Environmental Engineering Reference
In-Depth Information
For centuries, rice has been the world's most important staple grain crop. This photograph
shows the mechanized harvesting and drying of sheaves on wooden supports in a i eld near
Ky¯t¯ in the early 1990s. Photograph by V. Smil.
more than 10 people/km
2
, easily 100 times as many as could be supported in the
same environments with foraging. This transition to more intensive modes of food
procurement was a matter of complex evolution, and any notion of agricultural
revolution (Childe 1951) is an indefensible intellectual construct. For example, wild
cereals were collected and processed and the resulting l our was used in baking in
Israel during the Upper Paleolithic (19,500 BCE), at least 12,000 years before the
domestication of cereals (Piperno et al. 2004). In contrast, Mexico's Tehuacán Valley
had no permanent settlements but thousands of years of crop cultivation (Bray
1977), and many settled agricultural societies retained signii cant elements of forag-
ing for millennia. Clearly, there was no orderly lock-step progression of cultivation
and sedentism, no sharp divide between foraging and incipient cultivation.
The cumulative impact of animal domestication and shifting and permanent
crop cultivation began to transform ecosystems not only on local or small regional
scales but eventually across large areas of some key biomes. As already noted,
Ruddiman (2005) has argued that humans actually took control of the climate
