The effect of geographical margins on cereal grain size variation: Case study for highlands of Kyrgyzstan

Archaeobotanical research in prehistoric Central Asia and beyond has repeatedly reported highly compact wheat and barley varieties found along piedmont sites of the Inner Asian Mountain Corridor (IAMC). The morphotypical variation of wheat caryopses across Eurasia generated the Liu et al. (2016) publication pointing out a decrease in grain size relative to eastward dispersal into China; the decrease in wheat caryopses was explained as human selection of smaller grain sizes for better culinary properties.



In this study we discuss the possible effect of geographical margin, mountains in particular, on grain morphotypes. By understanding the patterns and reasoning of crop morphotypical variation in mountain zones we can better understand their subsequent dispersal patterns into lower altitudes. Here we present both wheat and barley grain measurements from four Bronze Age sites in Kyrgyzstan, located in the central Tian Shan mountains of average elevation 2000 masl. The data reveals that sites located in mountain valleys at higher elevations display a higher variability in crop dimensions. By analysing grain size variation within and between the sites in Kyrgyzstan and comparing our dataset with published metadata by Liu et al. (2016), we argue that variation in grain size was driven by environmental factors, while compact grain forms in particular could have formed in geographical margins such as mountains.