Lamarck, the Founder of Evolution Part 31

_On the Transportation of the force-producing Movements in the Interior of Animals._

"If nature were confined to the employment of its first means--namely, of a force entirely external and foreign to the animal--its work would have remained very important; the animals would have remained machines totally pa.s.sive, and she would never have given origin in any of these living beings to the admirable phenomena of sensibility, of inmost feelings of existence which result therefrom, of the power of action, finally, of ideas, by which she can create the most wonderful of all, that of thought--in a word, intelligence.

"But, wis.h.i.+ng to attain these grand results, she has by slow degrees prepared the means, in gradually giving consistence to the internal parts of animals; in differentiating the organs, and in multiplying and farther forming the fluids contained, etc., after which she has transported into the interior of these animals that force productive of movements and of actions which in truth it would not dominate at first, but which she has come to place, in great part, at their disposition when their organization should become very much more perfect.

"Indeed, from the time that the animal organization had sufficiently advanced in its structure to possess a nervous system--even slightly developed, as in insects--the animals provided with this organization were endowed with an intimate sense of their existence, and from that time the force productive of movements was conveyed into the very interior of the animal.

"I have already made it evident that this internal force which produces movements and actions should derive its origin in the intimate feeling of existence which animals with a nervous system possess, and that this feeling, solicited or aroused by needs, should then start into motion the subtile fluid contained in the nerves and carry it to the muscles which should act, this producing the actions which the needs require.

"Moreover, every want felt produces an emotion in the inner feeling of the individual which experiences it; and from this emotion of the feeling in question arises the force which gives origin to the movement of the parts which are placed in activity....

"Thus, in the animals which possess the power of acting--namely, the force productive of movements and actions--the inner feeling, which on each occasion originates this force, being excited by some need, places in action the power or force in question; excites the movement of displacement in the subtile fluid of the nerves--which the ancients called _animal spirits_; directs this fluid towards that of its organs which any want impels to action; finally makes this same fluid flow back into its habitual reservoirs when the needs no longer require the organ to act.

"The inner feeling takes the place of the _will_; for it is now important to consider that every animal which does not possess the special organ in which or by which it executes thoughts, judgments, etc., has in reality no will, does not make a choice, and consequently cannot control the movements which its inner feeling excites. _Instinct_ directs these actions, and we shall see that this direction always results from emotions of the inner feeling, in which intelligence has no part, and from the organization even which the habits have modified, in such a manner that the needs of animals which are in this category, being necessarily limited and always the same in the same species, the inner feeling and, consequently, the power of acting, always produces the same actions.

"It is not the same in animals which besides a nervous system have a brain [the author meaning the higher vertebrates], and which make comparisons, judgments, thoughts, etc. These same animals control more or less their power of action according to the degree of perfection of their brain; and although they are still strongly subjected to the results of their habits, which have modified their structure, they enjoy more or less freedom of the will, can choose, and can vary their acts, or at least some of them."

Lamarck then treats of the consumption and exhaustion of the nervous fluid in the production of animal movements, resulting in fatigue.

He next occupies himself with the origin of the inclination to the same actions, and of instinct in animals.

"The cause of the well-known phenomenon which constrains almost all animals to always perform the same acts, and that which gives rise in man to a propensity (_penchant_) to repeat every action, becoming habitual, a.s.suredly merits investigation.

"The animals which are only 'sensible'[184]--namely, which possess no brain, cannot think, reason, or perform intelligent acts, and their perceptions being often very confused--do not reason and can scarcely vary their actions. They are, then, invariably bound by habits. Thus the insects, which of all animals endowed with feeling have the least perfect nervous system,[185] have perceptions of objects which affect them, and seem to have memory of them when they are repeated. Yet they can vary their actions and change their habits, though they do not possess the organ whose acts could give them the means.

"_On the Instincts of Animals._

"We define instinct as the sum (_ensemble_) of the decisions (_determinations_) of animals in their actions; and, indeed, some have thought that these determinations were the product of a rational choice, and consequently the fruit of experience. Others, says Cabanis, may think with the observers of all ages that several of these decisions should not be ascribed to any kind of reasoning, and that, without ceasing as for that to have their source in physical sensibility, they are most often formed without the will of the individuals able to have any other part than in better directing the execution. It should be added, without the will having any part in it; for when it does not act, it does not, of course, direct the execution.

