But it is easier to define the method than to apply it. The complete interpretation of the evolution movement in the past, as we conceive it, would be possible only if the history of the deveJopment of the organized world were entirely known. Such is far from being the case. The genealogies proposed for the different species are generally questionable. They varj- with their authors, with the theoretic views inspiring them, and raise dis- cussions to which the present state of science does not admit of a final settlement. But a comparison of the different solutions shows that the controversy bears less on the main lines of the movement than on matters of detail ; and so, by following the main lines as closely as possible, we shall be sm-e of not going astray. Moreover, they alone arc important to us; for we do not aim, like the naturaUst, at finding the order of succession of different species, but only at defining the principal directions of their evolution. And not all of these directions have the same interest for ub; what concerns us particularly is the path that leads to man. We shall therefore not lose sight of the fact, in following one direction and another, that our main business is to determine the relation of man to the animal kingdom, and the place of the animal kingdom itself in the organized world as a whole.
To begin with the second point, let us say that no definite
characteristic distinguishes the plant from the animal.
Attempts to define the two kingdoms strictly have always
106 Creative Evolution
come to naught. There is not a single property of vege- table life that is not found, in some degree, in certain ani- mals; not a single characteristic feature of the animal that has not been seen in certain species or at certain moments in the vegetable world. Naturally, therefore, biologists enamored of clean-cut concepts have regarded the distinction between the two kingdoms as artificial. They would be right, if definition in this case must be made, as in the mathematical and physical sciences, according to certain statical attributes which belong to the object defined and are not found in any other. Very different, in our opinion, is the kind of definition which befits the sciences of life. There is no manifestation of life which does not contain, in a rudimentary state — either latent or potential, — the essential characters of most other mani- festations. The difference is in the proportions. But this very difference of proportion will suffice to define the group, if we can establish that it is not accidental, and that the group as it evolves, tends more and more to emphasize these particular characters. In a word, the group must not be defined by Ike possession of certain ckaracters, but by its tendency to emphasize them. From this point of view, taking tendencies rather than states into account, we find that vegetables and animals may be precisely defined and distinguished, and that they correspond to two divergent developments of life.
This divergence is shown, first, in the method of ali- mentation. We know that the vegetable derives directly from the air and water and soil the elements necessary to maintain life, especially carbon and nitrogen, which it takes in mineral form. The animal, on the contrary, cannot assimilate these elements unless they have already been fixed for it in organic substances by plants, or by animals which directly or indirectly owe them to plants;
80 that ultimately the vegetable nourishes the animal. True, this law allows of many exceptions among vegetables. We do not hesitate to class amongst vegetables the Drosera, the Dionaea, the Pinguieula, which are insectivorous plants. On the other hand, the fungi, which occupy so considerable a place in the vegetable world, feed like ani- mals: whether they are ferments, saprophytes or parasites, it is to already formed organic substances that they owe their nourishment. It is therefore impossible to draw from this difference any static definition such as would auto- matically settle in any particular case the question whether we are dealing with a plant or an animal. But the difference may provide the beginning of a dynamic definition of the two kingdoms, in that it marks the two divergent di- rections in which vegetables and animals have taken their course. It is a remarkable fact that the fungi, which nature has spread all over the earth in such extraordinary profusion, have not been able to evolve. Organically they do not rise above tissues which, in the higher vegetables, are formed in the embryonic sac of the ovary, and precede the germinative development of the new individual.' They might be called the abortive children of the vege- table world. Their different species are like so many blind alleys, as if, by renouncing the mode of alimentation custom- ary amongst vegetables, they had been brought to a stand- still on the highway of vegetable evolution. As to the Drosera, the Dionaea, and insectivorous plants in general, they are fed by their roots, hke other plants; they too fix, by their green parts, the carbon of the carbonic acid in the atmosphere. Their faculty of capturing, absorbing and digesting insects must have arisen late, in quite exceptional cases where the soil was too poor to furnish sufficient nour- ishment. In a general way, then, if we attach less im- De SapoTta u)d Marion, L'Evolution dei eryplogamet, ISSl, p. 37.
