Reginald Crundall Punnett

“ If birds regarded white butterflies as edible it is difficult to suppose that they would be checked in their attacks by a trifling patch of colour while the main ground of the insect was still white. But unless they avoided those with the small colour patch there would be an end of natural selection in so far as the patch was concerned, and it would have no opportunity of developing further through the operation of that factor. This is the difficulty of the initial variation which has been clearly recognised by most of the best known supporters of the theory of mimicry. ”

“ Let us suppose that in the same area live two equally distasteful species A and B, each with a conspicuous though distinct warning pattern, and each sacrificing 1000 individuals yearly to the education of young birds. Further let it be supposed that A is a common species of which there are 100,000 individuals in the given area, while B is much rarer, and is represented by 5000. The toll exacted by young birds falls relatively more lightly upon A than upon B, for A loses only 1%, whereas B's loss is 20%. ”

“ If a sport occurred which was sufficiently similar to an unpalatable species to be confused with it, it is theoretically demonstrable that, although relatively scarce to start with, it would rapidly increase at the expense of the unprotected male-like female until the latter was eliminated. ”

“ The mortality among the mimetic members of A is six times as great as among those which retain the type form. It is clear therefore that a variation of A which can be mistaken for B is at a great disadvantage as compared with the type form [7] , and consequently it must be supposed that the Müllerian factor, as the destruction due to experimental tasting by young birds is termed, cannot bring about a resemblance on the part of a more numerous to a less numerous species. ”

“ Natural selection does not originate the likeness, but, as soon as a rough one has made its appearance, it comes into operation and works it up through intermediate stages into the finished portrait. It still plays some part in the formation of a mimetic resemblance though its rôle is now restricted to the putting on of the finishing touches. Those who take this view hold also that the continued action of natural selection is necessary in order to keep the likeness up to the mark. ”

“ But if such sports can be produced suddenly by some mutational process not at present understood, why should not these sports be the females of the three mimicking species as we see them at present? Why need we suppose that there were intermediate stages between the mimicking female and the original hypothetical female which was like the male? ”

“ Suppose that of the 100,000 individuals of A 10,000 shewed a variation which led to their being mistaken for B, so that there are 90,000 of the A pattern and 15,000 of the B pattern of which 10,000 belong to species A. A will now lose 1000 out of the 90,000 having the A pattern, and 2⁄3 × 1000 out of the 10,000 of species A which exhibit the B pattern. The toll of the birds will be 1⁄90 of those keeping the original A pattern, and 2⁄30 of those of species A which have assumed the B pattern. ”

“ But Argynnis hyperbius is also a species in which the female mimics D. plexippus; and by using the same argument as that just detailed for Elymnias undularis we can shew that the Danaine model, D. plexippus, must also have been like the male of Argynnis hyperbius. And if the resemblance of A. hyperbius was developed subsequently to that of E. undularis, then both D. plexippus and E. undularis must at one time have been like the male of A. hyperbius, a proposition to which few entomologists are likely to assent. ”

“ Bates himself offered no suggestion as to the way in which such a form as a Pierid could be conceived of as beginning to resemble an Ithomiine [1] . Wallace supposed that the Ithomiines were to start with not so distinct from many of the edible forms as they are to-day, and that some of the Pierines inhabiting the same district happened to be sufficiently like some of the unpalatable forms to be mistaken for them occasionally [2] . ”

“ Clearly if some members of B varied so that they could be mistaken for A it would be greatly to their advantage, since they would pass from a population in which the destruction by young birds was 20% to one in which it would now be rather less than 1%. ”

“ It should be observed that the process of imitation probably never commenced between forms widely dissimilar in colour. But starting with species already somewhat like each other, the closest resemblance, if beneficial, could readily be gained by the above means ”