124 DIFFICULTIES OF THE THEORY [CHAP. VI. 



arise from reversion and analogous variation, such modifications 

 will add to the beautiful and harmonious diversity of nature. 



Whatever the cause may be of each slight difference between 

 the offspring and their parents and a cause for each must exist 

 we have reason to believe that it is the steady accumulation of 

 beneficial differences which has given rise to all the more impor- 

 tant modifications of structure in relation to the habits of each 

 species. 



CHAPTER 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 species Species with habits widely different from those of their allies 

 Organs of extreme perfection Modes of transition Cases of difficulty 

 datura 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, 

 the 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 

 following heads: First, why, if species have descended from 

 other species by fine gradations, do we not everywhere see 

 innumerable transitional forms ? Why is not all nature in con- 

 fusion, 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 other animal with widely different habits 

 and structure ? Can we believe that natural selection could pro- 

 duce, 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 1 



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 1 



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



