1. "For a species increases or decreases in numbers, widens or contracts its habitat, migrates or remains stationary, continues an old mode of life or falls into a new one, under the combined influence of its intrinsic nature and the environing actions, inorganic and organic.

"Beginning with the extrinsic factors, we see that from the outset several kinds of them are variously operative. They need but barely ennumerating. We have climate, hot, cold, or temperate, moist or dry, constant or variable. We have surface, much or little of which is available, and the available part of which is fertile in greater or less degree; and we have configuration of surface, as uniform or multiform.... On these sets of conditions, inorganic and organic, characterizing the environment, primarily depends the possibility of social evolution."—Spencer, "Principles of Sociology," vol. 1, p. 10.

2. "These considerations clearly prove that of the two primary causes of civilization, the fertility of the soil is the one which in the ancient world exercised most influence. But in European civilization, the other great cause, that is to say, climate, has been the most powerful.

"Owing to circumstances which I shall presently state, the only progress which is really effective depends, not upon the bounty of nature, but upon the energy of man. Therefore it is, that the civilization of Europe, which, in its earliest stage, was governed by climate, has shown a capacity of development unknown to those civilizations which were originated by soil."—Buckle, "History of Civilization," vol. 1, p. 36—37.*