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, this immaturity would be reversed in the normal course of evolution, but our ancestors 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 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 and more complex and extensive languages.
The modern mind and the cerebellum
In some places, including along the southern coast of Africa, settled life persisted for a very long time, maybe for one hundred thousand years or longer, and the languages spoken there became more and more complex and extensive over time. More complex and extensive languages, in turn, enabled each generation to acquire the knowledge and skills that were demanded by their increasingly complex societies. The brain remodeling that enabled infants and young children to acquire the more complex and extensive languages serendipitously created the Modern Mind.
The modern mind was largely a product of cultural evolution, but in places and times when the modern mind emerged, this stimulated rapid evolution of a primitive structure deep in the brain that choreographed the activities of muscles throughout the body. This seems counterintuitive, but rapid evolution of the cerebellum was impelled by the increased importance of learned skills in modern societies.
This new spurt of human evolution was impelled by division of labor. The division of labor in human society was not new, but it was accentuated by the arrival of modern times; in modern times, not only was the best hunter not necessarily the best workman, but neither was he the best planner of the hunts, the best organizer of the hunts, the best story-teller, or the most powerful shaman. In each specialty, however, the activities of the specialist were coordinated by his cerebellum.
All of this was encouraged by larger societies: larger societies made possible the emergence of higher-order specialties, as well as new levels of governance and decision-making such as gatherings of elders.
Further evolution of the cerebellum has had consequences that went far beyond the performance of tasks, because the cerebellum is involved in interactions with people as well as with things, and social interactions are somewhat different in different cultures. When differences between cultures cause discrepancies to arise between what is expected and what is experienced, this can lead to conflict or war. On the other hand, further evolution of the cerebellum in the last fifty thousand years or so has enabled the development of new ways to avoid violent conflict, such as democratic governance, voluntary submission to government authority, and general agreement on proper conduct, and these promote stability and peace.
Expansion of the cerebellum, has affected the shape of the modern human skull: As the larger cerebellum matures within a developing human fetus, it pushes out in every direction from its central location in the brain, and causes the skull to become more globular in shape, and this shaping of the skull continues after birth.
Self-domestication and modernity
Tribal societies, besides helping our ancestors to take over Africa, affected them more directly: institutions of government, such as councils of elders sometimes imposed penalties on their members, such as ostracism. By imposing such penalties, which could affect an individual's ability to procreate, tended to weed out individuals with a tendency to react violently, and this amounts to selection for tameness, the precondition for domestication syndrome to appear in the population, because the least reactive individuals in a population tend to be those in which precursors to fetal neural cells and certain other kinds of cells (such as pigment-producing cells and bone-producing cells) are delayed in their development during the embryonic stage of development. The delayed development of the neural cells then results in immature behaviors, like a less reactive personality, to persist even into adulthood, and the delayed development of other kinds of precursor cells can result in anatomic and other consequences.
For example, if precursor cells to pigment-producing cells do not fully mature, the pigments produced by the pigment-producing cells may be altered, and if there are fewer bone-producing cells as a result of the slower maturation of the precursor cells, the skeleton may not be fully developed even in adulthood. In this case, the suite of characteristics is called self-domestication, because it was not caused by the activities of an outside agent.
domestication syndrome is observable in domesticated animals, which tend to be tamer than their wild counterparts but also tend to have altered coat colors and rounder heads.
Like all inherited characteristics, the behavioral and other changes can subsequently be modified by selective pressures. For instance, slow maturation of pigment-producing cells can alter or reduce the number of pigment-producing cells in the skin, hair or eyes. But the eyes of newborn infants are particularly vulnerable to damage by ultraviolet light from the noonday sun, especially in the tropics, and reduced or altered pigmentation can make their eyes even more vulnerable to damage. Such damage to the eyes can reduce their viability later in life, and this can lead to positive selection for those whose eyes are better protected by pigmentation.
We might note in this connection that many modern people whose ancestors lived along the northern coast of western Europe have retained the varied eye colors of their ancestors. This is because oceanic and atmospheric conditions melted the glaciers along the Atlantic coast, and this enabled large numbers of people to live far to the north, where sun does not rise so high in the sky, and where ultra-violet light is filtered out as it passes through the atmosphere at shallow angles. Moreover, infants lying on their backs are less prone to being blinded from staring up at the noonday sun, if the sun does not rise so high in the sky. Thus far-northern people with blue eyes were less vulnerable to eye damage and blue eyes were retained in far-north people.
Incidentally, reduced skin pigmentation was favored in the far north for another reason altogether: heavy pigmentation of the skin reduced exposure to the sun’s rays of deeper layers of the skin, where Vitamin D is produced. Slowed maturation of these cells caused altered skin pigmentation, and this altered pigmentation was retained among far-north people, who benefitted from it.
Other accidental consequences of slowed maturation at the embryonic stage of development were also retained in the far north, as well: lightened hair pigmentation tended to be retained as well, and baldness at birth. Freckles and red-colored hair were sometimes retained, as well. Some of these symptoms of self-domestication faded rapidly, especially in the tropics.
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