20 ORGANIC EVOLUTION 



whether they obtained their useful character through fluc- 

 tuating variation or through mutation. This does not 

 affect the fact of their survival being determined by natu- 

 ral selection. 



Before referring to the objections to the theory of natu- 

 ral selection, let us notice a few general principles in the 

 operation of this factor in evolution. 



Observe that in the process of evolution by natural 

 selection the welfare of the individual is conserved only 

 so far as it contributes to the welfare of the race. It is 

 necessary that the more perfect individuals should survive 

 long enough to breed and hand down to their young their 

 useful qualities, but, having done this, their further life is a 

 matter of indifference, so far as the processes of evolution 

 are concerned. In case an animal or plant has several 

 breeding seasons during its normal life period, of course 

 its preservation until the completion of all these reproduc- 

 tive processes may be an important advantage to the spe- 

 cies, and, if so, will tend to be secured ; but in the case of 

 a species whose members have but a single reproductive 

 period in a lifetime, as is the case with many insects for 

 example, their persistence after the completion of the pro- 

 cesses of reproduction would be even disadvantageous to 

 the species, since they would consume food and occupy 

 space needed for the younger individuals which are to 

 continue the species by reproduction. It is natural to 

 find, then, as we do among the insects, the adults usually 

 dying after the breeding season is over. The same thing 

 is true, of course, of all annual plants. Among some kinds 

 of animals the parents care for the young after birth, and 



