A definite answer to the latter question ought not to be expected,
seeing that no one can solve the simpler problem, why, of two races of
savages, one has risen higher in the scale of civilisation than the other;
and this apparently implies increased brain power.
We will return to Mr. Mivart's other objections. Insects often resemble
for the sake of protection various objects, such as green or decayed
leaves, dead twigs, bits of lichen, flowers, spines, excrement of birds,
and living insects; but to this latter point I shall hereafter recur. The
resemblance is often wonderfully close, and is not confined to colour, but
extends to form, and even to the manner in which the insects hold
themselves. The caterpillars which project motionless like dead twigs from
the bushes on which they feed, offer an excellent instance of a resemblance
of this kind. The cases of the imitation of such objects as the excrement
of birds, are rare and exceptional. On this head, Mr. Mivart remarks, "As,
according to Mr. Darwin's theory, there is a constant tendency to
indefinite variation, and as the minute incipient variations will be in ALL
DIRECTIONS, they must tend to neutralize each other, and at first to form
such unstable modifications that it is difficult, if not impossible, to see
how such indefinite oscillations of infinitesimal beginnings can ever build
up a sufficiently appreciable resemblance to a leaf, bamboo, or other
object, for natural selection to seize upon and perpetuate.
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