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 explained on the ground of
a supposed analogy with sports, which are for the most part of a
retrogressive nature.

Excluding all these more or less sudden changes, there remains a long
series of gradations of variability, but all of these are not assumed by
Darwin to be equally fit for the production of new species. In the
first place, he disregards all mere temporary variations, such as size,
albinism, etc.; further, he points out that very many species have
almost certainly been produced by steps, not greater, and probably not
very much smaller, than those separating closely related varieties. For
varieties are only small species. Next comes the question of polymorphic
species: their occurrence seems to have been a source of