The opposing argument is repeated and passed in another form: 

“The evidence of design afforded by the marks of adaptation in works of human competence is null and void in the case of creation itself . . .  Nature is full of adaptations; but these are valueless to us as traces of design, unless we know something of the rival adaptations among which an intelligent being might have chosen.  To assert that in Nature no such rival adaptations existed, and that in every case the useful function in question could be established by no other instrument but one, is simply to reason in a circle, since it is solely from what we find existing that our notions of possibility and impossibility are drawn. . . .  We cannot imagine ourselves in the position of the Creator before his work began, nor examine the materials among which he had to choose, nor count the laws which limited his operations.  Here all is dark, and the inference we draw from the seeming perfections of the existing instruments or means is a measure of nothing but our ignorance.”

But the question is not about the perfection of these adaptations, or whether others might have been instituted in their place.  It is simply whether observed adaptations of intricate sorts, admirably subserving uses, do or do not legitimately suggest to one designing mind that they are the product of some other.  If so, no amount of ignorance, or even inconceivability, of the conditions and mode of production could affect the validity of the inference, nor could it be affected by any misunderstanding on our part as to what the particular use or function was; a statement which would have been deemed superfluous, except for the following: 

“There is not an organ in our bodies but what has passed, and is still passing, through a series of different and often contradictory interpretations.  Our lungs, for instance, were anciently conceived to be a kind of cooling apparatus, a refrigerator; at the close of the last century they were supposed to be a centre of combustion; and nowadays both these theories have been abandoned for a third . . .  Have these changes modified in the slightest degree the supposed evidence of design?”

We have not the least idea why they should.  So, also, of complicated processes, such as human digestion, being replaced by other and simpler ones in lower animals, or even in certain plants.  If “we argue the necessity of every adaptation solely from the fact that it exists,” and that “we cannot mutilate it grossly without injury to the function,” we do not “announce triumphantly that digestion is impossible in any way but this,” etc., but see equal wisdom and no impugnment of design in any number of simpler adaptations accomplishing equivalent purposes in lower animals.

Finally, adaptation and utility being the only marks of design in Nature which we possess, and adaptation only as subservient to usefulness, the Westminster Reviewer shows us how: