THE ELEMENTS OF ORGANIC EVOLUTION. 83 



Neo-Lamarckians, " Change of function produces changes 

 of structure; it is a tenable hypothesis that changes of 

 structure so produced are inheritable." 



The transmission of acquired characters is still one 

 of the hypothetical factors of evolution, but we may 

 here give it only this passing reference. Among the 

 remaining factors which promote variety in life must be 

 reckoned variation in environment. No two organisms 

 can have exactly the same surroundings, and the sur- 

 roundings modify development. With this goes the 

 destruction of the unadapted, the various phases of the 

 great sifting process known collectively as natural 

 selection. The " survival of the fittest " must rest on 

 the existence of the fittest. The "origin of the fittest" 

 involves a series of difficult problems, some of them still 

 unsolved. 



IV. Natural Selection. The great motive power of 

 organic evolution is the force or process of natural selec- 

 tion. In the conditions of life those organisms last long- 

 est which are best fitted to these conditions. The term 

 "natural selection " originated from the use of the word 

 "selection" by breeders of animals to indicate the 

 process of " weeding out " by which they improve their 

 breeds. For the method by which in Nature a new spe- 

 cies is brought into existence seems to be precisely par- 

 allel to that by which we may artificially produce a new 

 breed of cows or of dogs, a new race of pigeons, or a 

 new variety of roses. 



Throughout all Nature the number of organisms 

 brought into life is far in excess of the number of those 

 which can come to maturity. All live that can live, 

 and in general those that can not live are those whose 

 individual variations are least favourable. Only a small 

 minority of the whole reach their full growth. The 

 destruction of the others, to use Bergen's words, is 



