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 
