CHAPTER II

THE DIVERGENT DIRECTIONS OF THE EVOLUTION OF LIFE. TORPOR, INTELLIGENCE,

INSTINCT

The evolution movement would be a simple one, and we should soon have

been able to determine its direction, if life had described a single

course, like that of a solid ball shot from a cannon. But it proceeds

rather like a shell, which suddenly bursts into fragments, which

fragments, being themselves shells, burst in their turn into fragments

destined to burst again, and so on for a time incommensurably long. We

perceive only what is nearest to us, namely, the scattered movements of

the pulverized explosions. From them we have to go back, stage by stage,

to the original movement.

When a shell bursts, the particular way it breaks is explained both by

the explosive force of the powder it contains and by the resistance of

the metal. So of the way life breaks into individuals and species. It

depends, we think, on two series of causes: the resistance life meets

from inert matter, and the explosive force--due to an unstable balance

of tendencies--which life bears within itself.

The resistance of inert matter was the obstacle that had first to be

overcome. Life seems to have succeeded in this by dint of humility, by

making itself very small and very insinuating, bending to physical and

chemical forces, consenting even to go a part of the way with them, like

the switch that adopts for a while the direction of the rail it is

endeavoring to leave. Of phenomena in the simplest forms of life, it is

hard to say whether they are still physical and chemical or whether they

are already vital. Life had to enter thus into the habits of inert

matter, in order to draw it little by little, magnetized, as it were, to

another track. The animate forms that first appeared were therefore of

extreme simplicity. They were probably tiny masses of scarcely

differentiated protoplasm, outwardly resembling the amoeba observable

to-day, but possessed of the tremendous internal push that was to raise

them even to the highest forms of life. That in virtue of this push the

first organisms sought to grow as much as possible, seems likely. But

organized matter has a limit of expansion that is very quickly reached;

beyond a certain point it divides instead of growing. Ages of effort and

prodigies of subtlety were probably necessary for life to get past this

new obstacle. It succeeded in inducing an increasing number of elements,

ready to divide, to remain united. By the division of labor it knotted

between them an indissoluble bond. The complex and quasi-discontinuous

organism is thus made to function as would a continuous living mass

which had simply grown bigger.

But the real and profound causes of division were those which life bore

within its bosom. For life is tendency, and the essence of a tendency is

to develop in the form of a sheaf, creating, by its very growth,

divergent directions among which its impetus is divided. This we observe

in ourselves, in the evolution of that special tendency which we call

our character. Each of us, glancing back over his history, will find

that his child-personality, though indivisible, united in itself divers

persons, which could remain blended just because they were in their

nascent state: this indecision, so charged with promise, is one of the

greatest charms of childhood. But these interwoven personalities become

incompatible in course of growth, and, as each of us can live but one

life, a choice must perforce be made. We choose in reality without

ceasing; without ceasing, also, we abandon many things. The route we

pursue in time is strewn with the remains of all that we began to be, of

all that we might have become. But nature, which has at command an

incalculable number of lives, is in no wise bound to make such

sacrifices. She preserves the different tendencies that have bifurcated

with their growth. She creates with them diverging series of species

that will evolve separately.

These series may, moreover, be of unequal importance. The author who

begins a novel puts into his hero many things which he is obliged to

discard as he goes on. Perhaps he will take them up later in other

books, and make new characters with them, who will seem like extracts

from, or rather like complements of, the first; but they will almost

always appear somewhat poor and limited in comparison with the original

character. So with regard to the evolution of life. The bifurcations on

the way have been numerous, but there have been many blind alleys beside

the two or three highways; and of these highways themselves, only one,

that which leads through the vertebrates up to man, has been wide enough

to allow free passage to the full breath of life. We get this impression

when we compare the societies of bees and ants, for instance, with human

societies. The former are admirably ordered and united, but stereotyped;

the latter are open to every sort of progress, but divided, and

incessantly at strife with themselves. The ideal would be a society

always in progress and always in equilibrium, but this ideal is perhaps

unrealizable: the two characteristics that would fain complete each

other, which do complete each other in their embryonic state, can no

longer abide together when they grow stronger. If one could speak,

otherwise than metaphorically, of an impulse toward social life, it

might be said that the brunt of the impulse was borne along the line of

evolution ending at man, and that the rest of it was collected on the

road leading to the hymenoptera: the societies of ants and bees would

thus present the aspect complementary to ours. But this would be only a

manner of expression. There has been no particular impulse towards

social life; there is simply the general movement of life, which on

divergent lines is creating forms ever new. If societies should appear

on two of these lines, they ought to show divergence of paths at the

same time as community of impetus. They will thus develop two classes of

characteristics which we shall find vaguely complementary of each other.

