Chap. VI. DIFFICULTIES ON THEORY. 171 



CHAPTEE VI. 



DIFFICULTIES ON THEORY. 



Difficulties on the theory of descent with modification — Transitions — • 

 Absence or rarity of transitional varieties — Transitions in habits 

 of life — Diversified habits in the same species — Species with 

 habits widely different from those of their allies — Organs of 

 extreme perfection — Means of transition — Cases of difficulty — 

 Natura non facit saltum — Organs of small importance — Organs 

 not in all cases absolutely perfect — The law of Unity of Type 

 and of the Conditions of Existence embraced by the theory of 

 Natural Selection. 



Long before having arrived at this part of my work, a 

 crowd of difficulties will have occurred to the reader. 

 Some of them are so grave that to this day I can never 

 reflect on them without being staggered ; but, to the best 

 of my judgment, the greater number are only apparent, 

 and those that are real are not, I think, fatal to my 

 theory. 



These difficulties and objections may be classed under 

 the following heads : — Firstly, why, if species have 

 descended from other species by insensibly fine grada- 

 tions, do we not everywhere see innumerable transitional 

 forms ? Why is not all nature in confusion instead of 

 the species being, as we see them, well defined ? 



Secondly, is it possible that an animal having, for 

 instance, the structure and habits of a bat, could have 

 been formed by the modification of some animal with 

 wholly different habits ? Can we believe that natural 

 selection could produce, on the one hand, organs of 

 trifling importance, such as the tail of a giraffe, which 

 serves as a fly-flapper, and, on the other hand, organs of 



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