Part 23 (1/2)
[108] See especially Darwin: ”The Variation of Animals and Plants under Domestication”; Haeckel: ”Naturliche Schopfungsgeschichte,” 8th ed., 1889, p. 179 _et seq._
[109] ”Die Entstehung der Arten auf Grund von Vererben erworbener Eigenschaften,” p. 204 _et seq._
[110] Ibid. p. 190 _et seq._
[111] ”Entstehung der Arten,” p. 15.
CHAPTER II
INTELLIGENCE AND ”END”
It is interesting to notice the opinions of different scientists and philosophers as to the extent to which reason is diffused in the universe, where the point lies at which the boundary line is to be drawn between reason and an automatism of instinct or organic action, or whether any such point can be found at all, whether reason, at least as consciousness and will, is not inherent in all life, or at least in all animal life, or whether it is not, indeed, to be regarded as the cause of motion even outside life, in the inorganic as well as the organic.
There is no need to remind ourselves of the philosophic conception of the World as Will, the Philosophy of the Unconscious, or the Theory of Monads. The theories that specialists in physical science have arrived at, through the results of wide-reaching investigations in their own peculiar branch, are as various as those of philosophers. Darwin carefully avoids drawing any distinct limit-line between reason and instinct, but remarks that ”A little dose of judgment or reason, as Pierre Huber expresses it, often comes into play, even with animals low in the scale of nature.”[112] Haeckel says: ”Unbia.s.sed comparison and unprejudiced test and observation place it beyond doubt that so-called 'instinct' is nothing else than a sum of soul-activities which, originally acquired by adaptation, have been fixed by habit and carried down from generation to generation by inheritance. Originally performed with consciousness and reflection, many instinctive actions of the animals have become, in the course of time, unconscious, exactly as is the case with the habitual activities of human reason. These, too, may, with like justice, be looked upon as the workings of innate instinct, as, indeed, the impulse to self-preservation, maternal love, and the social instinct often are regarded. Again, instinct is neither distinctively an attribute of the brain of the animal, nor is the reason an especial endowment of human beings. On the contrary, an impartial doctrine of soul recognizes a long, long, descending scale of gradual evolution in the life of the soul, which leads from higher to lower human beings, from more perfect to more imperfect animals, step by step, down to those forms whose simple nerve-ganglion furnishes the starting-point of all the cell-less brain-forms of this scale.”[113] The lecture in which this pa.s.sage occurs not only argues further that the soul is composed of soul-activities as the brain is composed of cells, but finds in all living cells, ”all protoplasm, the first element of all soul life, sensation in the simple forms of pain and pleasure, movement in the simple forms of attraction and repulsion. Only the degrees of development and combination of soul are different in different beings.”
Du Prel, impressed with the evolution of order from disorder in the heavens as on the earth, ascribes this to universal sensation as a fundamental quality of all matter, which makes it continually tend towards a state of equilibrium in which collision is reduced to a minimum.[114] Some biologists ascribe sensation, or consciousness, to animal life alone; some ascribe consciousness to such animals only as possess a nervous system; some philosophers make a distinction between sensation, consciousness, and self-consciousness, as shown in the scale of animal life; some, again, approaching the problem from another side, lay emphasis on the difference between automatic and organic action, instinct, ”blind impulse,” and will. Carneri, as we have seen,[115]
holds that even the action of an animal so high in the scale as the b.u.t.terfly may be pure automatism, its fluttering when impaled merely the motion of a continued attempt at flight.
These differences in opinion seem to depend, in great measure, upon the end of the scale of being chosen as the starting-point in the development of theory. If we begin with man and a.s.sume intelligence to be the cause of design,--of the purposeful, the self-preserving,--in his action, we shall be likely to infer intelligence as the cause of self-preserving function in all animals, and we shall find great difficulty in drawing any distinct line between intelligence and automatism. If we are not students of inorganic nature, the evolution to be found also in it, up to the attainment of preservative forms of motion, may escape our observation, preoccupation with man and the self- or rather human-interested bias of observation blinding us to it; but if we carry our considerations, in an unprejudiced spirit, on beyond the province of life, we may, like Du Prel and others, arrive at a theory of intelligence as a universal property of matter. On the other hand, if we begin with inorganic matter and a.s.sume automatism to be the cause of its motion, we are likely, ascending the scale of organic existence, to interpret much of its function as due to material action and reaction, and may again, from this side, find so great difficulty in drawing the line where intelligence begins, that we may fall, as Carneri has done, into the opposite extreme to that last noticed, and interpret nearly all animal action as unintelligent or even insentient.
