HOMO

The switch to vocal languages

After the first glacial maximum had passed, European hominins, our ancestors among them, gradually

increased in size, making them less vulnerable to

predation.  This allowed them, over the course of the next million years, to gradually combine their gestural language with vocal elements.

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Gestures can more easily convey emotional responses, such as surprise, as well as spatial relationships and plans of action, but vocalization can alert an entire group of hominins to something that is happening.  This is undoubtedly one reason why hominins began to combine gestures with vocalization.

Vocalization ensured that everyone was fully aware ofwhat was going on, so it began to be used in parallel with gestures, but then another advantage of vocalization began to assert itself:  Vocal language is more accessible to infants and young children, while their brains are still maturing.

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The switch to vocal languages was not a simple one, because vocal languages are structured linearly -- words are built out of linear strings of phonemes, and sentences are built out of linear strings of words.  The patch of brain tissue that is in charge of building and decoding the linear structure of vocal speech is called Broca's area, and it is located on the left side of the motor cortex, which is near the front of the brain.

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Broca’s area was strategically located, in the part of the motor cortex that coordinates muscle movements of the lips and tongue.  These muscles, of course, are responsible in large part for producing the phonemes of speech.  (In general, the left side of the motor cortex

coordinates muscle movements on the right side of the body, but muscle movements of the lips and tongue, in the middle of the body, are coordinated by a patch of brain tissue that is located on the left side of the brain.)

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By observing imprints left by the brain on the inner surfaces of fossilized skulls, scientists have been able to determine that hominins who lived about 1.8 million years ago were still using gestural languages --  their neocortices did not have the extra fold that later resulted from expansion of the patch of brain tissue where Broca's area was located, near the front of the cerebral cortex and on the left side of the brain.

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This patch of tissue needed to expand to accommodate memories of how to pronounce the phonemes and string them together into words and sentences.  It also needed to coordinate with other parts of the brain that put together strings of words and sentences so that they could convey messages.

In order to do all of this, Broca's area (located on the left side of the cerebral cortex and a little to the left of the center line) had to expand.  This expansion pushed one more crease into the surface of the cerebral cortex, which left an imprint on the inner surface of the cranium.

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In the course of the next million years or so, the imprint of this extra fold gradually shows up on the inner surface of the cranium, but this evidence of vocal speech is contradicted by another piece of evidence:  the dimensions of fossilized inner-ear structures were such that the hominins could not have heard consonants.  Consequently, vocal speech must have been based almost entirely on vowel and tonal sequences and stops until later in our evolution when our more recent ancestors perfected a purely vocal form of communication that could quickly convey complex information.  (Homo neanderthalensis could hear consonants, but not as easily as Homo sapiens.)

Brain size

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The remarkable increase in the brain sizes that has occurred among most members of our genus in the course of the last two million years or so is something that needs to be explained somewhere in the story of human evolution, and it is becoming clear that two factors working together jumpstarted the process, starting more than two million years ago.

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The first and earliest factor was bipedalism.  Obviously, bipedalism did not by itself bring about any great brain expansion, because our ancestors have been bipedal for at least eleven million years; but about five million years ago, when our ancestors became fully terrestrial, and their hips narrowed, so as to enable them to walk more efficiently.

This adjustment narrowed the opening through which the birth canal had to pass, and since it was difficult or impossible for the head of a fully mature fetus to fit through the narrowed opening, birth had to occur while the infant was immature and still helpless.  This forced changes in family structure; but still, brain sizes did not increase greatly at that time.

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The second factor seems to have made its appearance between two and three million years ago when gestural language developed to the point where the hunting skills of our ancestors began to match those of other predatory animals; -- not only in the case in which two-legged semi-aquatic hominins drowned competitors and prey alike but also in the case where slow-moving but smart hominins constructed weapons and devised plans of action that would enable them to match the prowess of predatory animals whose skills had been honed by evolution.

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Our ancestors could not afford to wait millions of years for evolution to give them the brain power to accomplish this feat; they needed a quick fix.  That quick fix was to discard many of the controls on proliferation of neurons in the brain and let neuron proliferation run rampant.  In their small, highly inbred groups, a single member with just the right kind of neuron proliferation could give the group a hunting or communication advantage.  With luck, this new skill would spread throughout the group, and a new species would appear on the scene in the course of a few generations.  This rapid evolution would eventually enable us to master the entire globe, for better or for worse.

