The Making of Species 
These proportionate advantages are inversely in 
the duplicate ratio of the respective percentages 
that would have survived without the mimicry.’” 
This is rather a cumbrous method of saying 
that if there are in a locality a number of young 
birds, and each of these has to learn by ex- 
perience which insects are edible and which are 
not, each will, if it learns by one example, devour 
one insect of any given pattern. Now, if two 
species of inedible insects have this pattern, they 
will between them lose only one member in the 
educating process of each bird, whereas if each 
species of insect had a colouration peculiar to 
itself, each species would lose a whole individual 
instead of half a one. There can be no doubt 
that such a livery of unpalatability is of some 
advantage to its possessors. 
It has been shown experimentally that hand- 
reared young birds have to acquire their know- 
ledge of flavours and colours by experiment. 
It is well known that in many species the 
male and the female are not coloured alike. 
Such species are said to exhibit sexual 
dimorphism. In these cases it is usually 
the male that is more conspicuously coloured. 
Darwin felt that the theory of natural selection 
could not satisfactorily account for this phe- 
nomenon, so put forward the supplementary 
theory of sexual selection. On this hypothesis 
the females are supposed to be able to pick and 
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