Why did farming start?

Domestication of plants and animals arose independently in at least eleven regions of the world, and several more have been proposed. Jared Diamond’s 2002 review counted at most nine: the Fertile Crescent, China, Mesoamerica, the Andes and Amazonia, the eastern United States, the Sahel, tropical West Africa, Ethiopia and New Guinea, each domesticating its own native species.

The same review set out what determined where. The homelands were the regions where the most numerous and most valuable domesticable wild species happened to be native, and they are almost the opposite of the list of breadbaskets today. Of 148 wild herbivores and omnivores on land weighing 45 kg or more, 14 were domesticated. Of about 200,000 wild higher plants, about 100 gave a valuable domesticate.

That explains the where. It does not explain the when.

Work in the Near East has replaced the idea of a sudden transition with a long one. Management of morphologically wild plants and animals reaches back at least 11,500 years, and a long stretch of increasingly intensive management came before any change in the plants and animals that a dig can detect.

A 2011 review of that work draws the conclusion plainly: morphological change can no longer be treated as the leading edge of domestication. It also describes agriculture as arising out of broad and systematic efforts to modify local environments and biotic communities, which is management rather than accident. Plants and animals now look to have been domesticated at roughly the same time rather than fifteen centuries apart, and the same species sometimes more than once across the region.

Not everyone reads the evidence that way. Shahal Abbo, Simcha Lev-Yadun and Avi Gopher argue that most, if not all, of the Near Eastern founder crops were domesticated in one core area of south-eastern Turkey.

That pushes the beginning back and makes the turning point harder to locate, which is a better description of what the evidence shows.

The clustering in time points at climate. The last glacial was dry, low in atmospheric carbon dioxide and extremely variable on short timescales, and one hypothesis is simply that agriculture was impossible under it. After about 11,600 years ago the Holocene is warm, wet, richer in carbon dioxide and stable.

The obvious objection is the previous interglacial, which was also warm and produced no agriculture. Two answers are on offer and they are different in kind. The Antarctic ice core at Vostok shows each of the last four interglacials as a short sharp peak of warmth rather than the Holocene’s long plateau, although the same authors grant that other records suggest a stable stretch in the last interglacial as long as the Holocene. The second answer is that the people of the last interglacial were anatomically modern but behaviourally archaic, which is harder to test.

Underneath either answer the 2002 review sets four slow changes: better hunting and thinner big game, the technology to reap, roast and store wild cereals, competition between societies, and a population already growing.

No generation decided to become farmers. The 2002 review puts it that the first farmers could not have guessed the consequences and would have outlawed the first steps if they had, and that the only people in a position to choose were foragers living beside farmers, who generally looked and declined.

Monumental sites built before agriculture have shifted the argument. The early layer at Göbekli Tepe has T-shaped pillars set in circular enclosures, the two central pillars of one of them standing about 5.5 metres, and no domesticated plant or animal is known from the site, so the people who raised it were hunter-gatherers. Its excavators argue that here the social change came before farming rather than after it, and that the feasts held at such sites may have pushed people towards cultivation.

Agriculture produced storable surpluses that could feed craftspeople, kings and soldiers, and in time writing and everything built on it, including this sentence. It also produced a diet narrowed onto a few crops, and the crowd diseases, which need dense populations to persist at all and many of which came out of the herds: measles from a disease of cattle, influenza from pigs and ducks.

Whether that is a bargain anyone would take is not a question with an answer. The people who made it could not see either side of the ledger.