We are not at all sure that no facts are against the theory of protective
mimicry. We shall presently set forth some which to us seem, if not
actually inconsistent with the theory, at least to point to the
conclusion that the phenomenon may be explained otherwise than as a
product of natural selection.
Evidence for the Theory
Let us first briefly state the case for the theory of protective mimicry.
1. It is asserted that the mimicking species and that which is mimicked
are often not nearly related. For example, the unpalatable larva of the
Cinnabar Moth (_Euchelia jacobaeæ_) is said to mimic a wasp, because it
has black and yellow rings round its body.
“The conclusion which emerges most clearly,” writes Poulton (p. 232), “is
the entire independence of zoological affinity exhibited by these
resemblances.” This is supposed to be proof that Darwin was wrong when he
asserted that the original likeness was due to affinity. Says Poulton:
“The preservation of an original likeness due to affinity undoubtedly
explains certain cases of mimicry, but we cannot appeal to this principle
in the most remarkable instances.”
2. It is asserted that species which are mimicked are invariably either
armed with a sting, well defended, or unpalatable, so that it is against
the interest of insectivorous creatures to attack them. It is further
asserted that the species imitated are “even more unpalatable than the
generality of their order.”
3. It is pointed out that the most distasteful groups of butterflies—the
_Danaidæ_, the _Acræinæ_, the _Ithomiinæ_, and the _Heliconinæ_—consist
of large numbers of species which closely resemble one another. This is
said to be due to Müllerian mimicry. Mayer states that in South America
there are 450 species of inedible _Ithomiinæ_ which display only 15
distinct colours, while the 200 species of _Papilio_, which are edible,
exhibit 36 distinct colours. Nevertheless, he says, there is no lack of
individual variability among the former hence their conservatism as
regards colour cannot be attributed to their having but little tendency
to vary.
4. It is asserted that although in many cases the mimetic resemblances
extend to the minutest detail, nevertheless they are not accompanied by
any changes in the mimetic species except such as assist in the
production or strengthening of a superficial likeness.
Pictures illustrating such cases of mimicry are figured on pp. 241, 247,
and 251 of Wallace’s _Darwinism_ (1890 edition).
5. It is stated that mimetic resemblance is not confined to colour, but
extends to pattern, form, attitude, and movement; that deep-seated organs
are affected when the superficial resemblance is intensified, but not
otherwise. Poulton cites _Clytus arietis_, the “wasp-beetle,” as an
example of this.
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