2. They therefore require in some way or other a special balance of protection.
3. Now, if the male and female were distinct species, with different habits and organisations, you would, I think, at once admit that a difference of colour serving to make that one less conspicuous which evidently required more protection than the other had been acquired by Natural Selection.
4. But you admit that variations appearing in one sex are transmitted (often) to that sex only: there is therefore [pg 224]nothing to prevent Natural Selection acting on the two sexes as if they were two species.
5. Your objection that the same protection would to a certain extent be useful to the male, seems to me utterly unsound, and directly opposed to your own doctrine so convincingly urged in the "Origin," "that Natural Selection never can improve an animal beyond its needs." So that admitting abundant variation of colour in the male, it is impossible that he can be brought by Natural Selection to resemble the female (unless her variations are always transmitted to him), because the difference of their colours is to balance the difference in their organisations and habits, and Natural Selection cannot give to the male more than is needed to effect that balance.
6. The fact that in almost all protected groups the females perfectly resemble the males shows, I think, a tendency to transference of colour from one sex to the other when this tendency is not injurious.
Or perhaps the protection is acquired because this tendency exists. I admit therefore in the case of concealed nests they [habits] may have been acquired for protection.
Now for the special case.
7. In the very weak-flying Leptalis both sexes mimic Heliconidæ.
8. In the much more powerful Papilio, Pieris, and Diadema it is generally the female only that mimics Danaida.
9. In these cases the females often acquire more bright and varied colours than the male. Sometimes, as in Pieris pyrrha, conspicuously so.