enim corpus instrumentum: nam membrum unumquodque rei alicujus gratia est, tum vero totum ipsum.) At greater length, p. 633 and 645 of the Berlin quarto edition, and also De incessu animalium, c. 2: “Ἡ φυσις ουδεν ποιει ματην, αλλ᾽ αει, εκ των ενδεχομενων τῃ ουσιᾳ, περι ἑκαστον γενος ζωου το αριστον.” (Natura nihil frustra facit, sed semper ex iis, quæ cuique animalium generis essentiæ contingunt, id quod optimum est.) But he expressly recommends teleology at the end of the books De generatione animalium, and blames Democritus for having denied it, which is just what Bacon, in his prejudice, praises in him. Especially, however, in the “Physica,” ii. 8, p. 198, Aristotle speaks ex professo of final causes, and establishes them as the true principle of the investigation of nature. In fact, every good and regular mind must, in considering organised nature, hit upon teleology, but unless it is determined by the preconceived opinions, by no means either upon physico-theology or upon the anthropo-teleology condemned by Spinoza. With regard to Aristotle generally, I wish further to draw attention to the fact here, that his teaching, so far as it concerns unorganised nature, is very defective and unserviceable, as in the fundamental conceptions of mechanics and physics he accepts the most gross errors, which is the less pardonable, since before him the Pythagoreans and Empedocles had been upon the right path and had taught much better. Empedocles indeed, as we learn from Aristotle's second book, De cœlo (c. 1, p. 284), had already grasped the conception of a tangential force arising from rotation, and counteracting gravity, which Aristotle again rejects. Quite the reverse, however, is Aristotle's relation to the investigation of organised nature. This is his field; here the wealth of his knowledge, the keenness of his observation, nay, sometimes the depth of his insight, astonish us. Thus, to give just one example, he already knew the antagonism in which in the ruminants the horns and the teeth of the upper jaw stand to each other, on account of which, therefore, the latter are wanting where the former are found, and conversely (De partib. anim., iii. 2). Hence then, also his correct estimation of final causes.
Chapter XXVII. On Instinct And Mechanical Tendency
It is as if nature had wished, in the mechanical tendencies of animals, to give the investigator an illustrative commentary upon her works, according to final causes and the admirable design of her organised productions which is thereby introduced. For these mechanical tendencies show most clearly that creatures can work with the greatest decision and definiteness towards an end which they do not know, nay, of which they have no idea. Such, for instance, is the bird's nest, the spider's web, the ant-lion's pitfall, the ingenious bee-hive, the marvellous termite dwelling, &c., at least for those individual animals that carry them out for the first time; for neither the form of the perfected work nor the use of it can be known to them. Precisely so, however, does organising nature work; and therefore in the preceding chapter I gave the paradoxical explanation of the final cause, that it is a motive which acts without being known. And as in working from mechanical tendency that which is active is evidently and confessedly the will, so is it also really the will which is active in the working of organising nature.
One might say, the will of animal creatures is set in motion in two different ways: either by motivation or by instinct; thus from without, or from within; by an external occasion, or by an internal tendency; the former is explicable because it lies before us without, the latter is inexplicable because it is merely internal. But, more closely considered, the contrast between the two is not so sharp, indeed ultimately it runs back into a difference of degree. The motive also only acts under the assumption of an inner tendency, i. e., a definite quality of will which is called its character. The motive in each case only gives to this a definite direction – individualises it for the concrete case. So also instinct, although a definite tendency of the will, does not act entirely, like a spring, from within; but it also waits for some external circumstance necessarily demanded for its action, which at least determines the time of its manifestation; such is, for the migrating bird, the season of the year; for the bird that builds its nest, the fact of pregnancy and the presence of the material for the nest; for the bee it is, for the beginning of the structure, the basket or the hollow tree, and for the following work many individually appearing circumstances; for the spider, it is a well-adapted corner; for the caterpillar, the suitable leaf; for egg-laying insects, the for the most part very specially determined and often rare place, where the hatched larvæ will at once find their nourishment, and so on. It follows from this that in works of mechanical tendency it is primarily the instinct of these animals that is active, yet subordinated also to their intellect. The instinct gives the universal, the rule; the intellect the particular, the application, in that it directs the detail of the execution, in which therefore the work of these animals clearly adapts itself to the circumstances of the existing case. According to all this, the difference between instinct and mere character is to be fixed thus: Instinct is a character which is only set in motion by a quite specially determined motive, and on this account the action that proceeds from it is always exactly of the same kind; while the character which is possessed by every species of animal and every individual man is certainly a permanent and unalterable quality of will, which can yet be set in motion by very different motives, and adapts itself to these; and on account of this the action proceeding from it may, according to its material quality, be very different, but yet will always bear the stamp of the same character, and will therefore express and reveal this; so that for the knowledge of this character the material quality of the action in which it appears is essentially a matter of indifference. Accordingly we might explain instinct as a character which is beyond all measure one-sided and strictly determined. It follows from this exposition that being determined by mere motivation presupposes a certain width of the sphere of knowledge, and consequently a more fully developed intellect: therefore it is peculiar to the higher animals, quite pre-eminently, however, to man; while being determined by instinct only demands as much intellect as is necessary to apprehend the one quite specially determined motive, which alone and exclusively becomes the occasion for the manifestation of the instinct. Therefore it is found in the case of an exceedingly limited sphere of knowledge, and consequently, as a rule, and in the highest degree, only in animals of the lower classes, especially insects. Since, accordingly, the actions of these animals only require an exceedingly simple and small motivation from without, the medium of this, thus the intellect or the brain, is very slightly developed in them, and their outward actions are for the most part under the same guidance as the inner, follow upon mere stimuli, physiological functions, thus the ganglion system. This is, then, in their case excessively developed; their principal nerve-stem runs under the belly in the form of two cords, which at every limb of the body form a ganglion little inferior to the brain in size, and, according to Cuvier, this nerve-stem is an analogue not so much of the spinal cord as of the great sympathetic nerve. According to all this, instinct and action through mere motivation, stand in a certain antagonism, in consequence of which the former has its maximum in insects, and the latter in man, and the actuation of other animals lies between the two in manifold gradations according as in each the cerebral or the ganglion system is preponderatingly developed. Just because the instinctive action and the ingenious contrivances of insects are principally directed from the ganglion system, if we regard them as proceeding from the brain alone, and wish to explain them accordingly, we fall into absurdities, because we then apply a false key. The same circumstance, however, imparts to their action a remarkable likeness to that of somnambulists, which indeed is also explained as arising from the fact that, instead of the brain, the sympathetic nerve has undertaken the conduct of the outward actions also; insects are accordingly, to a certain extent, natural somnambulists. Things which we cannot get at directly we must make comprehensible to ourselves by means of an analogy. What has just been referred to will accomplish this in a high degree when assisted by the fact that in Kieser's “Tellurismus” (vol. ii. p. 250) a case is mentioned “in which the command of the mesmerist to the somnambulist to perform a definite action in a waking state was carried out by him when he awoke, without remembering the command.” Thus it was as if he must perform that action without rightly knowing why. Certainly this has the greatest resemblance to what goes on in the case of mechanical instincts in insects. The young spider feels that it must spin its web, although it neither knows nor understands the aim of it. We are