"If it had been considered that all the animals which enjoy the power of sensation have their inner feeling susceptible of being aroused by their needs, and that the movements of their nervous fluids, which result from these emotions, are constantly directed by this inner sentiment and by habits, then it has been felt that in all the animals deprived of intelligence all the decisions of action can never be the result of a rational choice, of judgment, of profitable experience--in a word, of will--but that they are subjected to needs which certain sensations excite, and which awaken the inclinations which urge them on.

"In the animals even which enjoy the power of performing certain intelligent acts, it is still more often the inner feeling and the inclinations originating from habits which decide, without choice, the acts which animals perform.

"Moreover, although the executing power of movements and of actions, as also the cause which directs them, should be entirely internal, it is not well, as has been done,[186] to limit to internal impressions the primary cause or provocation of these acts, with the intention to restrict to external impressions that which provokes intelligent acts; for, from what few facts are known bearing on these considerations, we are convinced that, either way, the causes which arouse and provoke acts are sometimes internal and sometimes external, that these same causes give rise in reality to impressions all of which act internally.

"According to the idea generally attached to the word _instinct_ the faculty which this word expresses is considered as a light which illuminates and guides animals in their actions, and which is with them what reason is to us. No one has shown that instinct can be a force which calls into action; that this force acts effectively without any partic.i.p.ation of the will, and that it is constantly directed by acquired inclinations."

There are, the author states, two kinds of causes which can arouse the inner feeling (organic sense)--namely, those which depend on intellectual acts, and those which, without arising from it, immediately excite it and force it to direct its power of acting in the direction of acquired inclinations.

"These are the only causes of this last kind, which const.i.tute all the acts of _instinct_; and as these acts are not the result of deliberation, of choice, of judgment, the actions which arise from them always satisfy, surely and without error, the wants felt and the propensities arising from habits.

"Hence, _instinct_ in animals is an inclination which necessitates that from sensations provoked while giving rise to wants the animal is impelled to act without the partic.i.p.ation of any thought or any act of the will.

"This propensity owes to the organization what the habits have modified in its favor, and it is excited by impressions and wants which arouse the organic sense of the individual and put it in the way of sending the nervous fluid in the direction which the propensity in activity needs to the muscles to be placed in action.

"I have already said that the habit of exercising such an organ, or such a part of the body, to satisfy the needs which often spring up, should give to the subtile fluid which changes its place where is to be operated the power which causes action so great a facility in moving towards this organ, where it has been so often employed, that this habit should in a way become inherent in the nature of the individual, which is unable to change it.

"Moreover, the wants of animals possessing a nervous system being, in each case, dependent on the Structure of these organisms, are:

"1. Of obtaining any kind of food;

"2. Of yielding to s.e.xual fecundation which excites in them certain sensations;

"3. Of avoiding pain;

"4. Of seeking pleasure or happiness.

"To satisfy these wants they contract different kinds of habits, which are transformed into so many propensities, which they can neither resist nor change. From this originate their habitual actions, and their special propensities to which we give the name of instinct.[187]

"This propensity of animals to preserve their habits and to renew the actions resulting from them being once acquired, is then propagated by means of reproduction or generation, which preserves the organization and the disposition of parts in the state thus attained, so that this same propensity already exists in the new individuals even before they have exercised it.

"It is thus that the same habits and the same _instinct_ are perpetuated from generation to generation in the different species or races of animals, without offering any notable variation,[188] so long as it does not suffer change in the circ.u.mstances essential to the mode of life."

"_On the Industry of Certain Animals._

"In those animals which have no brain that which we call _industry_ as applied to certain of their actions does not deserve such a name, for it is a mistake to attribute to them a faculty which they do not possess.

"Propensities transmitted and received by heredity (_generation_); habits of performing complicated actions, and which result from these acquired propensities; finally, different difficulties gradually and habitually overcome by as many emotions of the organic sense (_sentiment interieur_), const.i.tute the sum of actions which are always the same in the individuals of the same race, to which we inconsiderately give the name of _industry_.

"The instinct of animals being formed by the habit of satisfying the four kinds of wants mentioned above, and resulting from the propensities acquired for a long time which urge them on in a way determined for each species, there comes to pa.s.s, in the case of some, only a complication in the actions which can satisfy these four kinds of wants, or certain of them, and, indeed, only the different difficulties necessary to be overcome have gradually compelled the animal to extend and make contrivances, and have led it, without choice or any intellectual act, but only by the emotions of the organic sense, to perform such and such acts.