Let us look at the dilemma a little more closely. Might it not seem, from one point of view, as if the harmonious movements of the stars, by which they avoid their own destruction, must be referred to desire and will to avoid it? If all systems of material parts, without exception or distinction, tend, as Fechner, Du Prel, and Petzoldt a.s.sert, towards harmony of the parts such that the motion of these parts will become self-preservative, does it not seem logically necessary to a.s.sume that this self-preservation, arising in inorganic matter in the same manner as in organic matter, must be due to the same causes as those to which we ascribe action towards an end, action that involves self-preservation, in the broadest sense of the word, in man? May not the heavenly bodies, learning from experience in some way, as man does, gradually come to choose, though still in accordance with natural laws (as man also invariably chooses) that orbit which preserves them from collision? True, they must finally suffer destruction, but so, also, must the human individual, and the race of human beings. The difference of evolution and dissolution in the two cases is only one of time. Among different species of nervously organized beings, the duration of life also differs. Or, if we deny the existence of intelligence in inorganic nature, can we, at least, descending the scale of organic being, find any point of which we can say, ”Here intelligence ends and automatism begins”? Shall we deny the existence of intelligence in plants, and if so, how shall we find that dividing line between the plant and animal kingdoms which the advancement of science in many directions is rendering, not more distinct, but less and less so? G. Th. Schneider says, in his book on ”The Human Will”: ”The movements of touch and locomotion in the search for food are the first movements in which the specific animal-life may be recognized. In no plant is the groping caused by hunger to be observed.”[116] But is this true? The insectivorous plants, for instance, open their leaves when their prey is digested, waiting for fresh prey; and they close them again when prey has again entered, thus practically grasping their victim and holding him fast. Although the nature of the plant prevents its moving from the spot where it grows, are these movements less a search for and capture of food than those of the animal? To say that the closing of the leaves depends upon the beginning of some chemical process in the plant furnishes us with no mark of distinction between the two, for it is equally true that chemical processes underlie animal motion; and to object that the reopening of the leaves is the result of the completion of a.s.similation gives us, also, no distinctive mark, since the animal's search for food is likewise the result of hunger and so connected with a particular state of the digestive organs. The action of insectivorous plants draws our attention because the process of a.s.similation involved so resembles animal digestion; but, as a point of fact, the opening of petals to receive the air and sun is as much a search for food as the opening of leaves to receive insect prey.
Schneider adds to the pa.s.sage above quoted, ”A further difference between psychical and physiological movements is this, that the latter always remain the same, however the excitation changes, while the former have, now the character of attraction, now that of repulsion.” It may be questioned whether this difference either can be demonstrated to be a distinctive mark. We have only to go into a dark cellar where the potatoes have begun to sprout, in order to see how plants that ordinarily grow upward will take every curve and angle in order to reach towards the light of some distant window. And if we turn one of the tubers about, we may watch the pallid sprout again turn to grow towards the far-away sunlight. Thomas A. Knight relates experiments in which plants of the Virginia creeper (_Ampelopsis quinquefolia_) were removed from one side of the house to the other, being, in each case, screened from perpendicular rays of the sun, and records that, in all cases, the tendrils turned in a few hours in a direction pointing to the centre of the house. One plant after being thus experimented with, was ”removed to the centre of the house and fully exposed to the perpendicular light of the sun; and a piece of dark-colored paper was placed upon one side of it, just within reach of its tendrils; and to this substance they soon appeared to be strongly attracted. The paper was then placed upon the opposite side, under similar circ.u.mstances, and a piece of plate gla.s.s was subst.i.tuted; but to this substance the tendrils did not indicate any disposition to approach. The position of the gla.s.s was then changed, and care was taken to adjust its surface to the varying position of the sun, so that the light reflected might continue to strike the tendrils; which then receded from the gla.s.s, and appeared to be strongly repulsed by it.”