Species and Varieties, Their Origin by Mutation | Page 8

This may
be inferred from what we have already seen concerning the two
opposing theories, derived and isolated from Darwin's original broad

conception. One of them considers mutations as the origin of new
forms, while the other assumes fluctuations to be the source of all
evolution.
As mentioned above, my own experience has led me to accept the first
view. Therefore I shall have to show that mutations do yield new and
constant forms, while fluctuations are not adequate to do so. Retrograde
varieties and elementary species may both be seen to be produced by
sudden mutations. Varieties have often been observed to appear at once
and quite unexpectedly in horticulture and agriculture, and a survey of
these historical facts will be the subject of one of my lectures. In some
instances I have succeeded in repeating these observations in my
garden under the strict conditions of a scientific experiment, and these
instances teach us the real nature of the process of mutation in all its
visible features. New elementary [17] species are far more rare, but I
have discovered in the great evening-primrose, or Oenothera
lamarckiana a strain which is producing them yearly in the wild state
as well as in my garden. These observations and pedigree-experiments
will be dealt with at due length in subsequent lectures.
Having proved the existence and importance of mutations, it remains to
inquire how far the improvements may go which are due only to
fluctuating variability. As the term indicates, this variability is
fluctuating to and fro, oscillating around an average type. It never fails
nor does it, under ordinary circumstances, depart far from the fixed
average.
But the deviation may be enlarged by a choice of extremes. In sowing
their seed, the average of the strain is seen to be changed, and in
repeating the experiment the change may be considerable. It is not clear,
whether theoretically by such an accumulation, deviations might be
reached which could not be attained at once in a single sowing. This
question is hardly susceptible of an experimental answer, as it would
require such an enormous amount of seed from a few mother plants as
can scarcely ever be produced.
The whole character of the fluctuations shows them to be of an
opposite nature, contrasting [18] manifestly with specific and varietal
characters. By this method they may be proved to be inadequate ever to
make a single step along the great lines of evolution, in regard to
progressive as well as to retrograde development.

First of all fluctuations are linear, amplifying or lessening the existing
qualities, but not really changing their nature. They are not observed to
produce anything quite new, and evolution of course, is not restricted to
the increase of the already existing peculiarities, but depends chiefly on
the continuous addition of new characters to the stock. Fluctuations
always oscillate around an average, and if removed from this for some
time, they show a tendency to return to it. This tendency, called
retrogression, has never been observed to fail, as it should, in order to
free the new strain from the links with the average, while new species
and new varieties are seen to be quite free from their ancestors and not
linked to them by intermediates.
The last few lectures will be devoted to questions concerning the great
problem of the analogy between natural and artificial selection. As
already stated, Darwin made this analogy the foundation stone of his
theory of descent, and he met with the severest objections and
criticisms precisely on this point. But I hope to [19] show that he was
quite right, and that the cause of the divergence of opinions is due
simply to the very incomplete state of knowledge concerning both
processes. If both are critically analyzed they may be seen to comprise
the same factors, and further discussion may be limited to the
appreciation of the part which each of them has played in nature and
among cultivated plants.
Both natural and artificial selection are partly specific, and partly
intra-specific or individual. Nature of course, and intelligent men first
chose the best elementary species from among the swarms. In
cultivation this is the process of variety-testing. In nature it is the
survival of the fittest species, or, as Morgan designates it, the survival
of species in the struggle for existence. The species are not changed by
this struggle, they are only weighed against each other, the weak being
thrown aside.
Within the chosen elementary species there is also a struggle. It is
obvious, that the fluctuating variability adapts some to the given
circumstances, while it lessens the chances of others. A choice results,
and this choice is what is often exclusively called selection, either
natural or artificial. In cultivation it produces the improved and the
local races; in