EURASIANS

Eurasian hominins

​

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 and physiology.

​

Domestication syndrome

​

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.

​

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 groups these Eurasian terrestrial hominins tended to become isolated from other groups, and conequently they tended to become inbred.  Thus, evolution took a much different turn in Eurasia than in Africa:  a scattershot of local characteristics arose in Eurasia, and among these was an evolutionary shortcut known as domestication syndrome.

​

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.

​

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 relatively successful, compared to those in which a dominant male weeded out his competitors in the group, and eventually such groups came to replace other wandering groups in the total population.

​

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 -- the hominins were often 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.

​​

The ancestors of these newly terrestrial hominins had often trapped and slaughtered quadrupedal 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 to retain mature males in their foraging groups.  Yet their foraging groups needed to be small enough to live on the small amounts of bone marrow that were 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.

​

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 more experienced adults, but also because it favored ​cooperative and playful behaviors.

​

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.

​

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​

​

Whenever a small or large predator was spotted, our terrestrial ancestors passed the word by tactile contact and/or by facial or hand signals 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.

One of the earliest and most important of these signals was eye movements.  This was probably the time when our ancestors evolved to have white sclera, which made it easier for members of the group to locate the direction of a person's gaze.  This capability was so important that an inbuilt reflex, originating in the brain stem, for signals that identified threats.  The reflex for these signals, as well as the ability to effortlessly identify their meanings, was so important that it has been passed on to us, their direct descendants living today, more than three million years later.  These signals have been preempted and modified by later evolution for subtle non-vocal social communication.

​

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, to signal intentions, and to coordinate various group 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 hominin societies, use of weapons and the hominin 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.

​

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.  Complex hand signals were precursors to complex vocal signals, and this conclusion is confirmed by the close connections in the brain between intentional communication by hand signals and intentional communication by vocal signals.

Anatomy and physiology

​

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 legs and especially their arms was was not as drastic as when their descendants became more dependent on hunting for their livelihood.

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.

​

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 also captured moisture and recycled it.

​

All of these anatomical and physiological adaptations had begun several million years earlier, when succulent fruits had become seasonal in Eurasia.  Moreover, when hominins begun to forage along salt-water shorelines this sometimes prompted to evolve an enhanced 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.

Encephalization

Thus, rapid evolution of the brain was needed in order to acquire improved visual acuity, and this was accomplished by loosening of controls on proliferation of neurons in the early stages of pregnancy as well as in later stages of development.  This process was similar to that involved in development of domestication syndrome, in that it was based largely on delayed development of certain precursor cells.  This was the start of a trend of increasing brain sizes that has continued almost to this day.  This continued process of brain enlargement served different purposes in different stages of our evolution.

The increased proliferation of brain cells often resulted in proliferation of cells that did not exactly match the particular cells that needed to be proliferated, and this was corrected in a more gradual evolutionary process of fine tuning the process through further evolution.  Thus, the encephalization that occurred was in excess of what was needed in order to accomplish the desired enhancement of visual acuity and interpretation.  While this rapid encephalization was later modified by pruning it was never fully reversed and has continued almost to this day.  We will revisit this subject in later sections.

XXXGroup vocalization and celebrationXXX

XXXAs Eurasian hominins adjusted to new opportunities and challenges they diverged from their ape relatives.  Still another divergence was their greater inclination to change their behavior in response to special conditions that arose.  For example, their closest living relatives, chimpanzees and bonobos have set behaviors, relative to finding mates:  Male chimpanzees will sometimes join in group vocalizations in order to attract females, but bonobos are led by female matriarchs, and males have to come looking for mating opportunities.  And a male gorilla will sometimes bang on the trunk of a tree, and male orangutans sing.  But hominins in the line of evolution that eventually led to modern humans were more inclined to take advantage of special circumstances.XXX

XXXOnce hominins perfected group defense, acquisition of the carcass of a large animal would provide an opportunity for both males and females to acquire mates to which they were not related, so when a large carcass was acquired this might be an occasion for group vocalization in which both sexes participated.  The resulting celebrations were likely a prelude, in the course of time and evolution, to singing, dancing and percussive signaling.XXX

XXXOnset of the PleistoceneXXX

XXXKenyanthropus platyops were unable to survive the climatic changes that occurred in the Rift Valley of Africa prior to the glacial maximum that marked the began the Pleistocene epoch about 2.58 million years ago, and the changing climate forced Australopithecines 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 that first great glacial maximum, by moving into Africa.  This is shown by the early Homo fossil found at the Ledi-Geraru site in the Afar region of Ethiopia and dated at about 2.8 million years ago.XXX

XXXThe Homo fossils found at the Ledi Geraru site include only a jawbone and teeth, so the species can't be named, but the fossils definitely belonged to a member of the Homo clade.  Like other members of the Homo clade, the Ledi Geraru Homo most likely had evolved in Eurasia prior to moving into Africa.XXX

XXXFurther south along the Rift Valley, in Kenya, archaeologists have found the tools that were made and used by these early.  The tools included sharp flakes and hammerstones, and the archaeologists also found rock cores from which flakes had been expertly struck.  More than a thousand of these stone artifacts have been found in northern Kenya, showing that these earliest African consistently made these tools over a period of 300,000 years, at a time that preceded the increase in brain sizes, indicating that increased brain size was not needed for the production of such tools.XXX