Return of ​Homo to Eurasia

Our ancestors moved into Africa prior to the fist great glaciation of the Ice ages, which reached its climax about 2.58 million years ago but some of them quickly moved back thereafter as shown by crude stone tools in northern Jordan − flakes that our likely ancestors had struck off from a rather large rock about 2.5 million years ago.

By the time they returned to Eurasia about 300,000 years had elapsed since they had abandoned Eurasia for the tropics, and they had developed new cognitive and social skills that better suited them for trapping medium-sized animals such as small deer and for claiming carcasses from large carnivores such as leopards.  Still, some of them returned to their old habit of wandering about in search of bleached bones, because this allowed them to remain in compact groups, where they were less vulnerable to predation by leopards.  (Hunting other animals required them to spread out as they sought to trap their own prey.)  Others looked for the best hunting grounds, and they found them at the base of the Tibetan Plateau, where water constantly trickled down from the high plateau to the Loess Plateau, which was much further down, creating deep gulches and ravines where animals such as deer and antelope could be easily trapped.  Homo occupied the region continuously from 2.12 million years ago to 1.26 million years ago, but we know this only because their stone tools have been found at the base of the cliffs at the northern edge of the Tibetan Plateau, at the northern edge of the Loess Plateau.

No hominin fossils were found there, but three thousand miles to the west, in the Republic of Georgia, hominin fossils, crude stone tools and butchered bones have been found at a site in the Republic of Georgia.  The fossils, dated at about 1.8 million years ago are now commonly called Homo georgicus.  These remains were 140,000 years younger that the oldest stone tools found near the base of the Tibetan Plateau, so at least that much time had elapsed since Homo had returned to Eurasia.  Obviously, they had to returned to Eurasia to stay awhile.

Homo georgicus were somewhat smaller in size than their contemporaries in southern Africa, perhaps because many of them did simply wander about in search of bleached bones, and otherwise relied on low-quality foods -- when they couldn't find suitable bones that hadn't been broken.  This reduced their vulnerability to predation, so that they didn't need to have such large body sizes, and it didn't require them to outsmart faster-moving animals in order to trap and slaughter them.  This might account for the variation in head sizes.

If the Homo georgicus population were a founder population that had recently migrated from Africa we would not expect to find so much variation among its members.

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The fashioning of garments?

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Those whose fossils were found in Georgia may have already begun to practice the art of tailoring. but they also needed to learn to wear garments, and to take care of them.  Inclinations to do all of these things are observable in the behavior of modern humans.

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For instance, the maternal concern that prompts modern human mothers to make or buy clothing for their children is like the maternal concern that prompted ancient human mothers to make good garments tor their offspring.  Moreover, cultural norms prompt us to wear clothing or to wear tattoos or other body ornaments that define us.  The pride and sense of identity that we feel when we display fine clothing or jewelry on our bodies are like the behaviors that prompted our early ancestors to take care not to lose their garments, regardless of whether or not body coverings were immediately needed in order to keep warm.

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The behavioral changes of making and wearing garments did not come easily to our ancestors because those behaviors had not been part of the behavioral repertoire of their own ancestors − the behavioral and the ideational changes that enabled our ancestors to make and wear well-fitting garments were acquired through genetic as well as cultural evolution.

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In any event, it is doubtful that these ancient Eurasian hominins could have produced well-fitting garments without better tools, and even more doubtful that they would have been able to resist the temptation to discard their garments the minute the weather improved.

Control and use of fire?

Likewise, the value of learning to create and control fire was something that dawned slowly on our ancestors.  Once they recognized the value of fire, a long search then ensued for ways to create fire, and this search continued for hundreds of thousands of years, until the invention of matches and cigarette lighters.

The first use of fire was the opportunistic exploitation of the bounty that followed in the path of natural fires.  The remains of animals that had been caught in wildfires furnished lots of meals, so one of the first uses for intentionally set fires was to intentionally set such wildfires.

Another early use of fire was to preserve meat so that it could be used for a longer period of time.  This was probably done by slowly smoking the meat.  Then if hunting expeditions failed to result in fresh kills, the hunters might not go hungry.  This use of fire prevailed for hundreds of thousands of years.

