INFLUENCES OF ENVIRONMENT 143 



ern man lias ])resumably a hii^licr nervous organization. 

 But lliiiiliii^toii believes that since first the race gained 

 the rudiments of civilization, it has always made most 

 rapid progress under essentially the same climatic condi- 

 tions. ''The conditions are that the summers shall have 

 a sufficient degree of warmth and of rainfall to make agri- 

 culture easy and profitable, but not enough to be 

 enervating; that the winters shall be cool enough to be 

 bracing, but not deadening; and that the relation of sum- 

 mer to winter shall be such that with forethought every 

 man can support himself and his family in comfort the 

 year round, while without forethought he and his will 

 suffer seriously. " ■■"■ These conditions appear to have 

 been present in each of the great nations of history at 

 the time when it has risen to the highest degree of civili- 

 zationand power. During the early part of the Christian 

 Era there was a relatively sudden desiccation in Central 

 Asia. During the previous centuries the region was 

 moist and fertile. It supported a vast population of 

 men and animals. When the rainfall decreased fifty per 

 cent., flocks of sheep diminished and the inhabitants 

 were obliged to migrate in search of food. As these 

 nomadic tribes pressed outward from Central Asia, 

 they came in contact with others. Peoples pressed upon 

 peoples, confusion spread in every direction, the wave 

 of migration was felt in Europe two thousand miles 

 away. In Caesar's time, Europe was cold and swampy, 

 but as it became warmer the throngs of primitive peoples, 

 driven from behind by the hordes of restless nomads who 

 had forsaken the arid Caspian basin, swarmed into this 

 fertile country. Climatic changes in Rome sapi^ed the 

 strength of the original population, so that in time the 



■ "-"Ihid., pp. 381-382. 



