Multiple sources of European barley

This seems to parallel quite well with my hypothesis of a secondary expansion into Europe of the component I've labeled "West Asian", after the early Neolithic. From the paper:

The wild progenitor of barley, Hordeum spontaneum, is typically a winter-germinating species, responsive to day length (Turner et al. 2005), but recent work (H. Jones et al. 2008) has demonstrated that the non-responsive allele also occurs in wild barley in Israel, Jordan and Iran, in regions where this allele is favoured by the climatic conditions. There is strong evidence to suggest that the non-responsive allele in European cultivars (Group A) is genetically more similar to the allele in Iranian wild barleys than to the allele in wild barleys from Israel and Jordan.

and:

 Detailed genetic comparisons between groups A, B and C (H. Jones 2008; H. Jones et al. 2008) suggest that Group A represents a more recent introduction of day-length non-responsive barley into Europe, rather than the selection of non-responsiveness from within populations that diffused into Europe in the Early Neolithic. In addition, three of the nine principal groups identified on the basis of the neutral SSR markers (groups 1–3) are genetically closely related and very similar in their phenotypic characteristics. They are located in north-west and Central Europe (Figure 3b), and are made up almost entirely of  day-length non-responsive barleys (98 per cent) with a spring growth habit (98 per cent) (H. Jones et al. 2011). The distinctiveness of the landraces making up groups 1–3 suggests that the responsive/non-responsive difference between Southern and Northern Europe is not simply a reflection of current selective pressure but rather is one aspect of a more fundamental genetic difference between barley populations. These day-length non-responsive cultivars have therefore been interpreted as representing a later spread of barley into Northern Europe from the eastern part of the Fertile Crescent or beyond. This raises the issue of when they spread into Europe and whether or not they were introduced via the same route as the initial  spread of agriculture.

and:

A possible channel for the introduction of day-length non-responsive barley into Northern Europe from the east at this time could have been through early exchange networks with metal-working communities of south-eastern Europe (Sherratt 1976; Bogucki 1999: 220–21). The Chalcolithic societies of the Balkans also maintained connections further east with the west Eurasian Steppes, Anatolia, and the Caucasus in the fifth and early fourth millennia, and copper was exchanged from west to east across the steppes north of the Black Sea (Kohl 2007: 31–39). Day-length non-responsive barley could, therefore, have travelled from east to west along the same route, north of the Black Sea via the Caucasus or, perhaps more likely given its agricultural nature, south of the Black Sea through Anatolia, possibly via a coastal route around the Black Sea, and then from the Carpatho-Balkan metallurgical region into Northern Europe (Figure 3b). A similar suggestion has been made for the later appearance of the oil plant Lallemantia, which was apparently introduced into Europe in the third millennium BC, possibly along the same trade routes as tin-bronzes (Valamoti & Jones 2010). 

Antiquity Volume: 87 Number: 337 Page: 701–713

DNA evidence for multiple introductions of barley into Europe following dispersed domestications in Western Asia

G. Jones et al.

It has long been recognised that the Neolithic spread across Europe via two separate routes, one along the Mediterranean coasts, the other following the axis of the major rivers. But did these two streams have a common point of origin in south-west Asia, at least with regard to the principal plant and animals species that were involved? This study of barley DNA shows that the domesticated barley grown in Neolithic Europe falls into three separate types (groups A, B and C), each of which may have had a separate centre of origin in south-west Asia. Barley was relatively rarely cultivated by the early Linearbandkeramik farmers of Central and Northern Europe, but became more common during the fifth and fourth millennia BC. The analysis reported here indicates that a genetic variety of barley more suitable for northern growing conditions was introduced from south-west Asia at this period. It also suggests that the barley grown in south-eastern Europe at the very beginning of the Neolithic may have arrived there by different routes from two separate centres of domestication in south-west Asia. The multiple domestications that this pattern reveals imply that domestication may have been more a co-evolutionary process between plants and people than an intentional human action.

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