Wallace. Danvinism. pp. 252-7. 
197 
Yet this can hardly be true mimicry, because all are alike protected 
by the nauseous secretion which renders them unpalatable to birds.” 
—(Wallace. Tropical Nature, pp. 256-7.) 
The imitation of a protected species by another species 
also protected was thus explained by Dr. Fritz Muller, 
in 1879. He assumed that insect-eating birds only learn' 
from experience to distinguish the edible from the inedible 
butterflies, and in doing so necessarily sacrifice a certain 
number of the latter. The quantity of insectivorous birds 
in tropical America is enormous, and the number of young 
birds which every year have to learn wisdom by expe 
rience as regards the species of butterflies to be caught 
or avoided is so great that the sacrifice of life of the 
inedible species must be considerable, and, to a compara 
tively weak or scarce species, of vital importance. “If two 
species are so much alike as to be mistaken for one 
another, the fixed number annually sacrificed by inex 
perienced birds will be divided between them, and both 
will benefit. But if the two species are very unequal 
in numbers the benefit will be comparatively slight for 
the more abundant species, but very great for the rare 
one. To the latter it may make all the difference between 
safety and destruction.”* 
We may observe, in passing, that if this were a satis 
factory explanation of the fact that protected species 
mimic protected species, it would leave quite unexplained 
the phenomenon of unprotected species mimicking unpro 
tected species ; and we should still have resemblance of 
coloration brought about apart from Natural Selection. 
But the explanation of the resemblance between protected 
species is not altogether convincing. We question whether 
young birds are left to learn what to eat and avoid from