116 THE INFLUENCE OF INANIMATE SUEEODNDINGS. 



On the other hand, it is difficult to understand how a race of 

 brown animals can be gradually transformed by selection into a 

 variety which always turns snow-white in winter. Granting 

 that a brown weasel could, by any external or internal cause, 

 be changed during the winter into a brown and white spotted 

 one, this weasel would not have the smallest advantage over 

 the brown one in consequence of the white mixture in its fur, 

 for it woiild be quite as conspicuous as a plain brown one in 

 the pure white of the snow, perhaps even more so. That a 

 white vaiiety should arise from a gradual increase of the white 

 patches in the piebald fur is not to be thought of. It might 

 indeed be possible that a selection should be effected, if a pure 

 white variety were at once and from the fii-st produced from 

 the animals which first exhibited this modification of their 

 summer colouring, since these, like the nearly white ones, 

 would in fact enjoy an essential advantage over the brown or 

 spotted ones. But, even then, selection would not have pro- 

 duced this pure white winter colouring by the cumulation of 

 small and useful variations, but have chosen between the two 

 varieties offered, the white and the brown ; and the question as 

 to the origin of the winter colouring is still unanswered. The 

 same arguments hold equally good for all pure white varieties, 

 whether in arctic regions or on the ice and snow of high peaks 

 in mountain chains ; these, like all other species that turn 

 white in winter — it would be superfluous to enumerate them 

 liere '' — cannot have preserved their winter colouring by means 

 of selection ; whereas, no doubt, after other causes, unknown 

 to us, had in the first instance given rise to a constantly white 

 variety, or to one white in winter and brown in summer, this 

 mav have been secured by the rapid extii-pation of the less 

 well-protected brown or spotted varieties. It is thus that 

 Wallace accounts for the occurrence of white species in northern 

 re,<>-ions, but he does not even refer to the question as to how 

 the white hue originated. 



The nature of these causes is in fact unknown ; it was pro- 

 bably an error to assume that in all the above-mentioned cases 

 this whiteness, i.e. the absence of the pigment, was the dii-ect 

 effect of the winter cold, or of the low temperature of the polar 



