I A CHAPTER IN DARWINISM 13 



ing greatly in appearance from the cattle with which 

 the breeder started. 



Now we know of no facts which forbid us to sup- 

 pose that could a breeder continue his operations 

 indefinitely for any length of time — say for a few 

 million years — he could convert the short -horned 

 breed into a hornless breed ; that he could go on and 

 thicken the tail, could shorten the legs, get rid of the 

 hind limbs altogether by a series of insensible grada- 

 tions, and convert the race into forms like the Sirenia, 

 or sea-cows. But if he could do this, you have only 

 to give him a longer time still and there is no obstacle 

 remaining to the conversion, by the same kind of 

 process, of a polyp into a worm, or of a worm into a 

 fish, or even of a monkey into a man.^ 



So far we have supposed the interference of a 

 breeder who selects and determines the varieties which 

 shall propagate themselves ; so far we have not got a 

 complete explanation, for we must find a substitute in 

 nature for the human selection exercised by the 

 breeder. The question arises, then, ''Is there any 

 necessary selective process in nature which could have 

 operated through untold ages, and so have represented 

 the selective action of the breeder, during an immense 

 period of time ? " Strangely enough, Mr. Darwin was 

 led to the discovery of such a cause existing necessarily 

 in the mechanical arrangements of nature, by reading 

 the celebrated book of an English clergyman, the Eev. 

 Mr. Malthus, On Population. On happening to read 

 this book, Mr. Darwin himself tells us that the idea 



1 See Note B. 



