It may be claimed that considerations of utility are out of place here; that the eye is not made to sec, but that we see because we have eyes; that the organ is what it is, and " utility^' is a word by which we designate the functional effects of the structure. But when I say that the eye "makes use of" light, I do not merely mean that the eye is capable of seeing; I allude to the very precise relations that exist between this organ and the apparatus of lo- comotion. The retina of vertebrates is prolonged in an optic nerve, which, again, is continued by cerebral centres connected with motor mechanisms. Our eye makes use of light in that it enables us to utilize, by movements of reaction, the objects that we see to be advantageous, and to avoid those which we see to be injurious. Now, of course, as bght may have produced a pigment-spot by physical means, so it can physially determine the move- ments of certain organisms; ciliated Infusoria, for in- stance, react to light. But no one would hold that the influence of light has physically caused the formation of a nervous system, of a muscular system, of an osseous eystem, all things which are continuous with the apparatus of vision in vertebrate animals. The truth is, when one
nd, still more^^^l
epeaks of the gradual formation of the eye, and, i when one takes into account all that is inseparably con- nected tt-ith it, one brings in something entirely different from the direct action of light. One implicitly attributes to organized matter a certain capacity sui generis, the mysterious power of building up very complicated machines to utilize the simple excitation that it undergoes.
But this is just what is claimed to be unnecessary. Physics and chemistry are said to give us the key to every- thing. Eimer's great work is instructive in this respect. It is well known what persevering effort this biologist has devoted to demonstrating that transformation is brought about by the inSuence of the external on the in- ternal, continuously exerted in the same direction, and not, as Darwin held, by accidental variations. His theory rests on observations of the highe.st interest, qf which the starting-point was the study of the course followed by the color variation of the skin in certain Uzards. Before this, the already old experiments of Dorfmeister had shown that the same chrysalis, according as it was sub- mitted to cold or heat, gave rise to very different butter- flies, which had long been regarded as independent species, Vanessa levana and Vanessa prorsa: an intermediate tem- perature produces an intermediate form. We might class with these facts the important transformations observed in a little crustacean, Artemia sa/ina, when the salt of the water it lives in is increased or diminished,' In these various experiments the external agent seems to act as a cause of transformation. But what does the word "cause"
It seems, from later observations, that the tmiiaFormatioD of Artemia is a more complex phenomenon than was first BUpposcd. See on this eubject Sunter ami Heymons, " Die Variatjon bei Artemia Salina" (Anhang tti den Abhandlungen der k. preuttUchen Akad. dtr tfuvffnMAn/Iffn, 1902).
mean here? Without undertaking an exhaustive analysis of the idea of causality, we will merely remark that three very different meanings of this term are commonly con- fused. A cause may act by im-peUiTig, releasing, or un- winding. The billiard-ball, that strikes another, deter- mines its movement by impelling. The spark that explodes the powder acts by releasing. The gradual relaxing of the spring, that makes the phonograph turn, unwinds the melody inscribed on the cylinder: if the melody which is played be the effect, and the relaxing of the spring the cause, we must say that the cause acts by unwinding. What distinguishes these three cases from each other is the greater or less solidarity between the cause and the effect. In the first, the quantity and quality of the effect vary with the quantity and quality of the cause. In the second, neither quality nor quantity of the effect varies with quality and quantity of the cause: the effect is invariable. In the third, the quantity of the effect depends on the quantity of the cause, but the cause does not influence the quality of the effect: the longer the cylinder turns by the action of the spring, the more of the melody I shall hear, but the nature of the melody, or of the part heard, does not depend on the action of the spring. Only in the firat case, really, does cause explain effect ; in the others the effect is more or less given in advance, and the antecedent invoked is — in different degrees, of course — its occasion rather than its cause. Now, in saying that the saltness of the water ia the cause of the transformations of Artemia, or that the degree of temperature determines the color and marks of the wings which a certain chrysalis will assume on be- coming a butterfly, ia the word "cause" used in the first sense? Obviously not : causality has here an intermediary sense between those of unwinding and releasing. Such, indeed, seems to be Elmer's own meaning when he speaks
74 CREATIVE EVOLUTION iohap;
of the "kaleidoscopic" character of the variation,' or when he says that the variation of organized matter works in a definite way, just as inorganic matter crj-stalhzes in definite directions.' And it may be granted, perhaps, that the process is a merely physical and chemical one in the case of the color-changes of the skin. But if this sort of explanation ia extended to the case of the gradual forma- tion of the eye of the vertebrate, for instance, it must be supposed that the phyaico-chemistry of living bodies is such that the influence of Ught has caused the organism to construct a progressive series of visual apparatus, all extremely complex, yet all capable of seeing, and of seeing better and better." What more could the most confirmed finalist say, in order to mark out so exceptional a physico chemistry? And will not the position of a mchanistic philosophy become still more difficult, when it is pointed out to it that the egg of a mollusc cannot have the same chemical composition as that of a vertebrate, that the organic substance which evolved toward the first of these two forms could not have been chemically identical with that of the substance which went in the other direction, and that, nevertheless, under the influence of light, the same organ has been constructed in the one case as in the other?
