By Jan Steffen
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.
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