I AND ITS INHABITANTS 179 



civilization than has the art of agriculture. It is impossible 

 to say exactly where agriculture arose. Perhaps it developed 

 in different ways in many different regions. The great staples 

 of agriculture are the cereals — wheat, barley, rice, millet, 

 maize, rye, and oats. The majority of these are of subtropical 

 origin. Rice, however, which supports more people than any 

 other one kind of food, is probably of tropical origin. The 

 same may be true of maize. This conclusion, however, is mere 

 guesswork, for that grain has never been found in its indige- 

 nous form. Millet, which well-nigh rivals maize in the num- 

 ber of people it supports, is of great importance within the 

 tropics, but apparently it originated farther north in a sub- 

 tropical climate, such as that of Egypt. The other grains all 

 appear to have originated in regions well beyond the limits 

 of the tropics. 



Whatever may be said of the origin of agriculture, it needs 

 little demonstration to show that its effect in advancing civiliza- 

 tion has been far greater in relatively cool climates than in 

 those that are warm. It is a commonplace of history that 

 the great civilizations of early times arose in fertile plains 

 where agriculture was carried on by means of irrigation. 

 These were located more than twenty-five degrees from the 

 equator, as we see in Egypt, Mesopotamia, northern India, 

 and China. It is hard to overestimate the effect of irrigation 

 upon the early progress of civilization. Because of the neces- 

 sity of making ditches and reservoirs, and of having everything 

 ready when the water is turned on a field, the power to pre- 

 pare consciously for the distant future is enormously stimu- 

 lated. The man who depends on irrigation cannot neglect his 

 fields, for a week of carelessness may cost his whole crop. 

 He must learn, too, to live at peace with his neighbors. If 

 men who use the same stream for their water-supply quarrel 

 with one another and break down one another's dams and 

 ditches the chances are that all will suffer famine. They must 



