CHAPTER XV 



Recapitulation and Conclusion 



Recapitulation of the Objections to the Theory of Natural Selection — ^Re- 

 capitulation of the General and Special Circumstances in its Favor — 

 Causes of the General Belief in the Immutability of Species — How far 

 the Theory of Natural Selection may be extended — Effects of its Adop- 

 tion on the Study of Natural History — Concluding Remarks. 



As this whole volume is one long argument, it may be convenient 

 to the reader to have the leading facts and inferences briefly re- 

 capitulated. 



That many and serious objections may be advanced against the 

 theory of descent with modification through variation and natural 

 selection, I do not deny. I have endeavored to give to them their 

 full force. Nothing at first can appear more difficult to believe 

 than that the more complex organs and instincts have been per- 

 fected, not by means superior to, though analogous with, human 

 reason, but by the accumulation of innumerable slight variations, 

 each good for the individual possessor. Nevertheless, this diffi- 

 culty, though appearing to our imagination insuperably great, can- 

 not be considered real if we admit the following propositions, 

 namely, that all parts of the organization and instincts offer, at 

 least, individual differences — that there is a struggle for existence 

 leading to the preservation of profitable deviations of structure or 

 instinct — and, lastly, that gradations in the state of perfection 

 of each organ may have existed, each good of its kind. The truth 

 of these propositions cannot, I think, be disputed. 



It is, no doubt, extremely difficult even to conjecture by what 

 gradations many structures have been perfected, more especially 

 among broken and failing groups of organic beings, which have 

 suffered much extinction; but we see so many strange gradations 

 in nature, that we ought to be extremely cautious in saying that 

 any organ or instinct, or any whole structure, could not have ar- 

 rived at its present state by many graduated steps. There are, it 

 must be admitted, cases of special difficulty opposed to the theory 

 of natural selection: and one of the most curious of these is the 

 existence in the same community of two or three defined castes of 



413 



