Page:The Zoologist, 4th series, vol 4 (1900).djvu/358

328 condition, it is a survival of original assimilative colouration, and not a direct product of natural selection" (p. 473). The question to be considered is, whether these propositions have been sufficiently maintained.

I may here state that, so far as concerns the endeavours of some biologists to make natural selection responsible for every trifling detail of colour, I can sympathise to some extent with Mr. Distant's general attitude; as, for instance, when it is attempted to explain trivial local variations by the purely hypothetical and quite unprovable assumption that these are correlated with certain obscure but useful constitutional characters, of which we know nothing at all, on the ground that it is these characters, and not the trivial colours themselves, that have been operated upon by natural selection. Such contentions certainly do not commend themselve in the present state of our knowledge. But when one contemplates the vast mass of valuable biological work, both in arduous experiments and paisntakingpainstaking [sic] observations, that has been and is still being accomplished by the champions of natural selection in order to test the validity of the Darwinian theory in every hole and corner of the organic world, one can only read with unfeigned astonishment the assertion that "the tendency to explain all problems by natural selection is to-day greatly retarding the study of bionomics. It is not one whit removed from the proferred explanation of the old teleologists, and represents as little thinking"! An endeavour to refute this assertion would be out of place here; and I need only mention, with special reference to the last phrase of the above quotation, that although the explanation on the selection theory of the inter-resemblance of distasteful insects appears simple enough at the present day, yet for twenty years it baffled the ingenuity of such men as Bates and Wallace, until Fritz Müller put forward the ingenious theory of mimicry now associated with his name.

But to return to Mr. Distant's suggestions. We are at once confronted with a difficulty in that no definition is offered of the exact significance of the term "assimilative colouration," which is evidently loosely applied, seeing, for example, that the brilliant red on the wings of the African Touracos is given as an instance of partial assimilative colouration (p. 460), apparently on the assumption that these birds eat copper —the common copper