[117] Darwin writes of the insectivorous _Drosera rotundifolia_: ”If young and active leaves are selected, inorganic particles not larger than the head of a small pin, placed on the central glands, sometimes cause the outer tentacles to bend inwards. But this follows much more surely and quickly, if the object contains nitrogenous matter which can be dissolved by the secretion. On one occasion, I observed the following unusual circ.u.mstance. Small bits of raw meat (which acts more energetically than any other substance), of paper, dried moss, and of the quill of a pen, were placed on several leaves, and they were all embraced equally well in about two hours. On other occasions the above-named substances, or more commonly particles of gla.s.s, coal-cinder (taken from the fire), stone, gold-leaf, dried gra.s.s, cork, blotting paper, cotton-wool, and hair rolled into little b.a.l.l.s, were used, and these substances, though they were sometimes well embraced, often caused no movement whatever in the outer tentacles, or an extremely slight and slow movement. Yet these same leaves were proved to be in an active condition, as they were excited to movement by substances yielding nitrogenous matter, such as bits of raw or roast meat, the yolk or white of boiled eggs, fragments of insects of all orders, spiders, etc. I will give only two instances.
”Minute flies were placed on the discs of several leaves, and on others b.a.l.l.s of paper, bits of moss and quill of about the same size as the flies, and the latter were well embraced in a few hours; whereas after twenty-five hours only a very few tentacles were inflected over the other objects. The bits of paper, moss, and quill were then removed from these leaves, and bits of raw meat placed on them; and now all the tentacles were soon energetically inflected.
”Again, particles of coal-cinder (weighing rather more than the flies used in the last experiment) were placed on the centres of three leaves: after an interval of nineteen hours, one of the particles was tolerably well embraced; a second by a very few tentacles; and a third by none. I then removed the particles from the two latter leaves, and put on them recently killed flies. These were fairly well embraced in seven and one-half hours, and thoroughly after twenty and one-half hours; the tentacles remaining inflected for many subsequent days. On the other hand, the one leaf which had in the course of nineteen hours embraced the bit of cinder moderately well, and to which no fly was given, after an additional thirty-three hours (_i.e._ in fifty-two hours from the time when the cinder was put on) was completely reexpanded and ready to act again.”[118]
From these and many other experiments Darwin concludes that inorganic and some organic substances not attacked by the secretion of the leaf act much less quickly and efficiently than organic substances yielding soluble matter, which is absorbed.
He also writes of the curvature of radicles which come in contact with obstacles at right angles:--
”The first and most obvious explanation of the curvature is that it results merely from the mechanical resistance to the growth in its original direction. Nevertheless, this explanation did not seem to us satisfactory. The radicles did not present the appearance of having been subjected to a sufficient pressure to account for their curvature. Sachs has shown that the growing part is more rigid than the part immediately above, which has ceased to grow, so that the latter might have been expected to yield and become curved as soon as the apex encountered an unyielding object; whereas it was the stiff, growing part which became curved. Moreover, an object which yields with the greatest ease will deflect a radicle: thus, as we have seen, when the apex of the radicle of the bean encountered the polished surface of extremely thin tin-foil on soft sand, no impression was left on it, yet the radicle became deflected at right angles. A second explanation occurred to us, namely, that even the gentlest pressure might check the growth of the apex, and in this case growth could continue only on one side, and thus the radicle would a.s.sume a rectangular form; but this view leaves wholly unexplained the curvature of the upper part, extending for a length of 8-10 mm.
”We were therefore led to suspect that the apex was sensitive to contact, and that the effect was transmitted from it to the upper part of the radicle, which was excited to bend away from the touching object.
