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

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 Not Just in Numbers but 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 not the subsistence exchanges alone but their cascading consequences 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 not of sudden revolution but of incremental accumulation, each new crop or technique widening the margin between survival and abundance. This increased productivity enabled agricultural populations to grow — and to grow not merely in overall numbers but 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 — not later, not derivative, not borrowed. 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.