Reply to Mr Wallace's Theory of Birds' Nests 143 



birds, intelligent modification of the ordinary construction of their 

 nests is by no means rare under exceptional circumstances. 



Mr Wallace and Mr Bates have, with their usual ability, argued 

 also for natural selection as the explanation of the instances of 

 mimicry or disguise which are to be met with in many animals, 

 such as moths pretending to be bees, flies to be wasps, and gener- 

 ally the resemblance which exists between the colour of animated 

 beings and that of the scenery in which they live— white in snowy 

 regions, sand-coloured in sandy-deserts, heath-coloured in moors, 

 and so on. These, however, do not appear to belong to the same 

 category of phenomena as the sexual differences in plumage above 

 referred to. In sexual differences the theory relates to modifica- 

 tion of colour previously existing; in mimicry to the causes by 

 which it is originally determined. It is part of the Darwinian 

 theory that surrounding objects and extraneous circumstances are 

 without influence on the development of structure, or on the appear- 

 ance of species produced among them. We do not see that such 

 a belief is essential to that hypothesis ; for although, if it were once 

 admitted that such causes had some influence, it would not be easy 

 to say where it stopped, still it would always leave natural selec- 

 tion and the struggle for life full scope for work. The fact is, 

 however, that unless he has changed his mind, Mr Darwin holds 

 that surrounding objects or conditions have no determinate influ- 

 ence on the formation of species. The wonderful resemblance 

 between the colour of the ground and that of the animals which 

 inhabit it, seems to us to furnish at least a prima facie case to the 

 contrary ; and seeing that neither view has any direct evidence to 

 offer in its favour, it seems to us more reasonable to suppose that 

 an adjustment of the particles of colour in harmony with surrounding 

 colours should be inherent in the laws regulating its development, 

 than that all animals have come to wear the colour of the scenery in 

 which they live, by those which were produced of any other colour 

 having been wiped off as less fitted for surrounding conditions. 

 It is a strong call on our faith to admit that power of natural selection 

 to extend not only to making the colour once for all, but to vary- 

 ing it regularly twice every year, as in the case of many animals 

 inhabiting arctic regions. 



Every artist, every admirer of scenery, is familiar with the har- 

 mony of colour in nature. We do not believe that this is fortuitous. 

 It seems as if there were a polarization of colour as there is of 

 magnetism and electricity, which reduces everything into harmony. 



