physical causes are everywhere concerned in the production of organic structures, then we have concluded that any evidence of design which these structures present is of just the same logical value as that which we may attach to the evidence of design in inorganic nature.  If it should still be urged that the adaptations met with in organic nature are from their number and unity much more suggestive of design than anything met with in inorganic nature, I must protest that this is to change the ground of argument and to evade the only point in dispute.  No one denies the obvious fact stated:  the only question is whether any number and any quantity of adaptations in any one department of nature afford other or better evidence of design than is afforded by adaptations in other departments, when all departments alike are supposed to be equally the outcome of physical causation.  And this question I answer in the negative, because we have no means of ascertaining the extent to which the process of natural selection, or any other physical cause, is competent to produce adaptations of the kind observed.

Thus, to take another instance of apparent design from inorganic nature, it has been argued that the constitution of the atmosphere is clearly designed for the support of vegetable and animal life.  But before this conclusion can be established upon the facts, it must be shown that life could exist under no other material conditions than those which are furnished to it by the elementary constituents of the atmosphere.  This, however, it is clearly impossible to show.  For anything that we can know to the contrary, life may actually be existing upon some of the other heavenly bodies under totally different conditions as to atmosphere; and the fact that on this planet all life has come to be dependent upon the gases which occur in our atmosphere, may be due simply to the fact that it was only the forms of life which were able to adapt themselves (through natural selection or other physical causes) to these particular gases which could possibly be expected to occur—­just as in matters of still smaller detail, it was only those forms of life that were suited to their several habitats in the marine bay, which could possibly be expected to be found in these several situations.  Now, if a set of adjustments so numerous and so delicate as those on which the relations of every known form of life to the constituent gases of the atmosphere are seen to depend, can thus be shown not necessarily to imply the action of any disposing intelligence, how is it possible to conclude that any less general exhibitions of adjustment imply this, so long as every case of adjustment, whether or not ultimately due to design, is regarded as proximately due to physical causes?