A new archaeobotanical study by researchers from the University of Oxford and Kiel University (CAU) has revealed that increases in cereal grain size at the dawn of agriculture, more than 11,000 years ago, were initially driven by plants' plastic responses to favorable growing conditions, rather than by genetic selection under cultivation as previously thought.
To test competing explanations for early grain enlargement, the international team applied an integrated analytical approach combining morphological, weed ecological and stable carbon isotope analyses of charred barley and emmer wheat remains recovered from the Pre-Pottery Neolithic settlements of el-Hemmeh and Sharara in the Wadi el-Hasa, Jordan. The study, now published in the Proceedings of the National Academy of Sciences, shows that developmental plasticity played a key role in shaping the evolutionary trajectories of cereals before they became domesticated.
Early signs of cultivation
Around 11,000 years ago, Neolithic communities across southwest Asia began producing their own food by bringing wild cereals, legumes and fruit-bearing plants under cultivation. Over the following millennia, these practices transformed hunter-gatherer lifeways and eventually gave rise to farming societies in which domesticated cereal crops were central to subsistence, storage and the accumulation of surplus.
Wild cereals naturally possess a brittle, or shattering, rachis that allows mature seeds to disperse easily, promoting successful germination in the wild but making seed harvesting by people difficult. In comparison with later domestic cereals, wild cereals also have relatively small grains. Decades of archaeobotanical research have shown that systematic cultivation of cereal crops gradually selected for larger grains and a tough rachis that keeps seeds attached to the ear after ripening, making harvesting more efficient.
Rethinking larger grains
"Crop domestication was a highly variable and protracted process that unfolded across multiple regions of southwest Asia," said Dr. Jade Whitlam (University of Oxford), who led the study. "Over the past decade, archaeobotanical research has revealed that domestication was preceded by a lengthy period of 'pre-domestication cultivation,' which is thought to have created the conditions that favored the evolution of key domestication traits."
Previous studies have interpreted larger cereal grains and the appearance of plants that would later become weeds of cultivation at Early Neolithic sites as evidence that people were already tilling soils and that selection for domestication traits was underway. Larger grains recovered from southern Levantine sites have therefore often been viewed as among the earliest indicators of domestication.
"At el-Hemmeh and Sharara, both barley and emmer wheat remained morphologically wild in the initial phases of the Pre-Pottery Neolithic, with no evidence of domesticated nonshattering forms," Whitlam said. "Yet grain size varied dramatically, ranging from typically wild-sized grains to grains that were comparable in size to domesticated cereals. At the same time, ecological analysis of weedy plant taxa associated with these cereals indicates they were growing in low-disturbance environments, challenging the idea that larger grains were selected for through cultivation practices such as systematic tillage."
To investigate what was driving these differences, the team carried out stable carbon isotope analysis on the charred cereal grains. The stable carbon isotopic composition of cereal grains is strongly influenced by the moisture available to plants as they grow, allowing the team to infer their growing conditions.
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A team member wades through water in the mountainous terrain of Wadi el-Hasa, where people first experimented with agriculture 11,000 years ago. Credit: Jerome Poulalier -
Professor Cheryl Makarewicz, senior author of the study, investigating a early neolithic domestic structure at Sharara. Credit: Bill Finlayson
Water shaped grain size
"Interestingly, the barley grains that fall within the size range of domestic-sized grains show carbon isotope values indicating they grew under wetter conditions," said Dr. Pascal Flohr (University of Kiel and the University of Oxford), who has carried out extensive field-based experimental work in Jordan establishing the relationship between water stress and the carbon isotopic composition of cereals. "In contrast, the smaller wild-sized grains have isotope values that indicate they grew under much drier conditions, revealing that water availability had a major influence on grain size."
"Once we integrated the archaeobotanical, weed ecological and isotopic evidence, it became clear that environmental conditions provided a much better explanation for the observed variation in grain size than genetic selection under tillage," Whitlam said. "Our findings show that developmental plasticity rather than genetic change accounts for initial increases in cereal grain size in the Early Holocene southern Levant. This suggests that genetic selection for larger grain size may have occurred later than previously thought, perhaps only after selection for the nonshattering rachis."
"This study demonstrates the value of bringing together long-term archaeological field projects with new analytical approaches. By integrating evidence from archaeobotany, stable isotopes and plant ecology, we can ask entirely new questions about how the transition to agriculture unfolded. Taken together, these findings suggest that Early Neolithic plant management practices appear to have been part of the long history of hunter-gatherer niche construction rather than a radical new intention to domesticate," said Professor Cheryl Makarewicz, senior author of the study and director of the excavations at el-Hemmeh and Sharara, the latter with her colleague Dr. Bill Finlayson (Oxford), also a co-author on this research.
Publication details
Jade Whitlam et al, Developmental plasticity under human management shaped cereal evolution prior to domestication in the Early Holocene southern Levant, Proceedings of the National Academy of Sciences (2026). DOI: 10.1073/pnas.2535274123
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Citation: Early farmers' larger grains may reflect rainfall, not genetic selection (2026, August 11) retrieved 12 August 2026 from https://phys.org/news/2026-08-early-farmers-larger-grains-rainfall.html
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