the differentiation of the flower into calyx and corolla, the second
cotyledon or seed-leaf and several other characters. Losses of characters
such as these may have been the result of abrupt changes, but this does not
prove that the characters themselves have been produced with equal
suddenness. On the contrary, Darwin shows very convincingly that a
modification may well be developed by a series of steps, and afterwards
suddenly disappear. Many monstrosities, such as those represented by
twisted stems, furnish direct proofs in support of this view, since they
are produced by the loss of one character and this loss implies secondary
changes in a large number of other organs and qualities.

Darwin criticises in detail the hypothesis of great and abrupt changes and
comes to the conclusion that it does not give even a shadow of an
explanation of the origin of species. It is as improbable as it is
unnecessary.

Sports and spontaneous variations must now be considered. It is well known
that they have produced a large number of fine horticultural varieties.
The cut-leaved maple and many other trees and shrubs with split leaves are
known to have been produced at a single step; this is true in the case of
the single-leaf strawberry plant and of the laciniate variety of the
greater celandine: many white flowers, white or yellow berries and
numerous other forms had a similar origin. But changes such as these do
not come under the head of adaptations, as they consist for the most part
in the loss of some quality or organ belonging to the species from which
they were derived. Darwin thinks it impossible to attribute to this cause
the innumerable structures, which are so well adapted to the habits of life
of each species. At the present time we should say that such adaptations
require progressive modifications, which are additions to the stock of
qualities already possessed by the ancestors, and cannot, therefore, be