On the Origin of Species
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 -- 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, 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 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 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 be here discussed; some miscellaneous objections in the
following chapter; Instinct and Hybridism in the two succeeding chapters.
ON THE ABSENCE OR RARITY OF TRANSITIONAL VARIETIES.
As natural selection acts solely by the preservation of profitable modifications, each new
form will tend in a fully-stocked country to take the place of, and finally to exterminate,
its own less improved parent-form and other less-favoured forms with which it comes
into competition. Thus extinction and natural selection go hand in hand. Hence, if we
look at each species as descended from some unknown form, both the parent and all the
transitional varieties will generally have been exterminated by the very process of the
formation and perfection of the new form.