SAPIENS

Brain remodeling

​

Our ancestors have gone through at least three episodes of self-domestication in the course of their evolution, and each episode caused infants, children and even adults to retain immature brains and immature behaviors.  For most animals, a long period of immaturity would be reversed in the normal course of evolution, but our ancestors (in part) failed to experience these corrections.  This was because long periods of immaturity were vital to our ancestors, enabling them to pass on knowledge, skills, and especially linguistic competence from one generation to the next.

​

The brains of all animals, especially mammals, are remodeled early in life; neurons and neural connections that are little used are pruned, new neurons sprout to help out those neurons that are overworked, etc.  This ensures that the animals, as they mature, will become better able to handle the demands that are placed on them.

Our ape ancestors, more than most animals, depended on this brain remodeling to enable them to find the very special foods that they needed, and when our ancestors began to develop linguistic competence, this early brain reorganization was put to work at a new task:  custom-designing the brain during infanthood so as to enable adults to correctly understand the language into which they had been born.

​

The long immaturity of infants and children, brought on by episodes of self-domestication, were not reversed, because the long periods of immaturity enabled the brain to be more extensively remodeled early in life, enabling infants to learn more complex and extensive languages.

In this section we will examine some new requirements for linguistic competence that confronted our Group A ancestors in the swamplands of the Middle East but first let us examine some common assumptions.

Concerning some popular assumptions

Lots of archaic human fossils found in Africa have been dated to between 700,000 and 400,000 years ago, but as the magic date of 320,000 years ago approaches (in the archeological record) 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 the earlier African fossils -- compressed face, tall cranium and sharp chin -- evolved directly  from the quite different features (and corresponding patterns of growth) of the earlier Africans, 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.

​

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 but then almost entirely wiped out, presumably by Sumerian farmers.  We will deal with that later.

We might entertain the possibility that Homo sapiens evolved directly from a subset of the earlier African population, except that (in light of new genetic evidence) we would have to explain how this subset of the population had remained separated from the rest of the Homo heidelbergensis population for more than a million years prior to that.

Alternatively, it could have been Group B rather than Group A that came into Africa 300,000 or so years ago.  But the only new hominin species other than archaic Homo sapiens that shows up in the African fossil record about 300,000 years ago is Homo naledi.  If I were to bet, I would put my money on archaic Homo sapiens being the source of the other part of our ancestry.

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, and I suggest that they came from the Middle East.​​​​​​​​​​​​​​​​​​​​  Most current researchers make wild assumptions about what happened in the late Middle Pleistocene, between 300,000 and 120,000 years ago, simply because so little is known about it, but  seems to ignore everything that occurred prior to about 200,000 years ago, because events that are further back than that are very hazy, but we shouldn't just assume that the crucial events in our evolution were not further back in time.  And indeed, it was right around 300,000 years ago that archaic Homo sapiens suddenly appears in the fossil record in several places around Africa.

​

Incidentally, reexamination of a fossilized skull found at Broken Hill in what is now Zambia and identified as Homo rhodesiensis and then Homo heidelbergensis has been redated at about 300m000 years ago, and reexamination of the skull indicates that it most likely belonged to a population that was ancestral to both Homo neanderthalensis and Homo denisova.  Based on this appraisal and other factors neither of the earlier identifications seem appropriate, so I will call the species represented by this individual the Broken Hill Homo.

Descendants of the Broken Hill Homo seem to have survived in the Levant ​until about 130,000 years ago and their fossil remains were found at Nesher Ramla in central Israel.  Stone tools that they had produced were found nearby, and both the fossils and the tools were dated to roughly 130,000 years ago.

These new findings fit with the narrative that I have outlined but the commonly accepted narrative about a simple evolution of earlier African populations into Homo sapiens is contradicted by recent genetic findings.

The origins of Homo sapiens

As I have noted, our direct ancestors split into two groups, which I call Group A and Group B, about 1.4 million years ago.  After that, the effective population of Group A was drastically reduced in size but then slowly rebounded.  During and after the rebound in population of Group A mostly stayed in southern Mesopotamia, but about 400,000 years ago some of them moved into Africa, where they eventually recombined with survivors of Group B.  Based on this narrative, we can now identify the other part of our ancestry -- the part which split from Group A about 1.4 million years ago and then recombined with them 300,000 years ago.  They were none other than the ancestors of Homo neanderthalensis and Homo denisova.

