Theory of Protective Mimicry
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).