Having unwittingly shown that lessened use of closely-connected and
co-operative parts does not cause concomitant variation in these parts,
Mr. Spencer concludes that the concomitant variation requisite for
evolution can only be caused by altered degrees of use or disuse. He
elaborately argues that the many co-ordinated modifications of parts
necessitated by each important alteration in an animal are so complex
that they cannot possibly be brought about except by the inherited
effect of the use and disuse of the various parts concerned. He holds,
for instance, that natural selection is inadequate to effect the
numerous concomitant changes necessitated by such developments as that
of the long neck of the giraffe. Darwin, however, on the contrary, holds
that natural selection alone "would have sufficed for the production of
this remarkable quadruped."[8] He is surprised at Mr. Spencer's view
that natural selection can do so little in modifying the higher animals.
Thus one of the chief arguments with which Mr. Spencer supports his
theory is so poorly founded as to be rejected by a far greater authority
on such subjects. All that is needed is that natural selection should
preserve the tallest giraffes through times of famine by their being
able to reach otherwise inaccessible stores of foliage. The continual
variability of all parts of the higher animals gives scope for
innumerable changes, and Nature is not in a hurry. Mr. Spencer, however,
says that "the chances against any adequate readjustments fortuitously
arising must be infinity to one." But he has also shown that altered
degree of use does not cause the needed concomitant variation of
co-operative parts. So the chances against a beneficial change in an
animal must be, at a liberal estimate, infinity to two. Mr. Spencer, if
he has proved anything, has proved that it is practically impossible
that the giraffe can have acquired a long neck, or the elk its huge
horns, or that any species has ever acquired any important modification.
Mr. Wallace, in his _Darwinism_, answers Mr. Spencer by a collection of
facts showing that "variation is the rule," that the range of variation
in wild animals and plants is much greater than was supposed, and that
"each part varies to a considerable extent independently" of other
parts, so that "the materials constantly ready for natural selection to
act upon are abundant in quantity and very varied in kind." While
co-operative parts would often be more or less correlated, so that they
would tend to vary together, coincident variation is not necessary. The
lengthened wing might be gained in one generation, and the strengthened
muscle at a subsequent period; the bird in the meanwhile drawing upon
its surplus energy, aided (as I would suggest) by the strengthening
effect of increased use in the individual. Seeing that artificial
selection of complicated variations has modified animals in many points
either simultaneously or by slow steps, as with otter-sheep, fancy
pigeons, &c. (many of the characters thus obtained being clearly
independent of use and disuse), natural selection must be credited with
similar powers, and Mr. Wallace concludes that Mr. Spencer's
insuperable difficulty is "wholly imaginary."
The extract concerning a somewhat similar "class of difficulties," which
Mr. Spencer quotes from his _Principles of Biology_, is faulty in its
reasoning,[9] though legitimate in its conclusion concerning the
increasing difficulty of evolution in proportion with the increasing
number and complexity of faculties to be evolved. But this increasing
difficulty of complex evolution is only overcome by _some_
favourably-varying individuals and species--not by all. And as the
difficulty increases we find neglect and decay of the less-needed
faculties--as with domesticated animals and civilized men, who lose in
one direction while they gain in another. The increasing difficulty of
complex evolution by natural selection is no proof whatever of
use-inheritance[10] except to those who confound difficulty with
impossibility.