Why did such meteoric intellectual brilliancy occur in Greece? Why are such wonderful Hindu ruins located in Cambodia in Indo-China? What has a high type of culture been able to persist for a thousand years in stormy Iceland? And why do we see in China the curious anomaly of a progressive South and a conservative North? After years of search, Mr. Huntington believes that at least a partial explanation is found in natural selection arising most frequently under the stress of over-population and migration. The principle involved is so simple and obvious that it seems almost incredible that it has been so largely ignored by students of geography, history and sociology. This work is the result of his research.