It is true that the cause may then seem beyond our grasp. Already the finalist theory of life eludes all pre- cise verification, 'What if we go beyond it in one of its directions? Here, in fact, after a necessary digression, we are back at the question which we regard as essential: can the insufficiency of mechanism be proved by facts? We said that if this demonstration js possible, it is on con- dition of frankly accepting the evolutionist hypothesis, We must now show that if mechanism is insufficient to account for evolution, the way of proving this insufficiency is not to stop at the classic conception of finality, still less to contract or attenuate it, but, on the contrary, to go further.
Let us indicate at once the principle of our demonstration. We said of life that, from its origin, it is the continuation of one and the same impetus, divided into divergent lines of evolution. Something has grown, something has de- veloped by a series of additions which have been so many creations. This very development has brought about a dissociation of tendencies which were unable to grow be- yond a certain point without becoming mutually incom- patible. Strictly speaking, there is nothing to prevent our imagining that the evolution of life might have taken place in one single individual by means of a series of trans- formations spread over thousands of ages. Or, instead of a single individual, any number might be supposed, succeeding each other in a unilinear series. In both cases evolution would have had, so to speak, one dimension only. But evolution has actually taken place through millions of individuals, on divergent lines, each ending at a crossing from which new paths radiate, and so on indefinitely. If
KJhS^j
our hypothesis is justified, if the essential causes working along these diverse roads are of psychological nature, they must keep something in common in spite of the divergence of their effects, as school-fellows long separated keep the same memories of boyhood. Roads may fork or by-waya be opened along which dissociated elements may evolve in an independent manner, but nevertheless it is in virtue of the primitive impetus of the whole that the movement of the parts continues. Something of the whole, therefore, must abide in the parts; and this common element will be evident to us in some way, perhaps by the presence of identical organs in very different organisms. Suppose, for an instant, that the mechanistic explanation is the true one: evolution must then have occurred through a series of accidents added to one another, each new accident being preserved by selection if it is advantageous to that sum of former advantageous accidents which the present form of the living being represents. What likelihood is there that, by two entirely different scries of accidents being added together, two entirely different evolutions will arrive at similar results? The more two lines of evo- lution diverge, the less probability is there that accidental outer influences or accidental inner variations bring about the construction of the same apparatus upon them, es- pecially if there, was no trace of this apparatus at the moment of divergence. But such similarity of the two products would be natural, on the contrary, on a hypothecs like ours: even in the latest channel there would be some- thing of the impulsion received at the source. Pure mechanism, then, would be Tefittable, aiid finalily, in the special sense in which we understand it, would be demon- strable in a certain aspect, if it could be proved that life may manufacture the like apparatus, by unlike means, on di- vergent lines of evolution; and the strength of the proof
Ill THE QUEST OF A CRITERION 55
toould be proportional both to the divergency between the lines of evolution thus chosen and to the complexUy of the similar structures found in tliem.
It will be said that resemblance of structure is due to Bamenesa of the general conditions in which Hfe has evolved, and that these permanent outer conditions may have imposed the same direction on the forces constructing 1 this or that apparatus, in spite of the diversity of transient I outer influences and accidental inner changes. We are not, of course, blind to the role which the concept of adaptation plays in the science of to-day. Biologists cer- tainly do not all make the same use of it. Some think ^the outer conditions capable of causing change in organ- jsms in a direct manner, in a definite direction, through physico-chemical alterations induced by them in the liv- ing substance ; such is the hypothesis of Eimer, for example. Others, more faithful to the spirit of Darwinism, believe the influence of conditions works i-ndirectly only, through
t favoring, in the struggle for life, those representatives of a epecies which the chance of birth has best adapted to the envirormient. In other words, some attribute a positive influence to outer conditions, and say that they actually give rise to variations, while the others say these conditions have only a negative influence and merely eliminate varia- tions. But, in both cases, the outer conditions are sup- posed to bring about a precise adjustment of the organism kto its circumstances. Both parties, then, will attempt to explain mechanically, by adaptation to similar condi- tions, the similarities of structure which wc think are the strongest argument against mechanism. So we must at once indicate in a general way, before passing to the detail, _ why explanations from "adaptation" seem to us insufficient. Let us first remark that, of the two hypotheses just l^escribed, the latter is the only one which is not equivocal.
