The crop traffic matters for the towns and states it made possible

What holds the age of agricultural exchange together is what the exchanges did to social, political and ritual life. Each transfer added a crop or an animal to a farming system, raised its output, widened its diet and reduced the damage a single failed harvest could do. The consequences ran through the population. Better fed communities grew, growing communities settled closer together, and dense settlement forced people to work out larger villages, more elaborate kinship, more formal authority and more specialised trades. Over the following three millennia that arrangement produced cities, states and empires in several regions at once. Africa was one of the main theatres. The Middle Nile culture area, the rise of Qustul and the unification of Egypt belong to the same process that produced Mesopotamia, the Indus valley and the states of the Yellow River, and they were built on the same foundation of exchanged crops and exchanged herds.

The Levisa rock shelter in Cuba holds a Lithic age deposit dated to 4190 BCE. It is among the earliest confirmed human occupations anywhere in the Caribbean islands. The people who left it worked stone, took what they needed from the rivers and the high ground behind them, and moved with the seasons rather than settling in one place. They were foragers, and the way they lived has to be kept separate from the Taino societies that European ships met almost six thousand years later. Those were farmers with villages, chiefs and ball courts, and they came out of a different tradition. This matters for how the region gets narrated. A Caribbean history that opens in 1492 treats the islands as empty until Europe arrives. A rock shelter in Cuba dated to 4190 BCE says the islands had been occupied for something like six thousand years by then, which makes the usual starting point a decision somebody took.

Anthropologists building their discipline in the nineteenth century kept finding regions where peoples of quite different origins had spent centuries in contact and had come to share deep features of culture, well past the superficial. Upper Egypt and the eastern Sudan belt were such a region from the sixth millennium BCE onward. Ehret calls the long south to north stretch the Middle Nile Culture Area. The label changes the question of Egyptian origins. Egypt did not come out of one ethnic group or one language community. It came out of a zone of sustained interaction among peoples with different linguistic and historical backgrounds, who over thousands of years of contact built a common stock of practices, ritual forms and material traditions. That makes Egyptian civilisation a regional outcome. To follow it you have to look south, into Nubia and Sudan, because half the culture area lay there and so did the origins of much that museum labels now file as distinctively Egyptian.

In the matrilineal societies spread right across Africa's southern savanna belt, a young man who wanted to marry applied to the mother of the woman and to her mother's female relatives, acting as a group. Their consent was the one that counted, ahead of her father's and ahead of her mother's brother's. To win it he performed bride service, working for months and sometimes for several years under their direction. After he was accepted and married he was still required to show marked deference to his mother in law for the rest of her life. Marriage is the central economic and reproductive transaction any society makes, and here the women of the lineage controlled it. They judged the suitor, set the labour, and admitted him or refused him. The practice turns up in societies speaking languages from deep and separate branches of Bantu, which puts it in place long before those branches parted. For thousands of years, across a third of the continent, this was ordinary.