Chap. VI.] DIFFICULTIES OF THE THEORY. 133 



CHAPTEE VI. 



Difficulties of the Theory. 



Difficulties of the theory of descent with modification — Absence or rarity 

 of transitional varieties — Transitions in habits of life — Diversified 

 habits in the same specks — Species with habits widely different 

 from those of their allies — Organs of extreme perfection — Modes 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 the reader has arrived at this part of my work, a crowd 

 of difficulties will have occurred to him. Some of them are so 

 serious that to this day I can hardly reflect on them without being 

 in some degree staggered ; but, to the best of my judgment, tht 

 greater number are only apparent, and those that are real are not, 

 I think, fatal to the theory. 



These difficulties and objections may be classed under the follow- 

 ing heads : — First, why, if species have descended from other species 

 by fine gradations, do we not everywhere see innumerable tran- 

 sitional 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 modifi- 

 cation of some other animal with widely-different habits and 

 structure? Can we believe that natural selection could produce, 

 on the one hand, an organ of trifling importance, such as the tail of 

 a giraffe, which serves as a fly-flapper, and, on the other hand, an 

 organ so wonderful as the eye ? 



Thirdly, can instincts be acquired and modified through natural 

 selection ? What shall we say to the instinct which leads the bee 

 to make cells, and which has practically anticipated the discoveries 

 of profound mathematicians ? 



Fourthly, how can we account for species, when crossed, being 

 sterile and producing sterile offspring, whereas, when varieties are 

 crossed, their fertility is unimpaired ? 



The two first heads will here be discussed ; some miscellaneous 



