312 MISCELLANEOUS OBJECTIONS TO THE [Chap. VIL 



in question. With respect to climbing plants, I need 

 not repeat what has been so lately said. 



It has often been asked, if natural selection be so 

 potent, why has not this or that structure been gained 

 by certain species, to which it would apparently have 

 been advantageous? But it is unreasonable to expect a 

 precise answer to such questions, considering our ignor- 

 ance of the past history of each species, and of the condi- 

 tions which at the present day determine its numbers 

 and range. In most cases only general reasons, but in 

 some few cases special reasons, can be assigned. Thus 

 to adapt a species to new habits of life, many co-ordi- 

 nated modifications are almost indispensable, and it may 

 often have happened that the requisite parts did not 

 vary in the right manner or to the right degree. Many 

 species must have been prevented from increasing in 

 numbers through destructive agencies, which stood in 

 no relation to certain structures, which we imagine 

 would have been gained through natural selection from 

 appearing to us advantageous to the species. In this 

 case, as the struggle for life did not depend on such 

 structures, they could not have been acquired through 

 natural selection. In many cases complex and long-en- 

 during conditions, often of a peculiar nature, are neces- 

 sary for the development of a structure; and the re- 

 quisite conditions may seldom have concurred. The 

 belief that any given structure, which we think, often 

 erroneously, would have been beneficial to a species, 

 would have been gained under all circumstances through 

 natural selection, is opposed to what we can understand 

 of its manner of action. Mr. Mivart does not deny that 

 natural selection has effected something; but he con- 

 siders it as " demonstrably insufficient " to account for 



