Agriculture Reference
In-Depth Information
WHEAT DOMESTICATION AND
HUMAN CIVILIZATION
many of the evolutionary changes that resulted in
domestication. Research has enabled us to assess
the relative importance of the evolutionary forces
driving wheat evolution—hybridization, migra-
tion, drift, and natural selection—interacting in
generating the contemporary wheat genotype.
Studies suggested that, besides polyploid hybrid-
ization, natural selection played a large role and
oriented wheat evolution primarily through the
mechanisms of diversifying and balancing selec-
tion regimes (Nevo et al., 2002).
Wheat has become the world's largest and most
important food crop for direct human consump-
tion, with an annual harvest of more than 620
million tonnes produced in over 40 countries for
more than 35% of the global population
(Williams 1993). The US produces approximately
55 to 60 million tonnes per year and supplies
about 40% of the world's exports. Wheat is cur-
rently grown from 67ºN, in Norway, Finland, and
Russia, to 45ºS, in Argentina and Chile. The
world's main wheat-producing regions are in
temperate and southern Russia, the central plains
of the US, southern Canada, the Mediterranean
Basin, northern China, India, Argentina, and
Australia. Wheat makes up 29%-30% of the
world's total cereal production and is humans'
most important source of protein. As a crop for
direct human consumption, only rice comes close
to matching wheat production. As a food grain,
wheat is the major dietary component throughout
the world; in 1996 it served as the source of over
55% of the world's carbohydrates (http://www.
fao.org).
Wheat cultivars are superior to most other
cereals in their nutritive value (Zohary and Hopf
2000). Besides the grain containing from 60% to
80% starch, it also contains from 7% to 22%
storage protein, which in elite wild genotypes can
reach as much as 17% to 28% (Avivi 1978, 1979;
Avivi et al., 1983; Grama et al., 1983; Nevo et al.,
1986; Levy and Feldman 1987). The gluten
proteins in the seed endosperm impart unique
bread-baking qualities to wheat dough, which has
made wheat the staple food in the ancient and
modern world for billions of people. Only minor
amounts of wheat are occasionally used as animal
feed, with the amount being highly dependent
The earliest signs of crop domestication appeared
10,000-12,000 years ago in the Fertile Crescent
of the Near East, in Central America, and in
southern China, involving different crops and
independent cradles of domestication. Cereal
domestication was founded, in the Fertile Cres-
cent of the Near East, on crop reliability, yield,
and suitability for storage. Recent botanical,
genetic, and archaeological evidence has pointed
to a small core area within the Fertile Crescent—
near the upper reaches of the Tigris and Euphra-
tes rivers, in present-day southeastern Turkey-
northern Syria—as the cradle of cereal agriculture
(Lev-Yadun et al., 2000). Further evidence is
needed to clarify when and where wheat domes-
tication and agriculture, as driving forces of
modern civilization, originated. Was it spread in
time or space, or both, in the Fertile Crescent?
The genetic changes required for wheat domes-
tication to occur were relatively straightforward
and rapid, including selection for nonshattering,
free-threshing, nonbrittle rachis and hull-less
spike characteristics and for higher yield. In all
cereals, the gene complexes for ease of harvest,
yield, and suitability for short- and long-term
storage have been critical for domestication. The
domestication of cereals was essential for human
populations' change to an agriculture-based
society. Evolution of any crop species from
their wild progenitors to full domestication, and
the emergence of agricultural ecologies from pre-
agricultural ones, clearly established human
movement from hunter-gatherer societies to
sedentariness, urbanization, culture, and an
unprecedented population explosion (Harlan
1975, p. 295).
Considerable progress has been achieved in
characterizing the wild ancestry of Old World
crops, including cereals. The wild progenitors of
most of our cultivated plants have been satisfac-
torily identifi ed by comparative morphology and
genetic analysis. The distribution and ecological
ranges of wild relatives have also been established.
Furthermore, comparisons between wild types
and their cultivated counterparts have revealed
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