56 Creative Evolution
The Darwinmn idea of adaptation by automatic eUroioa- tion of the unadapted is a simple and clear idea. But, just because it attributes to the outer cause which con- trols evolution a merely negative influence, it has great difficulty in accounting for the progressive and, so to say, rectilinear development of complex apparatus such as we are about to examine. How much greater will this diffi- culty be in the case of the similar structure of two extremely complex organs on two entirely different lines of evolution! An accidental variation, however minute, implies the working of a great number of small physical and chemical causes. An accumulation of accidental variations, such as would be necessary to produce a complex structure, requires therefore the concurrence of an almost mfinite number of infinitesimal causes. Why should these causes, entirely accidental, recur the same, and in the same order, at different points of space and time? No one will hold that this is the case, and the Darwinian himself will probably merely maintain that identical effects may arise from different causes, that more than one road leads to the same spot. But let us not be fooled by a metaphor. The place reached does not give the form of the road that leads there; while an organic structure is just the accumulation of those small differences which evolution has had to go through in order to achieve it. The struggle for life and natural selection can be of no use to us in solving this part of the problem, for we are not concerned here with what has perished, we have to do only with what has survived. Now, we see that identical structures have been formed on independent lines of evolution by a gradual accumulation of effects. How can accidental causes, occurring in an accidental order, be supposed to have repeatedly come to the same result, the causes being i finitely numerous and the effect infinitely complicated?
The Quest of a Criterion
H The principle of mechanism is that "the same causes produce the same effects." This principle, of course, does not always imp)y that the same effects must have the same causes; but it does involve this consequence in the particu- lar case in which the causes remain visible in the effect that they produce and are indeed its constitutive elements. That two walkers starting from different points and wan- dering at random should finally meet, is no great wonder. But that, throughout their walk, they should describe
I two identical curves exactly superposable on each other, is altogether unlikely. The improbability will be the greater, the more complicated the routes; and it will become impossibility, if the zigzags are infinitely com- plicated. Now, what is this complexity of zigzags as compared with that of an organ in which thousands of different cells, each being itself a kind of organism, are arranged in a definite order? Let us turn, then, to the other hypothesis, and see how
tit would solve the problem. Adaptation, it says, is not merely elimination of the unadapted; it is due to the posi- tive influence of outer conditions that have molded the organism on their own form. This time, similarity of effects will be explained by similarity of cause. We shall remain, apparently, in pure mechanism. But if we look closely, we shall see that the explanation is merely verbal, that we are again the dupes of words, and that the trick of the solution consists in taking the term "adaptation" in two entirely different senses at the same time.
If I pour into the same glass, by turns, water and wine,
the two hqutds will take the same form, and the sameness
in form will be due to the sameness In adaptation of content
to container. Adaptation, here, really means mechanical
adjustment. The reason is that the form to which the
matter has adapted itself was there, ready-made, and
has forced its own ghape on the matter. But, in the adaptation of an organism to the circumstances it has to five in, where is the pre-existing form awaiting its matter? The circumstances are not a mold into which life is inserted and whose form life adopts: this is indeed to be fooled by a metaphor. There is no form yet, and the life must create a form for itself, suited to the circumstances which are made for it. It will have to make the best of these circumstances, neutralize their inconveniences and utilize their advantages^in short, respond to outer actions by building up a machine which has no resemblance to them. Such adapting is not repeating, but replying, — an entirely different thing. If there is still adaptation, it will be in the sense in which one may say of the solution of a problem of geometry, for example, that it ia adapted to the con- ditions. I grant indeed that adaptation so understood explains why different evolutionary processes result in similar forms: the same problem, of course, calls for the same solution. But it is necessary then to introduce, as for the solution of a problem of geometry, an intelligent activity, or at least a cause which behaves in the same way. This is to bring in finality again, and a finality this time more than ever charged with anthropomorphic elements. In a word, if the adaptation is passive, if it is mere repetition in the relief of what the conditions give in the mold, it will build up nothing that one tries to make it build ; and if it is active, capable of responding by a calculated solu- tion to the problem which is set out in the conditions, that is going further than we do — too far, indeed, in our opinion— in the direction we indicated in the beginning. But the truth is that there is a surreptitious passing from one of these two meanings to the other, a flight for refuge to the first whenever one is about to be caught injlagranie delicto of finaUsm by employing the second. It is really
The Quest of a Criterion
the second which serves the usual practice of science, but it is the first that generally provides its philosophy. In any particular case one talks as if the process of adaptation were an effort of the organism to build up a machine capable of turning external circumstances to the best possible account: then one speaks of adaptation in general as if it were the very impress of circumstances, passively received by an indifferent matter.