"Hence the origin, in certain animals, of different complicated actions, which has been called _industry_, and which are so enthusiastically admired, because it has always been supposed, at least tacitly, that these actions were contrived and deliberately planned, which is plainly erroneous. They are evidently the fruit of a necessity which has expanded and directed the habits of the animals performing them, and which renders them such as we observe.

"What I have just said is especially applicable to the invertebrate animals, in which there enters no act of intelligence. None of these can indeed freely vary its actions; none of them has the power of abandoning what we call its _industry_ to adopt any other kind.

"There is, then, nothing wonderful in the supposed industry of the ant-lion (_Myrmeleon formica-leo_), which, having thrown up a hillock of movable sand, waits until its booty is thrown down to the bottom of its funnel by the showers of sand to become its victim; also there is none in the manoeuvre of the oyster, which, to satisfy all its wants, does nothing but open and close its sh.e.l.l. So long as their organization is not changed they will always, both of them, do what we see them do, and they will do it neither voluntarily nor rationally.

"This is not the case with the vertebrate animals, and it is among them, especially in the birds and mammals, that we observe in their actions traces of a true _industry_; because in difficult cases their intelligence, in spite of their propensity to habits, can aid them in varying their actions. These acts, however, are not common, and are only slightly manifested in certain races which have exercised them more, as we have had frequent occasion to remark."

Lamarck then (chapter vi.) examines into the nature of the _will_, which he says is really the principle underlying all the actions of animals.

The will, he says, is one of the results of thought, the result of a reflux of a portion of the nervous fluid towards the parts which are to act.

He compares the brain to a register on which are imprinted ideas of all kinds acquired by the individual, so that this individual provokes at will an effusion of the nervous fluid on this register, and directs it to any particular page. The remainder of the second volume (chapter vii.) is devoted to the understanding, its origin and that of ideas. The following additions relative to chapters vii. and viii. of the first part of this work are from vol. ii., pp. 451-466.

In the last of June, 1809, the menagerie of the Museum of Natural History having received a Phoca (_Phoca vitulina_), Lamarck, as he says, had the opportunity of observing its movements and habits. After describing its habits in swimming and moving on land and observing its relation to the clawed mammals, he says his main object is to remark that the seals do not have the hind legs arranged in the same direction as the axis of their body, because these animals are constrained to habitually use them to form a caudal fin, closing and widening, by spreading their digits, the paddle (_palette_) which results from their union.

"The morses, on the contrary, which are accustomed to feed on gra.s.s near the sh.o.r.e, never use their hind feet as a caudal fin; but their feet are united together with the tail, and cannot separate. Thus in animals of similar origin we see a new proof of the effect of habits on the form and structure of organs."

He then turns to the flying mammals, such as the flying squirrel (_Sciurus volans_, _aerobates_, _petaurista_, _sagitta_, and _volucella_), and then explains the origin of their adaptation for flying leaps.

"These animals, more modern than the seals, having the habit of extending their limbs while leaping to form a sort of _parachute_, can _only_ make a very prolonged leap when they glide down from a tree or spring only a short distance from one tree to another. Now, by frequent repet.i.tions of such leaps, in the individuals of these races the skin of their sides is expanded on each side into a loose membrane, which connects the hind and fore legs, and which, enclosing a volume of air, prevents their sudden falling. These animals are, moreover, without membranes between the fingers and toes.

"The Galeopithecus (_Lemur volans_), undoubtedly a more ancient form but with the same habits as the flying squirrel (_Pteromys Geoff._), has the skin of the _flancs_ more ample, still more developed, connecting not only the hinder with the fore legs, but in addition the fingers and the tail with the hind feet. Moreover, they leap much farther than the flying squirrels, and even make a sort of flight.[189]

"Finally, the different bats are probably mammals still older than the Galeopithecus, in the habit of extending their membrane and even their fingers to encompa.s.s a greater volume of air, so as to sustain their bodies when they fly out into the air.

"By these habits, for so long a period contracted and preserved, the bats have obtained not only lateral membranes, but also an extraordinary elongation of the fingers of their fore feet (with the exception of the thumb), between which are these very ample membranes uniting them; so that these membranes of the hands become continuous with those of the flanks, and with those which connect the tail with the two hind feet, forming in these animals great membranous wings with which they fly perfectly, as everybody knows.