54 The Selection Theory 
The strongest of all proofs of the theory, however, is afforded by 
cases of true “mimicry,” those adaptations discovered by Bates: in 
1861, consisting in the imitation of one species by another, which 
becomes more and more like its model. The model is always a 
species that enjoys some special protection from enemies, whether 
because it is unpleasant to taste, or because it is in some way 
dangerous. 
It is chiefly among insects and especially among butterflies that 
we find the greatest number of such cases. Several of these have 
been minutely studied, and every detail has been investigated, so 
that it is difficult to understand how there can still be disbelief in 
regard to them. If the many and exact observations which have been 
carefully collected and critically discussed, for instance by Poulton’, 
were thoroughly studied, the arguments which are still frequently 
urged against mimicry would be found untenable; we can hardly 
hope to find more convincing proof of the actuality of the processes 
of selection than these cases put into our hands. The preliminary 
postulates of the theory of mimicry have been disputed, for instance, 
that diurnal butterflies are persecuted and eaten by birds, but ob- 
servations specially directed towards this point in India, Africa, 
America and Europe have placed it beyond all doubt. If it were 
necessary I could myself furnish an account of my own observations 
on this point. 
In the same way it has been established by experiment and 
observation in the field that in all the great regions of distribution 
there are butterflies which are rejected by birds and lizards, their 
chief enemies, on account of their unpleasant smell or taste. These 
butterflies are usually gaily and conspicuously coloured and thus—as 
Wallace first interpreted it—are furnished with an easily recognisable 
sign: a sign of unpalatableness or warning colours. If they were 
not thus recognisable easily and from a distance, they would fre- 
quently be pecked at by birds, and then rejected because of their 
unpleasant taste; but as it is, the insect-eaters recognise them at 
once as unpalatable booty and ignore them. Such immune? species, 
wherever they occur, are imitated by other palatable species, which 
thus acquire a certain degree of protection. 
It is true that this explanation of the bright, conspicuous colours 
is only a hypothesis, but its foundations,—unpalatableness, and the 
liability of other butterflies to be eaten,—are certain, and its con- 
sequences—the existence of mimetic palatable forms—confirm it in 
the most convincing manner. Of the many cases now known I select 
1 Essays on Evolution, 1889—1907, Oxford, 1908, passim, e.g. p. 269. 
; ® The expression does not refer to all the enemies of this butterfly ; against ichneumon- 
flies, for instance, their unpleasant smell usually gives no protection. 
