Farming fed more people and gave them malaria

Between the tenth and sixth millennia BCE the new farming and herding economies changed the human relationship with disease permanently. Populations grew, and even at very low densities more people meant more transmission. People also stopped moving. Hamlets and multifamily villages appeared, and with them the rubbish tips just outside, which brought in scavengers such as rats. Food production opened further routes. Animals were penned at night inside or beside the family compound, which put herds and households in daily contact and gave pathogens somewhere to cross. Clearing land had its own effect. In early West African agriculture the cleared ground held standing water through the rainy season, and Anopheles mosquitoes bred in it. Malaria was already a major African disease thousands of years ago. Every gain in food security bought a new pathway for infection: the granary that fed a village also fed its rats, and the field that grew fonio also grew mosquitoes.

Trinidad stayed joined to the South American mainland until the Holocene, and the consequences are still visible in what lives there. Its plants and animals are continental in range, and the island holds a long list of species that never reached the rest of the Antilles. It covers about four thousand eight hundred square kilometres, which makes it the sixth largest in the chain. Most of it is low hills and badly drained lowland, with a rough northern coast as the exception. That combination of position and biological range is why archaeologists routinely call Trinidad the gateway to the Caribbean. It is worth being precise about what the label means. Anything moving out of the Orinoco country and into the island chain had to come this way, so the settlement history of every island downstream begins with what people were doing here. A Caribbean that starts in 1492 skips the door and describes only the room.

Convergence across the middle Nile shows up first in pottery, where the same styles turn up along a corridor more than a thousand kilometres long. The pots are the easy evidence. What ties the region together more firmly is ritual, and it holds along the river and far out into the surrounding country. A ceramic style can travel with a trader, an imitator, or a single potter who moves house. Ways of burying the dead, ways of marking the sacred, working assumptions about what stands between people and the divine: those spread only through intermarriage, through generations of neighbours attending each other's ceremonies, through sustained and unglamorous contact. When archaeologists identify ritual commonalities running from the Sudan belt to El-Badari, they are describing a single cultural universe rather than a trading network. The funerary practice and cosmology that later became the signature of pharaonic religion were worked out in the grasslands of the middle Nile by pastoral communities.

From 6000 BCE the peoples of the middle Nile shared far more than an economy. A body of common ideas and ritual practice took hold from south of the Nile confluence all the way north into the country where the Old Kingdom would later be founded. The people involved did not speak one language. As far north as the latitude of Aswan they spoke Eastern Sahelian tongues, a branch of Nilo-Saharan. From Aswan down to El-Badari in Middle Egypt they spoke dialects of what would become ancient Egyptian. The convergence went straight across that boundary and produced shared pottery styles, shared ceremonies and shared assumptions about the world on both sides of it. So the culture area was bilingual from the start, and the civilisation that grew out of it carried both inheritances. Egypt spoke an Afrasian language and practised a great deal that had come upriver from Nilo-Saharan speakers over three thousand years of contact.