As a little loop of fine thread, hung on a tendril or on the petiole of a leaf-climbing plant, causes it to bend, we thought that any hard object affixed to the tip of a radicle, freely suspended and growing in damp air, might cause it to bend if it were sensitive, and yet would not offer any mechanical resistance to its growth.... Sachs discovered that the radicle a little above the apex is sensitive and bends like a tendril _towards_ the touching object. But when one side of the apex is pressed by any object, the growing part bends _away_ from the object.”[119]
Acting on this idea, Darwin found, in many experiments, that the radicles of plants freely suspended in bottles, when brought into contact with the most yielding substances, bits of paper, etc., were deflected, in a very few hours, from their original course, and often at right angles to this. He says, further:--
”As the apex of a radicle in penetrating the ground must be pressed on all sides, we wished to learn whether it could distinguish between harder, or more resisting, and softer substances. A square of sanded paper almost as stiff as card, and a square of extremely thin paper (too thin for writing on) of exactly the same size (about one-twentieth of an inch), were fixed with sh.e.l.lac on opposite sides of the apices of twelve suspended radicles.... In eight out of the twelve cases, there could be no doubt that the radicle was deflected from the side to which the card-like paper was attached and towards the opposite side bearing the very thin paper.
”This occurred, in some instances, in nine hours, but in others not until twenty-four hours had elapsed. Moreover, some of the four failures can hardly be considered as really failures: thus, in one of them in which the radicle remained quite straight, the square of thin paper was found, when both were removed from the apex, to have been so thickly coated with sh.e.l.lac that it was almost as stiff as the card; in the second case, the radicle was bent upward into a semicircle, but the deflection was not directly from the side bearing the card, and this was explained by the two squares having become cemented laterally together, forming a sort of stiff gable from which the radicle was deflected; in the third case, the square of card had been fixed by mistake in front, and though there was deflection, this might have been due to Sachs's curvature; in the fourth case alone, no reason could be a.s.signed why the radicle had not been at all deflected.”
Darwin found, moreover, by experiment, that, when the tip of a radicle is burnt or cut, ”it transmits an influence to the upper adjoining part, causing it to bend away from the affected side.” This deflection resembles, in a very striking manner, the avoidance of sources of injury and pain on the part of animals.
And at the end of his book on the Movements of Plants, which contains very many other experiments bearing on the question of sensitivity in plants, the author writes, ”It is hardly an exaggeration to say that the tip of the radicle thus endowed, and having the power of directing the movements of the adjoining parts, acts like the brain of one of the lower animals.”
It is true that the plant does not react with the rapidity which characterizes the animal; Darwin found that radicles are not sensitive to temporary contact, but only to long, though to slight pressure. It is also true that the physical basis of the movement is more simple, and so more easily traceable in the plant than in the animal organism; yet why lay such especial stress upon this side of plant-life, since it is acknowledged that the physical basis is by no means peculiar to it, but that, on the contrary, all life-processes, in the animal as well as in the plant, have their physical side, although greater complexity of organization may make this more difficult to follow in the one case than in the other?
But we may begin at the other end of the scale and examine the facts presented from the opposite point of view. The physicist demonstrates that force is indestructible; that is, that the sum of the motion and resistance to motion residing in indestructible matter is also imperishable, that all present motion must be regarded as the resultant of previous conditions of motion and resistance, as far back as we may go, until we reach some a.s.sumed primal state (which is only a.s.sumed and cannot be proved to have existed) in which the matter composing the universe is supposed to have been at complete rest; and that every resultant bears relations to its component factors of force that are constant, every component finding its full value in the resultant. What evidence has the present state of our solar system and the other systems of heavenly bodies revealed to us by the telescope to offer us in proof of their consciousness or sentience? How are the whirl and concentration of nebular mists, the crash and collision of elemental bodies, from which, by simple action and reaction, after ages of disharmony, only a comparative harmony is arrived at as inevitable result, evidence of aim, intention, will, consciousness, in the matter subject to this evolution?
Do we find anything here except blind law? The movements of plants, often directly favorable to self-preservation, may be explained by the arrangement of the cells and their chemical action. Or, if sentience must be a.s.sumed to be the cause of movement attaining ends of self-preservation in plants, how are we to account for organic and instinctive action in animals? How is it, for instance, that the new-born infant sucks, and the chicken but a few hours old, even though it has been hatched in an incubator apart from its kind, picks at the food strewn before it, aiming, too, with considerable precision?[120]