So powerful was the shock from linking the different world zones that, within just a few centuries, human societies had crossed the eighth threshold of increasing complexity. The change was fast because it occurred in a globalized world. In the past, collective learning had worked at local or regional scales, which is why it took ten thousand years for farmers to spread around the planet. In a world of global networks, it took just a few centuries to transform much of Earth. This was a change as momentous as anything that had happened in the entire four-billion-year history of the biosphere.
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