The Making of Species 



of explanation ; but, on the assumption that a 

 slight rearrangement of the biological atoms in 

 the molecule may produce very diverse results, as 

 we see in the case of chemical molecules, and 

 of seasonally dimorphic butterflies, there is 

 no particular ground for surprise at such a 

 phenomenon. 



In this connection we may cite the significant 

 fact, so well known to canary breeders, that two 

 crested birds when mated tend to produce a bald- 

 headed one. 



If the colour of any part of an organism be 

 due to the internal arrangement of the constituent 

 parts of the biological molecule from which it is 

 derived, we should expect any rearrangement of 

 the component parts to produce quite a different 

 colour. In other words, we should expect occa- 

 sionally to see colour-mutations. These are pre- 

 cisely what we do see. Similarly, if the scheme 

 of colouring of an organism be due to a certain 

 grouping of biological molecules, we should ex- 

 pect the same scheme of colouring to occur in 

 organisms which are not nearly related. This, 

 too, we observe in nature. 



Many of the phenomena of mimicry, and all 

 the cases which we have cited as pseudo-mimicry, 

 seem to us to be referable to this. 



Take, for example, the magpie colouration in 

 birds that is to say, a scheme of colouring in 

 which the body is white, and head, wings, and 



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