THE RATE OF REPRODUCTION 131 



on the part of civilized women, the trouble and 



cost of rearing large families of children, the 



impossibility of rearing that many children wisely, 



and many other such considerations make it out of 



the question for human beings to reproduce up to 



the animal limit. Parents are not willing to make 



this much sacrifice, and it would not be wise if 



they did. 



In new countries the average rate of increase in a single 



generation is between three and four children to the family. 



In old countries it is less, going down close to two 



children for each family, or in some countries a fraction 



less than two. This means gradual "race suicide," for a 



species can not be kept going if a pair brings less than a 



pair to maturity. Eet us assume the higher number for 



the new country, or four children to each home. It is 



clear that at this rate each generation doubles the native 



population, and that if all the human beings lived, a very 



few generations would stock the earth up to its utmost 



limit of support. Some parts of the world, as the more 



populous parts of China, seem to have reached this 



condition now. 



4. The Difference between the Rate of Reproduction 

 and the Real Increase. Any one of the species of plants 

 and animals would become a pest to us if they really 

 multiplied at the high rates indicated as theoretically 

 possible. The human race itself would soon find life 

 intolerable if it reproduced to its full limit. But no species 

 ever does. The winters and the drouths, starvation and 

 internal weakness and disease, parasites and other enemies, 

 — such things sweep off countless millions of all these 

 species. It is a great struggle that goes on all the time 

 among all the animals and plants that are born; for, in the 

 long run, if a million are produced by two parents, only 

 two can come to maturity. Many students think that it 

 is out of this severe struggle that improvement has come 



