PEOPLE FOR THE EARTH 581 



health, resulted in a steady lengthening of human life during the 

 latter part of the nineteenth century and the early part of the 

 twentieth. The average length of Ufe in parts of Europe and in 

 parts of this country has been increased by as much as from ten 

 to over twenty years. In India, where the people refused to 

 adopt modern ideas and modern methods, there was no improve- 

 ment whatever. There the average length of life has remained 

 at about twenty-four years, whereas in the other countries it has 

 gone up to fifty years or more. Where disease kills a large num- 

 ber of people, those who survive are probably less susceptible, 

 or more resistant, to the particular infections, and we should 

 expect that through natural selection the race would in time 

 come to be immune. We have already seen that, whereas light- 

 skinned races are more immune to some diseases (measles and 

 tuberculosis), the dark-skinned are more immune to others 

 (hookworm disease and malaria). 



By saving lives, or postponing deaths, civilization interferes 

 with natural selection. Many people have feared that for this 

 reason civilization must lead to a complete degeneration of the 

 race, until we become quite unfit to live. It is a real danger, for 

 example, if several generations of people have been shielded 

 from infection by measles and the disease is then introduced. 

 There is likely then to be a very high proportion of deaths. 

 While there is a real danger, two things ought to be remembered 

 in this connection : 



1. If we can guard against measles or smallpox infection for 

 a few generations, we ought to be able to keep up the protection 

 indefinitely, and even in time exterminate the disease. 



2. There is no connection whatever between the fitness to 

 resist a particular infection and other kinds of fitness that have 

 human value. 



Many of the greatest men and women who have ever lived were not 

 perfect organisms in the sense of having perfect health. John Milton 

 was blind ; Beethoven and Thomas A. Edison became deaf ; Robert 

 Louis Stevenson and Keats were consumptives. There have been great 

 writers and artists who were lame or humpbacked. The reason why our 



