which has established its leadership in the course of survival struggle.

The total body of historical evidence bearing on human experiments with
civilization is extensive and impressive. It covers a large portion of
the Earth's land surface, includes parts of Asia, Africa and Europe and
extends sketchily to the Americas. In time it covers many thousands of
years.

Experiments with civilization have been conducted in highly selective
surroundings possessing the volume and range of natural resources and
the isolation and remoteness necessary to build and maintain a high
level of culture over substantial periods of time. In these special
areas it was possible to provide for subsistence, produce an economic
surplus large enough to permit experimentation and ensure protection
against human and other predators. Egypt and the Fertile Crescent were
surrounded by deserts and high mountains. Crete was an island, extensive
but isolated. Productive river valleys like the Yang-tse, the Ganges and
the Mekong have afforded natural bases for experiments with
civilization. Similar opportunities have been provided by strategic
locations near bodies of water, mineral deposits and the intersections
of trade-routes. Others, less permanent, were located in the high Andes,
on the Mexican Plateau, in the Central American jungles.

Histories of civilizations, some of them ancient or classical, have
been written during the past two centuries. There have been general
histories in many languages. There have been scholarly reports on
particular civilizations. Prof. A.J. Toynbee's massive ten volume _Study
of History_ is a good example. Still more extensive is the thirty volume
history of civilization under the general editorship of C.K. Ogden.
These writings have brought together many facts bearing chiefly on the