46 COLOUR VARIATION IN BRITISH ADDERS. 



suppose that adders living on bare mountain sides, or sandy 

 heaths, will be of a light colour, showing the colours of brown, 

 or reddish shades, or golden, and, indeed, I ought to say at once 

 that the theory that colour variation in adders is mainly due to 

 the locality is the one apparently accepted. Personally, I do not 

 believe it to be the true explanation, and I shall try and give 

 good reasons for my disbelief in it. The locality theory is 

 suggested by the analogy of colour variation in fish. Thus, a 

 correspondent writes to me, saying: "The different colours of 

 adders are due, I think, to the precise spot they frequent, just as 

 trout vary within a few yards in the same stream, one taken out 

 of a deep hole being of a darker colour than one from a 

 shallow rapid." Very plausible, but, in the case of adders, I am 

 afraid not true. I say nothing about fish, as I know nothing 

 about their colour variation. But the crucial test of this theory 

 is this : if locality determines the colour of adders, then all 

 adders taken in the same locality ought to show the same 

 colouring. Anyone who has made even a small collection of his 

 local adders knows that this is far from being the case ; indeed, 

 probably finds that no two are exactly alike, while some are 

 strikingly different from others taken in the same spot. If this 

 be true, and it cannot be denied, then it follows that locality 

 fails to provide the explanation. Had I my own local collection 

 here, I could show you every variety of colour variations in 

 adders in specimens all taken from one hill, and I have not the 

 slightest hesitation in saying that it is utterly impossible to tell 

 from the colour of an adder the nature of the ground from 

 whence the specimen came. It might be that a number of 

 adders from one place might show some similarity in colouring, 

 but they would also show great variation, and my argument is 

 that, while the locality might account for the resemblance, it 

 cannot possibly account for the differences. I will go further and 

 say that, if any great resemblance is noticed, it will be found to 

 be accounted for by the two facts which we have yet to consider. 

 So far, then, we have arrived at this point, that a collection of 

 adders in any given district shows a wide colour variation ; 



