8 WHAT IS EiJGENICS? 



and if both of these offspring grew up and in time also 

 reproduced their kind in like manner, numbers would be 

 kept just even. As a rule, however, every animal has 

 more than two offspring, generally many more. And 

 when, in the past, numbers have not been increasing, all 

 the offspring over two must on the average have been got 

 rid of before pairing, somehow or other. How has this 

 been brought about ? 



This keeping down of numbers has been the result of 

 what has been called ''the struggle for existence. '^ This 

 is not a very good name ; for the killing off of animals in 

 fights with other animals has not been the most important 

 way in which their numbers have been held in check. 

 Many more have died as the result of accident, disease, 

 and want of food. Some have failed to get a mate, and 

 have consequently left no progeny behind them. The 

 result of these innumerable deaths and failures has been 

 that the numbers of the different races of animals have 

 been kept from altering greatly. Now, some of these 

 animals were slightly superior to their fellows in some 

 way which gave them an advantage in this so-called 

 struggle for existence. It was these slightly superior 

 animals who had the best chance of survival and of repro- 

 ducing their kind, and who most often did so. They were 

 picked out by what has been called ' ' natural selection. ' * 



Life has existed on this earth for perhaps a thousand 

 million years. During all this time the best or the fittest 

 animals have been selected, as it were, in this way for 

 breeding purposes. We have seen how our savage ances- 

 tors, without always giving the matter any thought, gen- 

 erally bred from the dogs who actually succeeded best in 

 the chase. The result of this partly unpremeditated 

 selection was that in the course of a few thousand years 

 a wolf -like animal slowly changed into a dog something 

 like our greyhound. The survival of the beings best fitted 

 to their surroundings during an unthinkably long period 

 of time has led in a somewhat similar manner to some 

 lowly animal gradually giving rise to man. 



