exotic rivers

THERE IS A WRITTEN record on the land in the Near East. Here, civilization arose out of the mysteries of the stone age and gave rise to cultures that moved eastward to CHINA and westward through Europe and across the ATLANTIC OCEAN to the Americas. Achievements of ancient origin serve as constant reminders of our debt to the Sumerian peoples of Mesopotamia whenever we use the wheel, look at the clock or our watches to tell time divided into units of 60, or view our calendars as a revision of the method the ancient Egyptians used in dividing the year. Our inheritance in both experience and knowledge from the past is far more than we know or realize.

No one knows exactly when humans began the transition from hunting and gathering to sedentary living. But we do find a very close relationship between the organization of humans in settled areas and the rise of agriculture and the domestication of crops. Agriculture had its most referenced beginnings at least 7,000 years ago in two great centers: one in the fertile alluvial plains of a land called Mesopotamia and the other along the lower reaches of the Valley of the Nile. We shall leave the interesting question of the precise area in which agriculture originated to the archaeologists. It is enough for us to know that it was in these alluvial plains in an arid climate that the first tillers of soil began to grow food crops using IRRIGATION in quantities that exceeded their own needs.

Where agriculture was practiced under especially favorable conditions, it was even possible to produce more food than the local inhabitants actually needed at any given time. The significance of being able to produce surplus food can scarcely be overemphasized, for by releasing some workers from the day-to-day chores of tilling the fields, it permitted a diversification and specialization of labor that had never before been possible.

Of course, the basic need behind all of this is water, for without water there is little evidence of life let alone society or civilization. Even today, we find more than 90 percent of the world's population living within 62 mi (100 km) of the coast or a major navigable river. It should also be pointed out that in the wake of surplus food production and the concomitant necessity for food storage, other modifications in the material culture of the peoples were almost inevitable hallmarks of such an advance. Vessels for storage, such as baskets and pottery, now became part of the inventory of the average household. And the latter, in particular because of its relative imperishability, has become a favored diagnostic tool of the archaeologist in tracing the economic evolution of a culture.

Although examples of preagricultural ceramics do exist, the more usual case is that they are evidence of a settled, farming society of greater complexity and sophistication. It was this organization of community (or place) around a multitude of functions that led Greek scholars to later conclude that cities grew up as a response to human NEEDS AND WANTS.

RIVER CIVILIZATIONS

Historically, the archaeological evidence suggests that the first great civilizations were all river civilizations. Even more interesting is the fact that in each of these early cases, the lands on which these early civilizations took form were also very dry, DESERT or semidesert environments. Desert regions can be found on all continents and they occur in two zones, one on either side of the equator. One zone is found between 15 degrees N and 30 degrees N latitude and the other between 15 degrees S and 30 degrees S latitude. Most deserts are found on the western side of continents and extend inland. Only the Sahara Desert extends from one side of a continent to the other.

Though little rain falls in deserts, deserts receive runoff from ephemeral, or short-lived, streams fed by rain and snow from adjacent highlands. These streams fill the channel with a slurry of mud and commonly transport considerable quantities of sediment for a day or two. Although most deserts are in basins with closed, or interior, drainage, rivers that derive their water from outside the desert cross a few deserts.

These rivers receive a lot of rainfall (or snowfall) in the areas where they arise, that is, in the area known as their headwaters. This large supply of water allows them to flow across the desert even though a lot of water is lost through evaporation into the atmosphere or through seepage beneath the desert surface. These rivers are called exotic rivers because the water they carry comes from outside the desert region they pass through. Such rivers infiltrate soils and evaporate large amounts of water on their journeys through the deserts, but their volumes are such that they maintain their continuity.

These older, specially favored areas of human habitation and food production have typically been found in the so-called exotic river valleys of the Near East, such as the Tigris and Euphrates in Mesopotamia (present day IRAQ), as early as 4500 B.C.E.; in the Nile Valley of EGYPT by 4000 B.C.E.; the Indus Valley of PAKISTAN by 3500 B.C.E.; the valleys of the AMU DARYA and Syr Darya in Central Asia by 3000 B.C.E.; and the HUANG (Yellow) and Wei river valleys of North CHINA by 2500 B.C.E. In every instance there was a desert climate with cloudless skies, lots of daily sunshine, little if any frost, little or no vegetation cover to clear, and rich alluvial soils coincided with a continuous supply of water from the adjacent river. Indeed, each of these exotic river valleys was either the cradle of a civilization in its own right or, at least, the beneficiary of a diffusion, which first began in Mesopotamia and was later emulated elsewhere under remarkably similar environmental conditions.

These so-called exotic rivers cross all of the large deserts of the world, except those of AUSTRALIA. Also, desert soils are usually quite productive when supplied with water. The most widely cultivated areas are where there are water-transported soils in the form of FLOODPLAINS and ALLUVIAL FANS.

There is good evidence that in the New World the model of “hydraulic” civilizations based on exotic rivers as described above may have been first replicated in the Atacama Desert along the west coast of PERU where about 40 short exotic rivers cut their way from the ANDES to the PACIFIC OCEAN. The other New World area where a hydraulic culture occurred was in the Colorado Plateau region of the southwestern part of the UNITED STATES (the southwest Anasazi culture), where the Colorado River cuts its way from the ROCKY MOUNTAINS across the plateau and into the Sonoran and the Mojave Desert before emptying into the Gulf of California. There are a number of examples of exotic rivers where civilization did not seem to take hold. These include the Snake River in IDAHO and parts of the Columbia River which cuts through desert landscapes of WASHINGTON and OREGON. There are no exotic rivers in Europe or Australia.