CHAPTER V
SOME CRITICISMS
The facts related in the last two chapters are sufficient to make it clear that these remarkable resemblances between species belonging as a rule to widely different groups constitute a real phenomenon, and as such demand an explanation. One explanation, that in terms of the theory of mimicry, has already been outlined, and we may now turn to consider it in more detail. Some years ago Wallace[[24]], combating the suggestion that these instances of resemblance might be mere coincidences, laid down five conditions which he stated were applicable to all such cases, and rendered utterly inadequate any explanation other than in terms of natural selection. These five conditions are of historical interest and may also serve as a peg for sundry criticisms in connection with the mimicry theory. They are as follows:
(1) That the imitative species occur in the same area and occupy the very same station as the imitated.
(2) That the imitators are always the more defenceless.
(3) That the imitators are always less numerous in individuals.
(4) That the imitators differ from the bulk of their allies.
(5) That the imitation, however minute, is external and visible only, never extending to internal characters or to such as do not affect the external appearance.
In offering certain criticisms of the mimicry explanation it will be convenient to do so in connection with these five conditions which Wallace regarded as constant for all cases of mimetic resemblance.