Across the southern savanna women decided who could marry in

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.

Sites in Haiti have produced lithic workshops given over to making large flaked-stone blades, with concentrations in the Casimira and Las Alejandrinas areas. The output is specialised. These are a standard product turned out in numbers at a place chosen for its stone, rather than general-purpose flakes struck as the need arose. Marcio Veloz Maggiolo and Jose Cruxent were among the first to document the complexes, and the size and frequency of the blades became the main indicator archaeologists use when dating preceramic sites in the region. Making blades in bulk at a quarry implies mobility, since the people using them lived elsewhere and moved between the source and the coast. It also puts Haiti near the centre of the question of how human beings first spread into the Greater Antilles, because these workshops are among the best evidence for how that expansion was supplied. Around 3000 BCE this island was producing tools for a wider region.

Crops domesticated in West Africa had taken root in southern Arabia by 3000 BCE. Once they were established in Yemen and Oman they went aboard ship, and before the third millennium was out they were growing on the Indian subcontinent. The archaeologist Dorian Fuller and his colleagues assembled the evidence: a sphere of intercontinental contact more than four thousand years old, running from Africa through southern Arabia into South Asia. The usual account of ancient long-distance trade opens with Mesopotamia and the Indus valley and gives Africa a line in the notes. Fuller's material puts African plant breeding at the head of the chain, with West African crops travelling thousands of kilometres through Arabian hands and changing what Indian farmers grew. Ehret's own summary is that historians have nearly everything still to learn here. A whole sphere of ancient exchange sat unexamined because the discipline had already settled that Africa contributed nothing to the connected world.

Southern Cushitic speakers in East Africa domesticated the cowpea by the third millennium BCE, working independently of the West African farmers who had domesticated the same plant among Niger-Congo speakers. Two centres, two cultivated varieties, two language families, one continent, and both running at the same time. The West African variety is the one that travelled. It went east with the other African exports, reached India and kept going, and it is the cowpea that turns up in cuisines far from where it started. The East African domestication stayed close to home, which is why almost nobody has heard of it, and it is the more useful of the two facts for anyone trying to understand how agricultural invention actually works. Crop improvement went on in several African regions at once, in different ecological zones, among peoples of different language families, each of them responding to the ground in front of them.