ORIGIN OF SPECIES 147 



petition/ Such a process may or may not lead to 

 greater complexity, but would be an evolutionary 

 change in any case. It should not ])e overlooked 

 that only a limited number of living things are rela- 

 tively complicated structures. An immense world of 

 apparently simple organisms exists on the earth at 

 the present time. Evolution has not meant the sub- 

 stitution of the simpler by the more comj^lex; both 

 exist side by side today, each standing in a different 

 relation to the environment, but neither more capa- 

 ble of remaining in existence than the other. 



The phrase natiu'al selection, or its equivalent, 

 the survival of the fittest, is generally understood to 

 mean that a new type that appears, being better 

 adapted to the same environment, displaces the old 

 type by competition. One new "species" replaces its 

 parent species. Something new has evolved, and by 

 implication something "better," i.e., something with 

 better chances of survival than the original species. 

 While such replacement of an old type by a new one 

 through competition may be one of the ways that 

 new types evolve, it would be erroneous to suppose 

 that Darwin limited the term in this wav. It would 

 be unfortunate to identify selection with such an 



1 The situation is essentially the same if the new type is fitted to 

 establish a new relation with a different part of the same original 

 environment — as when birds developed wings to take advantage of the 

 air. Such a change may, it is true, lead through competition to a 

 substitution of the new for the old type, but at other times it may 

 also remove the new from competition with the old type. Birds for 

 example have not replaced lizards. 



