity, because they needed to spot animals or bleached bones amidst vegetation or at great distances.  This involved not only enhancement of the optic nerve, but also brain refinements and changes in the vestibulocochlear apparatus in their inner ear in order to improve coordination between eye movements and head movements.

Onset of the Ice Ages

Kenyanthropus platyops were unable to survive the climatic changes that occurred in the Rift Valley of Africa prior to the first glacial maximum of the Ice Ages, about 2.6 million years ago, and the changing climate forced Australopithecus afarensis to rely more on tough, fibrous foods, so that they evolved gigantic jaws and jaw muscles.  But even more drastic climatic changes occurred in Europe.  Our own ancestors did survive the first great glacial maximum of the Ice Ages, most likely because they had moved south, into the Levant.

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Some of the hominins who moved into the Levant at this time moved still further south, into Africa.  These whose fossils have been found there by archaeologists have been named, respectively, Australopithecus sediba, Homo habilis and Homo rudolfensis, respectively.  Their characteristics will be examined in the next chapter.