square miles are barren mountains, jungles, and swamps, and vast stretches of 

 desert that can support very little life of any kind and no human life at all. 



As we know, the density of human life varies from one region to another. 

 But most of us would be astonished to learn how great the variation actually 

 is. For Australia the population a\crages a little over 2 to the square mile; 

 in Alaska it is 1 to 10 square miles; in Japan it is over 400 to one square mile. 

 In both China and India there is so much desert and mountain area that the 

 ratio of people to /o/rt/area is very misleading — something o\er 100 per square 

 mile for China and about 180 per square mile for India. Similarly, the average 

 distribution ior Egypt is about the same as that for the United States — under 

 40 per square mile. But if we consider the regions actually occupied, the 

 density of Egypt's population rises to over 1000 per square mile. 



Europe is the most densely populated continent, and Belgium the most 

 densely populated country in Europe, having 635 to the square mile, as against 

 482 for Great Britain. If we consider England and Wales separately, however, 

 the density is about 650. This comparison suggests many questions about the 

 distribution of human life in general and about the concentration of life in 

 particular regions. 



The earliest concentrations of human population were along the shores and 

 rivers, then in fertile regions that supplied game as well as fish, and eventually 

 on soil suitable for grazing cattle and for raising crops. Cities became possible 

 only when division of labor had gone far enough. For it takes trade and traffic 

 to bring together from over a \\'ide area the needed food and raw materials 

 that city dwellers cannot produce themselves. The large industrial centers, 

 which in modern times have become the most highly crowded areas, could not 

 support life abundantly except through extensive intercourse with other 

 communities. 



Distribution Automatic If we all tried to live at the seashore, the total 

 amount of human life would be but a fraction of what it actually is. Through 

 thousands of years the human population of the earth probably increased very 

 slowlv. For aside from all other considerations, there is a limit to the number 

 of persons who can find a livelihood on the seashore or in any other specialized 

 environment. It became possible for the race to increase in numbers only as 

 it came to live in a great variety of environments. In modern times a rapid in- 

 crease in human population had to wait until we knew enough biology to con- 

 trol (1) many species of plants and animals that yield food and other useful 

 materials, and (2) those other species that interfere with our health and 

 other interests. 



The distribution, or spread, of a species away from a center is influenced 

 by the pressure of population and by the conditions in the new regions. But 

 the limiting factors always include other species, as well as the physical cop 

 ditions. 



535 