So our study of the evolution movement will have to unravel a certain

number of divergent directions, and to appreciate the importance of what

has happened along each of them--in a word, to determine the nature of

the dissociated tendencies and estimate their relative proportion.

Combining these tendencies, then, we shall get an approximation, or

rather an imitation, of the indivisible motor principle whence their

impetus proceeds. Evolution will thus prove to be something entirely

different from a series of adaptations to circumstances, as mechanism

claims; entirely different also from the realization of a plan of the

whole, as maintained by the doctrine of finality.

* * * * *

That adaptation to environment is the necessary condition of evolution

we do not question for a moment. It is quite evident that a species

would disappear, should it fail to bend to the conditions of existence

which are imposed on it. But it is one thing to recognize that outer

circumstances are forces evolution must reckon with, another to claim

that they are the directing causes of evolution. This latter theory is

that of mechanism. It excludes absolutely the hypothesis of an original

impetus, I mean an internal push that has carried life, by more and more

complex forms, to higher and higher destinies. Yet this impetus is

evident, and a mere glance at fossil species shows us that life need not

have evolved at all, or might have evolved only in very restricted

limits, if it had chosen the alternative, much more convenient to

itself, of becoming anchylosed in its primitive forms. Certain

Foraminifera have not varied since the Silurian epoch. Unmoved witnesses

of the innumerable revolutions that have upheaved our planet, the

Lingulae are to-day what they were at the remotest times of the

paleozoic era.

The truth is that adaptation explains the sinuosities of the movement of

evolution, but not its general directions, still less the movement

itself.[51] The road that leads to the town is obliged to follow the ups

and downs of the hills; it _adapts itself_ to the accidents of the

ground; but the accidents of the ground are not the cause of the road,

nor have they given it its direction. At every moment they furnish it

with what is indispensable, namely, the soil on which it lies; but if we

consider the whole of the road, instead of each of its parts, the

accidents of the ground appear only as impediments or causes of delay,

for the road aims simply at the town and would fain be a straight line.

Just so as regards the evolution of life and the circumstances through

which it passes--with this difference, that evolution does not mark out

a solitary route, that it takes directions without aiming at ends, and

that it remains inventive even in its adaptations.

But, if the evolution of life is something other than a series of

adaptations to accidental circumstances, so also it is not the

realization of a plan. A plan is given in advance. It is represented, or

at least representable, before its realization. The complete execution

of it may be put off to a distant future, or even indefinitely; but the

idea is none the less formulable at the present time, in terms actually

given. If, on the contrary, evolution is a creation unceasingly renewed,

it creates, as it goes on, not only the forms of life, but the ideas

that will enable the intellect to understand it, the terms which will

serve to express it. That is to say that its future overflows its

present, and can not be sketched out therein in an idea.

There is the first error of finalism. It involves another, yet more

serious.

