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But when the agricultural villages of the Neolithic expanded into larger towns that grew to more than two thousand inhabitants, the capacity of the human brain to know and recognize all of the members of a single community was stretched beyond its natural limits. Nevertheless, the tribal cultures that had evolved during the Upper Paleolithic with the emergence of symbolic communication enabled people who might have been strangers to feel a collective sense of belonging and solidarity. It was the formation of tribes and ethnicities that enabled the strangers of the large Neolithic towns to trust each other and interact comfortably with each other, even if they were not all personally acquainted. The transformation of human society into urban civilizations, however, involved a great fusion of people and societies into groups so large that there was no possibility of having personal relationships with more than a tiny fraction of them. Yet the human capacity for tribal solidarity meant that there was literally no upper limit on the size that a human group could attain. And if we mark the year 3000 BC as the approximate time when all the elements of urban civilization came together to trigger this new transformation, it has taken only five thousand years for all of humanity to be swallowed up by the immense nation-states that have now taken possession of every square inch of the inhabited world. The new urban civilizations produced the study of mathematics, astronomy, philosophy, history, biology, and medicine. They greatly advanced and refined the technologies of metallurgy, masonry, architecture, carpentry, shipbuilding, and weaponry. They invented the art of writing and the practical science of engineering. They developed the modern forms of drama, poetry, music, painting, and sculpture. They built canals, roads, bridges, aqueducts, pyramids, tombs, temples, shrines, castles, and fortresses by the thousands all over the world. They built ocean-going ships that sailed the high seas and eventually circumnavigated the globe. From their cultures emerged the great universal religions of Christianity, Buddhism, Confucianism, Islam, and Hinduism. And they invented every form of state government and political system we know, from hereditary monarchies to representative democracies. The new urban civilizations turned out to be dynamic engines of innovation, and in the course of just a few thousand years, they freed humanity from the limitations it had inherited from the hunting and gathering cultures of the past.
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Richard L. Currier (Unbound: How Eight Technologies Made Us Human and Brought Our World to the Brink)