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.
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