WE have now, perhaps, established the truth that ease is inimical to civilization. Can we next proceed one step farther? Can we say that the stimulus towards civilization grows positively stronger in proportion as the environment grows more difficult ? Let us review the evidence in favour of this proposition and then the evidence against it, and see what inference emerges. Evidence indicating that the difficulty and the stimulus of an environment are apt to increase pari passu is not hard to lay hands upon. Rather, we are likely to be embarrassed by the wealth of illustrations that leap to the mind. Most of these illustrations present themselves in the form of comparisons. Let us begin by sorting out our illustrations into two groups in which the points of comparison relate to the physical environment and the human environment respectively; and let us first consider the physical group. It subdivides itself into two categories: comparisons between the respective stimulating effects of physical environments which present different degrees of difficulty; and comparisons between the respective stimulating effects of old ground and new ground, apart from the intrinsic nature of the terrain.
Let us, as a first example, consider the different degrees of difficulty presented by the lower valleys of the two great rivers of China. It seems that when man first took in hand the watery chaos of the lower valley of the Yellow River (Hwang Ho), the river was not navigable at any season; in the winter it was either frozen or choked with floating ice, and the melting of this ice every spring produced devastating floods which repeatedly changed the river's course by carving out new channels, while the old channels turned into jungle-covered swamps. Even to-day, when some three or four thousand years of human effort have drained the swamps and confined the river within embankments, the devastating action of the floods has not been eliminated. As recently as 1852 the channel of the Lower Hwang Ho was entirely changed and its outflow into the sea shifted from the southern to the northern side of the Shantung Peninsula, a distance of over a hundred miles. The Yangtse, on the other hand, must always have been navigable, and its floods, though they occasionally assume devastating proportions, are less