er'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