Plant sources of starch have been domesticated in several parts of the world. By the second millennium BC in various parts of Eurasia, such starchy crops are encountered, not only around their geographical regions of origin, but also at considerable distances from them. Drawing on evidence from across Eurasia, this paper explores this episode of food globalization in prehistory, comparable in the scale of its impact on global diets to the Columbian Exchange of historic times. Possible reasons for the earlier episode of food globalization are discussed and situated within a broader consideration of cross-continental contact in prehistory.

The geographic distribution of genetic diversity and the population structure of tetraploid wheat landraces in the Mediterranean basin has received relatively little attention. This is complicated by the lack of consensus concerning the taxonomy of tetraploid wheats and by unresolved questions regarding the domestication and spread of naked wheats. These knowledge gaps hinder crop diversity conservation efforts and plant breeding programmes. We investigated genetic diversity and population structure in tetraploid wheats (wild emmer, emmer, rivet and durum) using nuclear and chloroplast simple sequence repeats, functional variations and insertion site-based polymorphisms. Emmer and wild emmer constitute a genetically distinct population from durum and rivet, the latter seeming to share a common gene pool. Our population structure and genetic diversity data suggest a dynamic history of introduction and extinction of genotypes in the Mediterranean fields.

Many of today's major food crops are distributed worldwide. While much of this 'food globalisation' has resulted from modern trade networks, it has its roots in prehistory. In this paper, we examine cereal crops that moved long distances across the Old World between 5000 and 1500 BC. Drawing together recent archaeological evidence, we are now able to construct a new chronology and biogeography of prehistoric food globalisation. Here we rationalize the evidence for this process within three successive episodes: pre-5000 BC, between 5000 and 2500 BC, and between 2500 and 1500 BC. Each episode can be characterized by distinct biogeographical patterns, social drivers of the crop movements, and ecological constraints upon the crop plants. By 1500 BC, this process of food globalisation had brought together previously isolated agricultural systems, to constitute a new kind of agriculture in which the bringing together of local and exotic crops enables a new form of intensification.

Today, farmers in many regions of eastern Asia sow their barley grains in the spring and harvest them in the autumn of the same year (spring barley). However, when it was first domesticated in southwest Asia, barley was grown between the autumn and subsequent spring (winter barley), to complete their life cycles before the summer drought. The question of when the eastern barley shifted from the original winter habit to flexible growing schedules is of significance in terms of understanding its spread. This article investigates when barley cultivation dispersed from southwest Asia to regions of eastern Asia and how the eastern spring barley evolved in this context. We report 70 new radiocarbon measurements obtained directly from barley grains recovered from archaeological sites in eastern Eurasia. Our results indicate that the eastern dispersals of wheat and barley were distinct in both space and time. We infer that barley had been cultivated in a range of markedly contrasting environments by the second millennium BC. In this context, we consider the distribution of known haplotypes of a flowering-time gene in barley, Ppd-H1, and infer that the distributions of those haplotypes may reflect the early dispersal of barley. These patterns of dispersal resonate with the second and first millennia BC textual records documenting sowing and harvesting times for barley in central/eastern China.

Increase in grain/seed size recurrently features as a key element in the 'domestication syndrome' of plants (cf. Zohary and Hopf 2000; Fuller et al. 2014). In the context of its spread across Eurasia, however, the grain size of one of the world's major crop species underwent a substantial reduction. Between the fifth and second millennia BC, the grain length in a number of species of Triticum, collectively known as free-threshing wheat, decreased by around 30%. In order to understand and help account for this trend, we have obtained direct radiocarbon measurements from 51 charred wheat grains and measured the dimensions of several hundred grains from Asia to establish when and where that size diminution occurred. Our results indicate that the pace of a eastward/southward spread was interrupted around 1800 BC on the borders of the distinct culinary zone recognized by Fuller and Rowlands (2011), but regained pace around 200-300 years later in central-east China with a diminished grain size. We interpret this as evidence of a period of active crop selection to suit culinary needs, and consider whether it constitutes a distinct episode in the general character of genetic intervention in domesticated species.