Homo erectus sensu lato

Homo georgicus was the first named representative of a series of closely related species who are known collectively as Homo erectus sensu lato.  Many of these species moved along the coasts and along the river valleys of Africa, South Asia and Southeast Asia between two million and one million years ago.  Like Homo georgicus they had little incentive to fashion and wear garments and never were able to tolerate cold temperatures, probably because they wore no garments.

Only those members of the Homo clade who stayed mostly in relatively cold northern regions and retreated to the tropics only during severe glaciation at the North Pole had an opportunity to contribute substantially to our ancestry.  This included most members of the Homo clade who are commonly subsumed under the Homo erectus sensu lato rubric; but Homo georgicus probably did contributed substantially to our ancestry.

In Southeast Asia some Homo erectus hominins readapted to finding much of their food by diving into the sea, and they may have re-evolved an ability to expel large amounts of salt from their bodies through their kidneys, sweat glands and tear ducts.  This may have helped some of them to reach Luzon in the Philippines and helped others to reach Flores Island (now known by another name) in Oceania.  These island dwellers evolved to be very small -- a condition known as island dwarfism which also affected elephants that reached Flores Island.

Homo antecessor and an unnamed species

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After the first great glacial maximum, about 2.58 million years ago, climates in Eurasia again warmed; grasslands opened up in places allowing herbivores from Africa and Asia to drift into Europe, and the herbivores were followed by carnivores and humans. These movements came in waves, as the climate warmed and cooled, and with each successive cooling period there was a die-off of the humans in Europe.

Stone tools and other artifacts left behind by these humans have been found in many places in Europe, from southern Spain and Italy to Britain.  Moreover, some fossils of early European hominins have been found.  Facial bones dated at about 1.1 million years ago have been found in a cave in the Atapuerca Mountains of northern Spain, and many fossils of a different human species, dated at about 900,000 years ago, have also been found in the region.  (These bones were well preserved in karst caves.)  The humans in the later of the two waves of immigrants to the region have been named Homo antecessor.

It has been suggested that Homo antecessor came clear from Africa, by following animals that migrated from there, but northern Africa had been largely emptied of hominins by dry conditions.  Moreover, no fossils at all like them have been found in Africa.  These early European hominins more likely came from the east; perhaps from what is now Ukraine, where stone tool manufacture and use occurred about 1.4 million years ago.

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Although Homo antecessor later drifted into extinction, their fossils display features that indicate that they must have been closely related to ancestors of many later hominins, including Homo heidelbergensis, Homo neanderthalensis and -- most importantly -- Homo sapiens.  Homo antecessor were not, however, in the direct line of descent between Homo georgicus and Homo sapiens.  This is indicated by genomic data.  Instead, they apparently drifted into extinction.

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The fossils of Homo antecessor show signs of periodic malnourishment which might have been associated with seasonal migrations of some of the animals they hunted.  In fact, these hominins may have tried to hibernate during periods when some the animals they hunted were in short supply.  The fossils that have been found show signs of cannibalism, perhaps by a rival hunting group.

The worn condition of their teeth may have resulted from chewing on the hides of animals in order to soften them or to draw sustenance from them, and severe chipping of their teeth may have resulted from trying to draw sustenance from the roots of wild vegetation that they pulled from the soil with dirt clinging to them.

Homo antecessor did not use fire, and that was surely one of their great failures.  They concentrated on killing small deer and other animals that would last a small group of hominins for only a few days, and without fire they had no incentive to accumulate an abundance of food, because they could not preserve it.  If hunting was poor they could only eat each other, and that is what they did.

Middle Eastern and African refugia

Homo antecessor had separated from our direct ancestors about 1.5 million years ago by following animals that moved north from Africa and west from Asia at this time, due to changing climatic conditions, and followed them into Europe.  But then as climatic conditions worsened, with further ice buildup at the poles of the Earth our own ancestors moved south from the Black Sea region and separated into two groups, Group A and Group B.  As the climate grew still colder, Group A found their way south to tropical swamplands that they found in southern Mesopotamia while Group B followed the Rift Valley south or moved along the coast into Africa.  The Rift Valley was a particularly attractive route, with lots of lakes along the way and rugged country where animals could be trapped.  We are descended from both of these groups, but primarily from Group A

Group A was reduced to a relatively small effective population about this time -- of only about 1,200 individuals -- who had found their way down one of the rivers that even then flowed south through Mesopotamia to a swampy delta.  They found an environment in southern Mesopotamia for which they were quite unprepared, but they managed to survive there for a million years before recombining with Group B.