Sauer - 1993 - Historical geography of crop plants, a select rost

208 Historical Geography of Crop Plants: A Select Roster
simple textbook definitions, the three would be considered a single species.
They are in effect fairly discrete gene pools because hybrids are at a disadvantage
in both natural habitats and rice fields. (The situation is somewhat
comparable to that of the wolf and dog.)
Most of the multitude of landraces of O. sativa are evidently descended
primarily from O. nivara. The most important and evidently the most ancient
of these are the paddy or wet rice races. The so-called dry rices or hill rices
have various characteristics suggesting derivation from paddy rice. They can
be grown without irrigation in a sufficiently rainy climate. These are very
widespread in tropical shifting cultivation; they are relatively low yielding. The
so-called floating rices, grown where water levels fluctuate widely, have more
O. rufipogon genes.
O. nivara and O. rufipogon have enormous, largely overlapping ranges
extending from the Indus Valley eastward across all of Southeast Asia to
southern China and southward to Ceylon, the Bast Indies, including the Philippines
and New Guinea, and tropical Australia. This huge region was the
homeland not only of rice but also of other ancient tropical crop plants and
domestic animals, including water buffalo, intimately linked to rice cultivatión
for thousands of years. Unfortunately in this region, the available archaeological
record of dated and identified crop remains is exceedingly poor. Impressions
of rice glumes have been reported on pottery from Thailand dated at 3500
B.C. and from India dated before 2500 B.C., but there is no reason to believe
this documents cultivation. There is evidence from New Guinea of swamp
agriculture beginning at about 7000 B.C., but it is not known whether rice was
among the crops planted. For all that is known, rice may have been taken into
cultivation repeatedly at widely separated times and places in Southeast Asia
and the East Indies.
The earliest coherent archaeological evidence on early rice cultivation is
from outside the range of its wild ancestors. This was in eastern China north
of the Yangtze River. Domesticated rice has been found in various Neolithic
sites in this region dated from about 5000 B.C, until after 3000 B.C, Previously,
Neolithic cultures had developed in semi-arid regions of central China, perhaps
with Setaria and Panicum millets as their earliest grain crops. As these cultures
expanded into warmer and wetter regions, they probably acquired rice as a crop
from neighbors to the south.
After more than 2000 years of cultivation in temperate China, О. sativa was
introduced to Japan about 300 B.C. The artificial aquatic ecosystem of the
paddies helped the expansion out of the tropics, but even so, long evolution
under human and natural selection was probably required.
At the other end of the range of the wild progenitor, in northwestern India
and modern Pakistan, archaeological evidence suggests that rice was cultivated
only after the arrival of a complex of other crops introduced from the west.
These included wheat and barley, known to have been domesticated thousands
of years earlier in the Near East, and grain sorghum and other crops native
to Africa. The highly advanced Harappan civilization of the Indus Valley