For the sake of clearness I have assumed that the physical causes with which we are already acquainted are sufficient to explain the observed phenomena of organic nature.  But it clearly makes no difference whether or not this assumption is conceded, provided we allow that the observed phenomena are all due to physical causes of some kind, be they known or unknown.  That is to say, in whatever measure we exclude the hypothesis of the direct or immediate intervention of the Deity in organic nature (miracle), in that measure we are reducing the evidence of design in organic nature to precisely the same logical position as that which is occupied by the evidence of design in inorganic nature.  Hence I conceive that Mill has shown a singular want of penetration where, after observing with reference to natural selection, ’creative forethought is not absolutely the only link by which the origin of the wonderful mechanism of the eye may be connected with the fact of sight,’ he goes on to say, ’leaving this remarkable speculation (i.e. that of natural selection) to whatever fate the progress of discovery may have in store for it, in the present state of knowledge the adaptations in nature afford a large balance of probability in favour of creation by intelligence.’  I say this passage seems to me to show a singular want of penetration, and I say so because it appears to argue that the issue lies between the hypothesis of special design and the hypothesis of natural selection.  But it does not do so.  The issue really lies between special design and natural causes.  Survival of the fittest is one of these causes which has been suggested, and shown by a large accumulation of evidence to be probably a true cause.  But even if it were to be disproved as a cause, the real argumentative position of teleology would not thereby be effected, unless we were to conclude that there can be no other causes of a secondary or physical kind concerned in the production of the observed adaptations.

I trust that I have now made it sufficiently clear why I hold that if we believe the reign of natural law, or the operation of physical causes, to extend throughout organic nature in the same universal manner as we believe this in the case of inorganic nature, then we can find no better evidence of design in the one province than in the other.  The mere fact that we meet with more numerous and apparently more complete instances of design in the one province than in the other is, ex hypothesi, merely due to our ignorance of the natural causation in the more intricate province.  In studying biological phenomena we are all at present in the intellectual position of our imaginary teleologist when studying the marine bay:  we do not know the natural causes which have produced the observed results.  But if, after having obtained a partial key in the theory of natural selection, we trust to the large analogy which is afforded by the simpler provinces of Nature, and conclude that