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
The Origins and Spread of Agriculture and Pasturalism in
Eurasia edited by David Harris
