6000–3000 BCE: (The Social Consequences of Agricultural Exchange: New Crops and Domestic Animals Enriching Productivity, the Proportion of Diet from Cultivat…

6000–3000 BCE: (The Social Consequences of Agricultural Exchange: New Crops and Domestic Animals Enriching Productivity, the Proportion of Diet from Cultivation and Herding Progressively Growing While Foraging Declined, Population Growth in Numbers and in the Size and Density of Residential Groupings, and in a Few Regions the Emergence of Larger and More Centralized Political Formations): What gives coherence to the era of agricultural exchange is the cascading consequences of the subsistence exchanges for social and cultural history. As new crops and domestic animals moved between regions, they enriched the productivity and variety of agricultural practices wherever they arrived. The proportion of the diet derived from cultivation and herding progressively grew while the proportion coming from collecting and hunting declined, a transformation of incremental accumulation, each new crop or technique widening the margin between survival and abundance. This increased productivity enabled agricultural populations to grow in overall numbers and in the size and density of their residential groupings, and in a few regions late in the era, in the scale and centralization of the political formations to which people belonged. Here was the material foundation for everything that followed: the towns, the kingdoms, the trade networks, the specialized crafts, the religious institutions. And it was a foundation laid across Africa in the same broad periods as across Eurasia. The social complexity that European observers would later declare absent from African civilization was being constructed in these millennia, brick by agricultural brick, long before Europe itself had moved beyond the most rudimentary farming.