portance to the presence of special characters than to their tendency to develop, and if we regard as essential that tendency along which evolution has been able to continue indefinitely, we may say that vegetables are distinguished from animals by their power of creating organic matter out of mineral elements which they draw directly from the air and earth and water. But now we come to another difference, deeper than this, though not unconnected with it. The animal, being unable to fix directly the carbon and nitrogen which are everywhere to be found, has to seek for its nourishment vegetables which have already fixed these elements, or animals which have taken them from the vegetable kingdom. So the animal must be able to move. From the amoeba, which thrusts out its pseudopodia at random to seize the organic matter scattered in a drop of water, up to the higher animals which have sease-organs with which to recognize their prey, locomotor organs to go and seize it, and a ncn'ous system to coordinate their movements with their sen- sations, animal life is characterized, in its general direction, by mobility in space. In its most rudimentary form, the animal is a tiny mass of protoplasm enveloped at most in a thin albuminous pellicle which allows full freedom for change of shape and movement. The vegetable cell, on the contrary, is surrounded by a membrane of cellu- lose, which condemns it to immobility. And, from the bottom to the top of the vegetable kingdom, there are the same habits growing more and more sedentary, the plant having no need to move, and finding around it, in the air and water and soil in which it is placed, the mineral ele- ments it can appropriate directly. It is true that phe- nomena of movement are seen in plants. Darwin has written a well-known work on the movements of climbing plants. He studied also the contrivances of certain in-
sectivorous plants, such as the Drosera and the Dionaea, to seize their prey. The leaf-movements of the acacia, the seiaitive plant, etc., are well known. Moreover, the circulation of the vegetable protoplasm within its sheath bears witness to its relationship to the protoplasm of animals, whilst in a large number of animal species (generally parasites) phenomena of fixation, analogous to those of vegetables, can be observed." Here, again, it would be a mistake to claim that fixity and mobility are the two characters which enable us to decide, by simple inspection alone, whether we have before us a plant or an animal. But fixity, in the animal, generally seems Uke a torpor into which the species has fallen, a refusal to evolve further in a certain direction; it is closely akin to parasitism and is accompanied by features that recall those of vegetable life. On the other hand, the move- ments of vegetables have neither the frequency nor the variety of those of animals. Generally, they involve only part of the organism and scarcely ever extend to the whole. In the exceptional cases in which a vague spontaneity appears in vegetables, it is as if we beheld the accidental awakening of an activity normally asleep. In short, although both mobility and fixity exist in the vegetable as in the animal worid, the balance is clearly in favor of fixity in the one case and of mobility in the other. These two opposite tendencies are so plainly directive of the two evolutions that the two kingdoms might almcMt be defined by them. But fixity and mobility, again, are only super- ficial signs of tendencies that are still deeper.
Between mobility and consciousness there is an obvious
relationship. No doubt, the consciousness of the higher
or;ganism3 seems bound up with certain cerebral arrange-
< On fix&Uon and parasitism in general, see the work of HoussAy, La Forme et la vU, Paris. 1900, pp. 721-807.
ments. The more the nervous system develops, the more numerous and more precise become the movements among which it can choose; the clearer, also, is the consciousness that accompanies them. But neither this mobility nor this choice nor consequently this consciousness involves as a necessary condition the presence of a nervous system; the latter has only canalized in definite directions, and brought up to a higher degree of intensity, a rudimentary and vague activity, diffused throughout the mass of the organized substance. The lower we descend in the ani- mal series, the more the nervous centres are simplified, and the more, too, they separate from each other, till finally the nervous elements disappear, merged iQ the mass of a less differentiated organism. But it is the same with all the other apparatus, with all the other anatomical elements; and it would be as absurd to refuse consciousness to an animal because it has no brain as to declare it in- capable of nourishing itself because it has no stomach. The truth is that the nervous system arises, like the other systems, from a division of labor. It does not create the function, it only brings it to a higher degree of intensity and precision by giving it the double form of reflex and voluntary activity. To accomplish a true refle:: move- ment, a whole mechanism is necessary, set up in the spinal cord or the medulla. To choose voluntarily between several definite courses of action, cerebral centres are necessary, that is, crossways from which paths start, leading to motor mechanisms of diverse form but equal precision. But where nervous elements are not yet canal- ized, still less concentrated into a system, there is some- thing from which, by a kind of splitting, both the reflex and the voluntary will arise, something which has neither the mechanical precision of the former nor the intelli- gent hesitations of the latter, but which, partaking of
both
both it may be infimtesimally, is a reaction simply unde- cided, and therefore vaguely conscious. This amounts to saying that the humblest organism is conscious in pro- portion to its power to move fredy. Is consciousness here, in relation to movement, the effect or the cause? In one sense it is the cause, since it has to direct loco- motion. But in another sense it is the effect, for it is the motor activity that maintains it, and, once this activity disappears, consciousness dies away or rather falls asleep. In crustaceans such as the rMzocephala, which must formerly have shown a more differentiated structure, fixity and parasitism accompany the degeneration and almost complete disappearance of the nervous system. Since, in such a case, the progress of organization must have localized all the conscious activity in nervous centres, we may conjecture that consciousness is even weaker in animals of this kind than in organisms much less differen- tiated, which have never had nervous centres but have remained mobile.
How then could the plant, which is fixed in the earth and finds its food on the spot, have developed in the di- rection of conscious activity? The membrane of cellulose, in which the protoplasm wraps itself up, not only prevents the simplest vegetable organism from moving, but screens it also, in some measure, from those outer stimuli which act on the sensibility of the animal as irritants and prevent it from going to sleep. ' The plant ia therefore unconscious. Here again, however, we must beware of radical distinctions. "Unconscious" and "conscious" are not two labels which can be mechanically fastened, the one on every vegetable cell, the other on all animals. While consciousness sleeps in the animal which has degenerated into a motionless parasite, it probably awakens in the vegetable that has ' Cbpe, op. cU. p. 76.
Creati\-E Evolution
(OHAP.