Analysis of modern human DNA indicates that after Group A recombined with Group B much of the Group B part was eliminated in the course of time, especially that part that coded for proteins, built structures, or turned those genes on or off.  This indicates that our inheritance from Group B, even though it constitutes only about 20% of the DNA in our genome, had originally constituted a much greater part of our ancestors' genome -- much of that DNA was incompatible with our inheritance from Group A and was subsequently eliminated.  Not only has much of the DNA from Group B disappeared from our genome but that part that is now left is probably the least effective part of what we originally inherited from them.

Percussive signals

Let us now return to our narrative about our Group A ancestors in the vicinity of the swamplands of southern Mesopotamia.  There, they continued to hone the communication skills and social skills that they needed in that very special environment.  In particular, they needed to evolve both socially and genetically so as to extract the maximum value from the percussive signals that they used for tracking down hippopotami in the swamplands.  This involved the invention of ways to transmit more precise information by means of percussive signals and to promote cooperation among hunting groups that often spoke mutually unintelligible languages.

​

Percussive signals enabled our ancestors to organize and cooperate on a larger scale than hominins who had moved elsewhere after the "bottleneck" in the population of our Group A ancestors.  Even more crucial than the advantage that use of the signals provided in tracking the movements of hippopotami, use of the signals forced our ancestors to develop a special talent for decoding information that is coded sequentially.

​

This is because spoken language had almost always been 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 cannot combine the percussive signals (which are coded sequentially) with gestures (which can more easily convey three-dimensional information).

​

As I noted, 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.

​

A gestural language can easily convey spatial concepts by means of hand or body movements, while spoken language, without gestures, can require visualization skills which our ancestors did not have.  This shortcoming in visualization arose when they needed to convey three-dimensional information by means of sequentially coded information that was not accompanied by gestures.  This is because gestures, which consist of hand and body movements, can be three-dimensional in their very nature.

​

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 often unable to do so if (in the absence of a sophisticated gestural language) they are born deaf, or for some other reason have little or no exposure to a modern language.  But the conveyance of three-dimensional concepts by means of percussive signals was so important to our ancestors that in the course of hundreds of thousands of years our Group A ancestors who stayed near the swampland until relatively recent times did evolve this important capability.

​

The use of percussive signals 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 served as aa lingua franca in such cases.

​

Hand axes in Arabia

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.  Eastern Africa was not to the liking of the new immigrants, so most of them turned around and returned to southern Mesopotamia, but some of these newcomers explored Africa, looking for something better.

Some of the immigrants explored to the south, where they found both hippopotami and elephants.  Likewise, others found their way into the Nile Valley and found hippopotami and elephants there.  But the indigenous people in both places were so hostile that the newcomers settled for Central Africa.

We know about this early influx into Africa because our ancestors left calling cards on the Arabian Peninsula -- hand axes that were handy for slicing up hippopotami but were unnecessarily heavy when chasing down the smaller game of Africa.

​

A few thousands of years after this wet period, rainfall declined on the Arabian Peninsula and dry conditions prevailed until wet conditions returned about 300,000 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 left their calling cards along the way -- hand axes that were somewhat smaller and sharper than those that had been left there a hundred thousand years earlier.

This time it was somewhat different, because eastern Africa had become very dry, and this had emptied the region of the indigenous population and archaic Homo sapiens had come into the region from Central Africa. so instead of exploring further afield, those who had recently crossed the Arabian Peninsula joined the indigenous Homo sapiens population in eastern Africa and simply took over the Rift Valley of eastern Africa.  Although the region was very dry, there were many lakes in the Rift Valley of eastern Africa and the rough country there provided many opportunities for trapping and slaughtering animals.

Sudden appearances around Africa

Our Homo sapiens ancestors -- by this time most likely carrying some DNA picked up from the Broken Hill Homo -- also began showing up in other parts of Africa about 300,000 years ago because their population had been increasing in Central Africa throughout the hundred-thousand years between the two influxes into Africa.  The earliest evidence of this population buildup has been found in Morocco where fossils of early, archaic Homo sapiens have been found, and dated to around 315,000 years ago.  Along with fossils archaeologists found their stone tools, which were smaller and lighter than hand axes but convenient for butchering the gazelles and zebras that they found in Morocco.

From around 300,000 years ago archaic Homo sapiens begin to show up in the archaeological record at various sites in Africa -- they spread out in every direction from Central Africa, most notably to the northeast into the Nile Valley and to the southeast into what is now Zambia.  They undoubtedly pushed aside the indigenous Broken Hill Homo in order to take over that valuable territory but also interbred with them.

Stone-tool innovation flourished especially in Central Africa. because that was where their population was centered, and they proved to be much better than the Broken Hill Homo at maintaining social and trade networks that spread innovations throughout their African population.  This was partly because of their ability to communicate while still at a distance, by using percussive signals.