If life realizes a plan, it ought to manifest a greater harmony the

further it advances, just as the house shows better and better the idea

of the architect as stone is set upon stone. If, on the contrary, the

unity of life is to be found solely in the impetus that pushes it along

the road of time, the harmony is not in front, but behind. The unity is

derived from a _vis a tergo_: it is given at the start as an impulsion,

not placed at the end as an attraction. In communicating itself, the

impetus splits up more and more. Life, in proportion to its progress, is

scattered in manifestations which undoubtedly owe to their common origin

the fact that they are complementary to each other in certain aspects,

but which are none the less mutually incompatible and antagonistic. So

the discord between species will go on increasing. Indeed, we have as

yet only indicated the essential cause of it. We have supposed, for the

sake of simplicity, that each species received the impulsion in order to

pass it on to others, and that, in every direction in which life

evolves, the propagation is in a straight line. But, as a matter of

fact, there are species which are arrested; there are some that

retrogress. Evolution is not only a movement forward; in many cases we

observe a marking-time, and still more often a deviation or turning

back. It must be so, as we shall show further on, and the same causes

that divide the evolution movement often cause life to be diverted from

itself, hypnotized by the form it has just brought forth. Thence results

an increasing disorder. No doubt there is progress, if progress mean a

continual advance in the general direction determined by a first

impulsion; but this progress is accomplished only on the two or three

great lines of evolution on which forms ever more and more complex, ever

more and more high, appear; between these lines run a crowd of minor

paths in which, on the contrary, deviations, arrests, and set-backs, are

multiplied. The philosopher, who begins by laying down as a principle

that each detail is connected with some general plan of the whole, goes

from one disappointment to another as soon as he comes to examine the

facts; and, as he had put everything in the same rank, he finds that, as

the result of not allowing for accident, he must regard everything as

accidental. For accident, then, an allowance must first be made, and a

very liberal allowance. We must recognize that all is not coherent in

nature. By so doing, we shall be led to ascertain the centres around

which the incoherence crystallizes. This crystallization itself will

clarify the rest; the main directions will appear, in which life is

moving whilst developing the original impulse. True, we shall not

witness the detailed accomplishment of a plan. Nature is more and better

than a plan in course of realization. A plan is a term assigned to a

labor: it closes the future whose form it indicates. Before the

evolution of life, on the contrary, the portals of the future remain

wide open. It is a creation that goes on for ever in virtue of an

initial movement. This movement constitutes the unity of the organized

world--a prolific unity, of an infinite richness, superior to any that

the intellect could dream of, for the intellect is only one of its

aspects or products.

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 development 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 vary with their authors, with the theoretic views

inspiring them, and raise discussions 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 sure of not going

astray. Moreover, they alone are important to us; for we do not aim,

like the naturalist, 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

us: 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 come to naught. There is

not a single property of vegetable life that is not found, in some

degree, in certain animals; 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 manifestations. 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 the possession of certain characters, 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 alimentation. 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; so 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

Pinguicula, which are insectivorous plants. On the other hand, the

fungi, which occupy so considerable a place in the vegetable world, feed

like animals: 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 automatically 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 directions 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.[52] They might be called the abortive children of

the vegetable world. Their different species are like so many blind

alleys, as if, by renouncing the mode of alimentation customary amongst

vegetables, they had been brought to a standstill on the highway of

vegetable evolution. As to the Drosera, the Dionaea, and insectivorous

plants in general, they are fed by their roots, like 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 nourishment. In a general way, then, if we

attach less importance 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 sense-organs with which to recognize their prey,

locomotor organs to go and seize it, and a nervous system to coördinate

their movements with their sensations, 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 cellulose, 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 elements it can appropriate directly. It is true that

phenomena 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 insectivorous plants, such as the Drosera and

the Dionaea, to seize their prey. The leaf-movements of the acacia, the

sensitive 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.[53] 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 like 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

movements 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 world,

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 almost be

defined by them. But fixity and mobility, again, are only superficial

signs of tendencies that are still deeper.

Between mobility and consciousness there is an obvious relationship. No

doubt, the consciousness of the higher organisms seems bound up with

certain cerebral arrangements. 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 animal series, the more the nervous centres are

simplified, and the more, too, they separate from each other, till

finally the nervous elements disappear, merged in 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 incapable 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

reflex movement, 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 canalized, still

less concentrated into a system, there is something 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 intelligent hesitations of the latter, but which, partaking of both

it may be infinitesimally, is a reaction simply undecided, and therefore

vaguely conscious. This amounts to saying that the humblest organism is

conscious in proportion to its power to move _freely_. Is consciousness

here, in relation to movement, the effect or the cause? In one sense it

is the cause, since it has to direct locomotion. 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 rhizocephala, 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 differentiated, 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 direction 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.[54] The plant is 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 regained liberty of movement, and

awakens in just the degree to which the vegetable has reconquered this

liberty. Nevertheless, consciousness and unconsciousness mark the

directions in which the two kingdoms have developed, in this sense, that

to find the best specimens of consciousness in the animal we must

_ascend_ to the highest representatives of the series, whereas, to find

probable cases of vegetable consciousness, we must _descend_ as low as

possible in the scale of plants--down to the zoospores of the algae, for

instance, and, more generally, to those unicellular organisms which may

be said to hesitate between the vegetable form and animality. From this

standpoint, and in this measure, we should define the animal by

sensibility and awakened consciousness, the vegetable by consciousness

asleep and by insensibility.

