Page - 178 - in The Origin of 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 perfec- tion—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 Con- ditions of Existence embraced by the theory of Natural Selection. LONG before the reader has arrived at this part of my work, a crow^d 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 stag- gered; but, to the best of my judgment, the greater number are only apparent, and those that are real are not, I think, fatal to theory. r These difficulties and objections may be classed under the \ following heads;—First, why, if species have descended from V" other species by fine gradations, do we not everywhere see 's innumerable transitional forms? Why is not all nature in }$ confusion, instead of the species being, as we see them, well I defined? L- 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 produce, on the one hand, an organ of trifling impor- tance, such as the tail of a girafife, 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 178