For the rest, Mr. Spencer’s articles have relieved me from the necessity of going into the evidence which proves that such structures as a giraffe’s neck, for example, cannot possibly have been produced by the accumulation of variations which had their origin mainly in accident. There is no occasion to add anything to what Mr. Spencer has said on this score, and I am satisfied that those who do not find his argument convince them would not be convinced by anything I might say; I shall, therefore, omit what I had written on this subject, and confine myself to giving the substance of Mr. Spencer’s most telling argument against Mr. Darwin’s theory that accidental variations, if favourable, would accumulate and result in seemingly adaptive structures. Mr. Spencer well shows that luck or chance is insufficient as a motive-power, or helm, of evolution; but luck is only absence of design; if, then, absence of design is found to fail, it follows that there must have been design somewhere, nor can the design be more conveniently placed than in association with function.
Mr. Spencer contends that where life is so simple as to consist practically in the discharge of only one function, or where circumstances are such that some one function is supremely important (a state of things, by the way, more easily found in hypothesis than in nature—at least as continuing without modification for many successive seasons), then accidental variations, if favourable, would indeed accumulate and result in modification, without the aid of the transmission of functionally produced modification. This is true; it is also true, however, that only a very small number of species in comparison with those we see around us could thus arise, and that we should never have got plants and animals as embodiments of the two great fundamental principles on which it is alone possible that life can be conducted, { 107a} and species of plants and animals as embodiments of the details involved in carrying out these two main principles.
If the earliest organism could have only varied favourably in one direction, the one possible favourable accidental variation would have accumulated so long as the organism continued to exist at all, inasmuch as this would be preserved whenever it happened to occur, while every other would be lost in the struggle of competitive forms; but even in the lowest forms of life there is more than one condition in respect of which the organism must be supposed sensitive, and there are as many directions in which variations may be favourable as there are conditions of the environment that affect the organism. We cannot conceive of a living form as having a power of adaptation limited to one direction only; the elasticity which admits of a not being “extreme to mark that which is done amiss” in one direction will commonly admit of it in as many directions as there are possible favourable modes of variation; the number of these, as has been just said, depends upon the number of the conditions of the environment that affect the organism, and these last, though in the long run and over considerable intervals of time tolerably constant, are over shorter intervals liable to frequent and great changes; so that there is nothing in Mr. Charles Darwin’s system of modification through the natural survival of the lucky, to prevent gain in one direction one year from being lost irretrievably in the next, through the greater success of some in no way correlated variation, the fortunate possessors of which alone survive. This, in its turn, is as likely as not to disappear shortly through the arising of some difficulty in some entirely new direction, and so on; nor, if function be regarded as of small effect in determining organism, is there anything to ensure either that, even if ground be lost for a season or two in any one direction, it shall be recovered presently on resumption by the organism of the habits that called it into existence, or that it shall appear synchronously in a sufficient number of individuals to ensure its not being soon lost through gamogenesis.