Unearthing the origins of agriculture

Unearthing the origins of agriculture

John Carey writes:

Archaeobiology involves gathering and analyzing the remains of humans and plants to discern how people were living and what they were eating and doing. It started first with bioarchaeology, a term coined in the 1970s for the study of human bones and teeth, explains Clark Larsen, an anthropologist at The Ohio State University in Columbus. Researchers can use clues in bone structure and advanced technologies to determine whether our ancestors walked or ran a lot, measure isotopes of elements such as carbon and nitrogen to gauge past diets, read ancient human DNA to chart the movements of people and populations, and spot the telltale genes of pathogens such as tuberculosis and leprosy in human remains.

For plant material, collected using a super-fine mesh to strain out tiny bits of char or seeds, genetic technologies make it possible to read not just entire genomes but also to determine which genes are turned on or off over the years, as the relationship between plants and humans gradually evolves, as shown by the related field of archaeobotany. “The amount of information we can obtain at the genomics and transcriptomics levels about plant domestication is absolutely mind-blowing,” says [geneticist Hugo] Oliveira [at the Universidade do Algarve in Faro, Portugal].

These technologies have helped detail not only agriculture’s origins but also the intricate patterns of proliferation. The starting point goes all the way back to hunter–gatherers’ vast knowledge and use of wild plants. In scanning electron microscope images, charred food remains collected from fireplaces at Shubayqa 1, a site in northeastern Jordan, show the characteristic porous structure of bread—proof that people were baking loaves from wild einkorn wheat and other plants more than 14,500 years ago, long before the first actual cultivation.

Then, after the unsettled and cooler climate of the Younger Dryas, the archaeobotanical records show that wild plants began to change in two remarkable ways once the climate became warmer and more stable—conclusive evidence for domestication and then cultivation. Whether wheat and barley in the Near East starting 11,700 years ago, or rice in China more than 8,000 years ago, the plants’ seeds grew larger over hundreds and thousands of years. In addition, researchers have shown that, over long periods of time, more of the plant spikes had husks and seeds attached. Wild plants, of course, shed their seeds willy-nilly when ripe, forcing human gatherers to painstakingly pick them up from the ground. But as cultivation developed, the plants held onto their seeds longer—a phenomenon called non-shattering, which makes it easier for people to harvest the grain.

Both traits are believed to be unintended consequences of plant domestication. Some individual wild plants will have slightly larger seeds than others, so they will germinate and grow faster, shading out their competition. People are then more likely to collect the seeds from those plants. When humans began to save some grains to plant, fatter seeds would lead to bigger plants, increasing the payoff. Over centuries and millennia, the grains thus grow bigger and bigger, offering humans more caloric bang for the investments they make in sowing and cultivation. “That pulls people into more cultivation because the yields are getting better and better,” explains Fuller. At the same time, characteristics like non-shattering lead people to develop new harvest technologies like knives and sickles. [Continue reading…]

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