CONCLUDING REMARKS. 433 



these two requisites generally concur. Under nature, 

 they do not, — even according to Darwin's showing. 

 Selection is present, there; but, by the very terms 

 of Darwin's argument, the other requisite — viz., favor- 

 able conditions, — must be absent, in order to effect 

 the Natural Selection. According to the very terms 

 of his argument, if this requisite of advance in de- 

 velopment — favorable conditions — were present, the 

 other requisite — Natural Selection — would necessarily 

 be wanting; for unfavorable conditions are required 

 (according to Darwin) to work off the weakest and 

 most degenerate, and thus occasion the Selection of 

 the others. 



Subject to this qualification, the principle of Natural 

 Selection has been recognized. The argument from 

 Natural Selection, however, is a different matter. 



10. Darwin's next proposition, is that those slight 

 variations which are assumed to arise occasionally, 

 under nature, " in the course of thousands of genera- 

 tions;" and those slight increments of development 

 which are assumed to be the outcome of the Natural 

 Selection of " the strongest and most vigorous " of each 

 generation, may be accumulated by Natural Selection 

 to an indefinite or unlimited extent : in other words, 

 that by means of the accumulation of such occasional 

 variations and of those slight increments of develop- 

 ment, the higher animals have all been evolved from 

 the lowest forms of life. 



Exception has been taken to. this proposition for the 

 same reasons which were urged against the assump- 

 tion of unlimited variation, when it was considered 

 37* 



