Discussions and conclusions
Genetic tests that are sufficiently comprehensive and specifically planned to throw light on the mode of origin of the Southwest Asian founder crops have not yet been attempted. The genetic eveidence cited in this chapter consists mainly of facts extracted from experiments designed to answer totally different questions. Inevitably, these are just fragments of information, frequently in need of further confirmation and additional support from intentionally designed tests. In spite of these limitations, the available evidence leads to the following conclusions:
The mode of domestication of the Southwest Asian founder crops (as well as other cultivated plants) need not remain an open question. Several kinds of genetic tests can be proposed for obtaining critical evidence. If carried out on a sufficient scale, such examinations could provide firm evidence for discriminating between monophyletic and polyphyletic origins.
Some of the available genetic evidence (such as chromosome polymorphism in lentil, chloroplast DNA polymorphism in barley, sibling species in tetraploid wheats, the nature of the loss of wild-type seed dispersal and germination inhibition) already appear to be highly indicative. Taken together with the floristic information on species composition, they suggest that at least emmer wheat the most important crop of Southwestern Asian and European Neolithic agriculture as well as pea and lentil (the main legumes) were each taken into cultivation only once, or at most only very few times. Evidence pertaining to the mode of origin of einkorn wheat, chickpea, bitter vetch and flax is much more meager, yet the data seem to be compatible with the notion of a single origin in each case. Only barley, where two different non-shattering genes (bt and bt) have been discovered (Takahashi 1964), is there an indication that this important crop has been taken into cultivation more than once. Yet even here the chloroplast DNA data suggest that only very few events have occurred.
In conclusion, the available data fragmentary as they are appear to support the hypothesis that the development of grain agriculture in Southwest Asia was triggered (in each crop) by a single domestication event or at most by very few such events. However, although such mode of origin is indicated for the majority of the founder crops, the data tell us very little about the way the Southwest Asian Neolithic crop package was assembled. It remains an open question whether these crops were taken into cultivation together in the same place, or whether different crops were domesticated (perhaps each only once) in different places. Yet once the technology of crop cultivation was invented, and the domesticated forms of wheats, barley, pulses and flax first appeared, they probably spread over the Near Eastern arc in a manner similar to the way in which they later spread into Europe: not by additional domestications in each species but by diffusion of the already existing domesticates. In other words, soon after the first non-shatttering and easily germination cereals, pulses and flax appeared, their superior performance under cultivation became decisive and there was no need for repeated domestication of the wild progenitors. Moreover, because this new system of crop cultivation expanded rapidly, there was little chance for grain agriculture to develop independently elsewhere in Southwest Asia or Europe. This is apparently true not only for the Neolithic founder crops but also for the first Southwest Asian domesticated herd animals: sheep and goat (cf. Uerpmann, Legge and Hole in Chs 12,13 and 14 in this volume).
From Origins and Spread of Agriculture and Pastoralism in Eurasia edited by David Harris