148 DARWINISM TO-DAY. 



''known facts of nutrition." The interested reader may find 

 this explanation in the appendix to this chapter. 



Doubt is expressed by some biologists of the reality and 

 fierceness of the struggle for existence which is an essential 

 part of the selection theory. De Vries ex- 



; urged P resses the belief that the intra-specific strug- 

 against the rig- gi e> that is, the struggle and competition among 



our of selection. . . 



individuals of the same species, has been much 

 overrated. And a few observations 1 have actually been 

 made which indicate that for certain species this struggle 

 is at least not rigorous enough to give to the slight Dar- 

 winian variations a determining value as to the character 

 of the surviving individuals. Here again the proof for the 

 Darwinian point of view is not one so much of observa- 

 tion although actual life-and-death combats between indi- 

 viduals of a single species, and innumerable examples of 

 the preying of one species on another are familiar as it is 

 a proof of reasoning. The fact of an over-production of 

 eggs and embryos, that is, of reproduction by multiplica- 

 tion, is undeniable. The lack of existing space and food 

 for all individuals, if all should live the ordinary span of 

 life peculiar to the species, is demonstrable by mathematics. 

 The consequent conclusion of these two established premises 

 is a struggle for existence. That is the sound Darwinian 

 position. 



The principal answer of the Darwinians to the criticisms 

 levelled at the theory of sexual selection is, that however 



ineffective the theory is to explain many of the 



Answer to the < ., . ,/ ., L 1 



objections to the phenomena it is called on to cover, it is at least 

 sexual selection so much more reasonable and satisfying as an 



theory, . . 



explanation of some of the phenomena, that is, 

 some of the categories of secondary sexual characters, such 

 as the ornamental plumes and colour-patterns of birds, the 

 sound-making organs of insects, etc., than any alternative 

 explanation that has been offered, that until a better expla- 



