Surplus wealth meant surplus people. As productivity rose, not everyone needed to farm, so new social roles appeared. Many people became vagrants or slaves, but other nonfarmers ended up controlling much of society’s surplus wealth because they could specialize in useful social roles. They could become full-time priests or potters or soldiers or philosophers or rulers. Specialists became expert at their limited roles. But the division of labor also created new forms of dependence. As social roles multiplied, human societies, like the first metazoans, became more networked, more differentiated,
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