Early farmers' larger grains may reflect rainfall, not genetic selection

A new archaeological study has revealed that the early enlargement of cereal grains, dating back over 11,000 years, was primarily driven by plants' inherent plastic responses to favorable growing conditions rather than genetic selection during cultivation, according to researchers from the University of Oxford and Kiel University.

The study, published in the Proceedings of the National Academy of Sciences, challenges the long-held belief that larger grain sizes in cereals were a result of humans selecting for domestication traits. The researchers analyzed charred barley and emmer wheat remains from Pre-Pottery Neolithic settlements in Jordan, applying an integrated approach that included morphological, weed ecological, and stable carbon isotope analyses.

They found that developmental plasticity played a significant role in shaping cereal grain size evolution before domestication took place. While domesticated cereals have larger grains and tougher rachises that make harvesting more efficient, wild cereals possess smaller grains and a brittle rachis that allows easy seed dispersal.

The study suggests that water availability had a major influence on grain size, with larger grains growing in wetter conditions and smaller wild-sized grains thriving in drier environments. The findings indicate that genetic selection for larger grain size may have occurred later than previously thought, perhaps only after the selection for the nonshattering rachis.