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Wadi el-Hasa, Jordan
Image Credit:
Kerem bm, CC BY-SA 3.0, via Wikimedia Commons
Larger Grains Did Not Necessarily Mark the Start of Farming
New archaeological research from southern Jordan suggests that larger cereal grains appeared before full domestication not because early farmers were ploughing or systematically tilling fields, but because wild plants responded to differences in water availability.
The study examined charred barley and wheat remains from the Early Holocene sites of Sharara and el-Hemmeh in the Wadi el-Hasa. These settlements preserve evidence spanning the Pre-Pottery Neolithic A, beginning in the tenth millennium BCE, and the later Pre-Pottery Neolithic B.
Cereal domestication is usually identified through traits that distinguish crops from their wild ancestors. Two of the most important are larger grains and nonshattering ears. Wild cereals naturally release their mature grains, while domesticated forms retain them until harvesting and threshing.
Because larger grains appeared in the archaeological record before nonshattering ears became common, researchers have often argued that cultivation—especially repeated tillage—selected genetically for increased grain size.
The new study challenges this interpretation.
Researchers combined measurements of ancient barley grains with analysis of cereal rachis fragments, stable carbon isotopes and the ecological characteristics of weeds found alongside the crops.
The rachis remains showed that barley and emmer wheat from the earliest occupation phases at Sharara and el-Hemmeh were still morphologically wild. Their ears continued to shatter naturally. By the later occupation at el-Hemmeh, however, both cereals displayed the nonshattering characteristics of domesticated populations.
Grain measurements produced a different pattern. Early wild barley from el-Hemmeh included grains that fell within size ranges commonly described as “domestic-sized,” while the later domesticated population did not differ greatly in average size.
This showed that grain size alone did not reliably indicate whether a cereal population was genetically domesticated.
Stable carbon isotope analysis provided a possible explanation. Within individual barley populations, larger grains generally developed under conditions of greater moisture availability, while smaller grains tended to be associated with greater water stress.
The difference represents developmental plasticity—the ability of plants with the same genetic background to develop different physical characteristics in response to environmental conditions.
The weed remains also offered no evidence that the early cereals grew in fields exposed to systematic annual tillage. Instead, the associated plants resembled those found in relatively undisturbed wild cereal habitats.
The findings therefore suggest that larger grains during the earliest stages of human cereal management were not genetic adaptations to deep burial caused by ploughing. They were at least partly temporary responses to favourable growing conditions.
Early communities may nevertheless have actively managed cereal stands. Possible practices included protecting plants from grazing animals, periodically resowing harvested grain and selecting stands growing in wetter locations. The isotope evidence does not, however, support intensive artificial irrigation.
The researchers propose a revised sequence for cereal domestication. Improved growing conditions first allowed some wild plants to produce larger grains through developmental plasticity. These desirable characteristics may have encouraged closer and more sustained relationships between people and cereals.
Continued harvesting and resowing then favoured plants with nonshattering ears, a genetically inherited trait that depended on long-term human intervention. Genetic selection for consistently larger grains may have followed later, after natural seed-dispersal pressures had weakened.
The study does not deny the role of genetic evolution in domestication. Instead, it suggests that environmentally produced physical changes helped shape the conditions under which later genetic selection occurred.
The results challenge the use of large grain size as automatic proof of early cultivation and demonstrate that domestication was a gradual process involving changing environments, plant flexibility and human management.
Published on: 05-08-2026
Edited by: Abdulmnam Samakie
Source: PNAS
