Now I have been careful thus to present in all its more important details an imaginary argument drawn from inorganic nature, because it furnishes a complete analogy to the actual argument which is drawn from organic nature.  Without any question, the instances of apparent design, or of the apparently intentional adaptation of means to ends, which we meet with in organic nature, are incomparably more numerous and suggestive than anything with which we meet in inorganic nature.  But if once we find good reason to conclude that the former, like the latter, are all due, not to the immediate, special and prospective action of a contriving intelligence (as in watch-making or creation), but to the agency of secondary or physical causes acting under the influence of what we call general laws, then it seems to me that no matter how numerous or how wonderful the adaptations of means to ends in organic nature may be, they furnish one no other or better evidence of design than is furnished by any of the facts of inorganic nature.

For the sake of clearness let us take any special case.  Paley says, ’I know of no better method of introducing so large a subject than that of comparing a single thing with a single thing; an eye, for example, with a telescope.’  He then goes on to point out the analogies between these two pieces of apparatus, and ends by asking, ’How is it possible, under circumstances of such close affinity, and under the operation of equal evidence, to exclude contrivance in the case of the eye, yet to acknowledge the proof of contrivance having been employed, as the plainest and clearest of all propositions in the case of the telescope?’

Well, the answer to be made is that only upon the hypothesis of special creation can this analogy hold:  on the hypothesis of evolution by physical causes the evidence in the two cases is not equal.  For, upon this hypothesis we have the eye beginning, not as a ready-made structure prepared beforehand for the purposes of seeing, but as a mere differentiation of the ends of nerves in the skin, probably in the first instance to enable them better to discriminate changes of temperature.  Pigment having been laid down in these places the better to secure this purpose (I use teleological terms for the sake of brevity), the nerve-ending begins to distinguish between light and darkness.  The better to secure this further purpose, the simplest conceivable form of lens begins to appear in the shape of small refractive bodies.  Behind these sensory cells are developed, forming the earliest indication of a retina presenting a single layer.  And so on, step by step, till we reach the eye of an eagle.