THE NUMBERS OF MEN 93 



So then we are left with the first alternative, a very slow and 

 irregular time rate of growth of world population over a very 

 long time prior to the Middle Ages, let us say, followed by a 

 relatively tremendous spurt of growth not yet ended. 



The implications of the three alternative hypotheses will be 

 made plainer by the diagram shown in Figure 17. 



For reasons of practical convenience in drawing and repro- 

 duction this diagram is scaled as though the total period of 

 man's life on the earth prior to the 1 7th century was a span of 

 100,000 years instead of the 500,000 that seems undoubtedly 

 much nearer the truth. The diagram understates the case by 

 so much. 



How is this sharp spurt of population growth after 1930 to 

 be explained? The primary cause behind the new cycle of logis- 

 tic growth of world population that started in the seventeenth 

 century seems clearly to have been that mankind first became 

 aware at about that time that its effective universe was expand- 

 ing. The earth was not growing physically bigger to be surej 

 there were no new acres of land being really added to the planet. 

 But many were being discovered, uncovered, and put to use, 

 and, in general, man's effective universe for purposes of living 

 certainly was expanding j and at an accelerating rate. This was 

 being brought about by new discoveries and new ideas that 

 made it possible for man to exploit far more effectively than he 

 had known how to before, the natural resources for human 

 living inherent in the earth on which he lived. One of the most 

 important and obvious aspects of the expansive changes in man's 

 effective universe that have appeared in the last three hundred 

 years was the ever increasing facility of communication and 

 transportation, with its consequent broadening of the base and 

 acceleration of the temfo of trade. Indeed it was the develop- 

 ment of railroads that had a large part in making the gloomy 

 prophecies of Malthus about the future of mankind at the end 

 of the 18th century seem comically absurd soon after he made 

 them. Another change of similar sort was the development of 

 relatively cheap and highly effective power, associated in the 



