Africa's most consequential export was a pack animal

A long list of crops and one animal of northeastern African origin began moving into Eurasia between 5000 and 3000 BCE, and the flow widened from 3000 BCE onward. The animal was the donkey, and it may have mattered more than everything on the plant list. It made overland carriage of goods and people workable across distances that porters could not sustain, which is the precondition for a caravan route. The trails that later linked Egypt to Mesopotamia, and West Africa to the Mediterranean, all ran on it. Ehret adds a further claim: the donkey may have been the model for putting the horse and the camel to the same use, in which case Africa supplied Eurasia with the idea of the beast of burden along with the first one. In the Americas the comparable transfer came later, when maize, beans and new squashes reached the Eastern Agricultural Complex of the present-day central United States during the first millennium BCE.

Barrera-Mordan, in the Dominican Republic, is one of the sites that forced archaeologists to move the date of human arrival in the northern Caribbean. The material there is a stone-working complex built on flaked tools struck from cores, and it dates to around 4000 BCE. The people who made it belong to what is labelled the Lithic age. They had no pottery, and they should not be confused with the ceramic-producing groups who reached the islands thousands of years afterwards and are far better known. What the assemblage records is a specialised adaptation, worked out for a set of islands with particular stone, particular coastlines and particular food. Sites like this are how the initial migration routes from the surrounding mainland get mapped, because the tool types are the trail. Hispaniola, the island Haiti shares, was inhabited about six thousand years ago by people who knew exactly what they were doing with rock.

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.

Loom weaving is the mechanical line of technological descent, and cotton is where it shows most clearly at a global scale. The machine looms of modern industry evolved from methods that begin in the middle of the Holocene. People invented cotton weaving independently in at least three parts of the world and possibly four. The proof lies in the plants. Each set of inventors domesticated a cotton species native to their own region: Gossypium barbadense in Peru, Gossypium hirsutum in Central America and Mexico, and across India and Africa the two species Gossypium herbaceum and Gossypium arboreum. Nobody was carrying seed between these regions. The pattern is the one that already holds for ceramics and for metallurgy. Communities far apart, with no contact, set out on the same trajectory of invention thousands of years ago and arrived at the same transformative technology by their own routes, working with whatever grew where they lived.