The more we reflect upon it, the more we shall see that
this production of the same effect by two different ac-
cumulations of an enormous number of small causes is
contrary to the principles of mechanistic philosophy.
We have concentrated the full force of our discussion upon
an example drawn from phylogenesis. But ontogenesis
would have furnished us with facts no less cogent. Every
' Eime-, Orikoijenesw der Schmaterlinge, Leipiig, 1897, p. 24. Ct Die BrUttehuny der Arlen, p. 63.
r, I>i4 EttUUKung der Arlen, Jena, 1888, p. 25, • Ibid. pp. IQS ff.
moment, right before our eyes, nature arrives at identical results, in sometimes neighboring species, by entirely different embryogenic processes. Observations of "heter- oblastia" have multiplied in late years,' and it has been necessary to reject the almost classical theory of the epecificity of embryonic gills. Still keeping to our compari- 6on between the eye of vertebrates and that of molluscs, we may point out that the retina of the vertebrate is produced by an expansion in the rudimentary brain of the young embryo. It is a regular nervous centre which has moved toward the periphery. In the mollusc, on the contrary, the retina is derived from the ectoderm directly, and not indirectly by means of the embryonic encephalon. Quite different, therefore, are the evolutionary processes which lead, in man and in the Pecten, to the development of a like retina. But. without going so far as to compare two organisms so distant from each other, we might reach the same conclusion simply by looking at certain very curious facts of regL-neration in one and the same organism. If the crj'stalline lens of a Triton be removed, it is re- generated by the iris." Now, the original lens was built out of the ectoderm, while the iris is of mesodermic ori^n. What is more, in the SalamandTa macutata, if the lens be removed and the iris left, the regeneration of the lens takes place at the upper part of the iris; but if this upper part of the iris itself be taken away, the regeneration takes place in the inner or retinal layer of the remaining region.'
' Sftlensky, 'Heteroblastie" (Proc. of the Fourth Intematiorud Con- gntt a/ Zoology, London, 1899, pp. 111-118). Salensky ha.s coined this word to designate the canes in which organa that are equivalent, but of different embryological origin, are formed at the same points ID aolmata relalixl to each other.
' Wolff, "Die Regeneration der Urodelenlinse " {Arch. /. Entwick- ^migmechanik. i., 1895, pp. 380 St.).
* Fischel, "Ulxr die Regeneration der Linse" (Ana/. Ameiger, xiv,, 1898, pp. 373-380).
76 Creative Evolution
Thus, parts differently situated, differently constituted,
meant normally for different functions, are capable of
performing the same duties and even of manufacturing,
when necessary, the same pieces of the machine. Here
we have, indeed, the same effect obtained by different
combinations of causes.
Whether we will or no, we must appeal to some inner directing principle in order to account for this convergence of effects. Such convergence does not appear possible in the Darwinian, and especially the neo-DarwinJan, theory of insensible accidental variations, nor in the hypothesis of sudden accidental variations, nor even in the theory that assigns definite directions to the evolution of the various organs by a kind of mechanical composition of the external with the internal forces. So we come to the only one of the present forms of evolution which re- mains for us to mention, viz., neo-Lamarckism.
It is well known that Lamarck attributed to the living being the power of varying by use or disuse of its oi'gans, and also of passing on the variation so acquired to its descendants. A certain number of biologists hold a doctrine of this kind to-day. The variation that results in a new species is not, they believe, merely an accidental variation inherent in the germ itself, nor is it governed by a determinism sui generis which develops definite characters in a definite direction, apart from every consideration of utility. It springs from the very effort o^the living being to adapt itself to the circumstances of its existence. The effort may indeed be only the mechanical exercise of cer- tun organs, mechanically elicited by the pressure of ex- ternal circumstances. But it may also imply consciousness and will, and it is in this sense that it appears to be under- stood by one of the most eminent representatives of the
doctrine, the American naturalist Cope.' Neo-Laraarcldsm is therefore, of all the later forms of evolutionism, the only one capable of admitting an internal and psychological principle of development, although it is not bound to do go. And it ia also the only evolutionism that seems to us to account for the building up of identical complex organs on independent lines of development. For it is quite conceivable that the same effort to turn the same circumstances to good account might have the same result, especially if the problem put by the circumstances is such as to admit of only one solution. But the question re- mains, whether the term "effort" must not then be taken iu a deeper sense, a sense even more psychological than any neo-Lamarckian supposes.
For a mere variation of size is one thing, and a change of form is another. That an organ can be strengthened and grow by exercise, nobody will deny. But it is a loag way from that to the progressive development of an eye hke that of the molluscs and of the vertebrates. If this development be ascribed to the influence of light, long continued but passively received, we fall back on the theory we have just criticized. If, on the other hand, an internal activity ia appealed to, then it naust be something quite different from what we usually call an effort, for never has an effort been known to produce the slightest com- pUcation of an organ, and yet an enormous number of complications, all admirably coordinated, have been necessary to pass from the pigment-spot of the Infusorian to the eye of the vertebrate. But, even if we accept this notion of the evolutionary process in the case of animals, how can we apply it to plants? Here, variations of form do not seem to imply, nor always to lead to, functional
<Oope, TheOrigmot the FiUett. 1^7] The PHmary Factors of Organic Svohdim, 11