To sum up, the vegetable manufactures organic substances directly with

mineral substances; as a rule, this aptitude enables it to dispense with

movement and so with feeling. Animals, which are obliged to go in search

of their food, have evolved in the direction of locomotor activity, and

consequently of a consciousness more and more distinct, more and more

ample.

* * * * *

Now, it seems to us most probable that the animal cell and the vegetable

cell are derived from a common stock, and that the first living

organisms oscillated between the vegetable and animal form,

participating in both at once. Indeed, we have just seen that the

characteristic tendencies of the evolution of the two kingdoms, although

divergent, coexist even now, both in the plant and in the animal. The

proportion alone differs. Ordinarily, one of the two tendencies covers

or crushes down the other, but in exceptional circumstances the

suppressed one starts up and regains the place it had lost. The

mobility and consciousness of the vegetable cell are not so sound asleep

that they cannot rouse themselves when circumstances permit or demand

it; and, on the other hand, the evolution of the animal kingdom has

always been retarded, or stopped, or dragged back, by the tendency it

has kept toward the vegetative life. However full, however overflowing

the activity of an animal species may appear, torpor and unconsciousness

are always lying in wait for it. It keeps up its rôle only by effort, at

the price of fatigue. Along the route on which the animal has evolved,

there have been numberless shortcomings and cases of decay, generally

associated with parasitic habits; they are so many shuntings on to the

vegetative life. Thus, everything bears out the belief that vegetable

and animal are descended from a common ancestor which united the

tendencies of both in a rudimentary state.

But the two tendencies mutually implied in this rudimentary form became

dissociated as they grew. Hence the world of plants with its fixity and

insensibility, hence the animals with their mobility and consciousness.

There is no need, in order to explain this dividing into two, to bring

in any mysterious force. It is enough to point out that the living being

leans naturally toward what is most convenient to it, and that

vegetables and animals have chosen two different kinds of convenience in

the way of procuring the carbon and nitrogen they need. Vegetables

continually and mechanically draw these elements from an environment

that continually provides it. Animals, by action that is discontinuous,

concentrated in certain moments, and conscious, go to find these bodies

in organisms that have already fixed them. They are two different ways

of being industrious, or perhaps we may prefer to say, of being idle.

For this very reason we doubt whether nervous elements, however

rudimentary, will ever be found in the plant. What corresponds in it to

the directing will of the animal is, we believe, the direction in which

it bends the energy of the solar radiation when it uses it to break the

connection of the carbon with the oxygen in carbonic acid. What

corresponds in it to the sensibility of the animal is the

impressionability, quite of its kind, of its chlorophyl light. Now, a

nervous system being pre-eminently a mechanism which serves as

intermediary between sensations and volitions, the true "nervous system"

of the plant seems to be the mechanism or rather chemicism _sui generis_

which serves as intermediary between the impressionability of its

chlorophyl to light and the producing of starch: which amounts to saying

that the plant can have no nervous elements, and that _the same impetus

that has led the animal to give itself nerves and nerve centres must

have ended, in the plant, in the chlorophyllian function_.[55]

* * * * *

This first glance over the organized world will enable us to ascertain

more precisely what unites the two kingdoms, and also what separates

them.

Suppose, as we suggested in the preceding chapter, that at the root of

life there is an effort to engraft on to the necessity of physical

forces the largest possible amount of _indetermination_. This effort

cannot result in the creation of energy, or, if it does, the quantity

created does not belong to the order of magnitude apprehended by our

senses and instruments of measurement, our experience and science. All

that the effort can do, then, is to make the best of a pre-existing

energy which it finds at its disposal. Now, it finds only one way of

succeeding in this, namely, to secure such an accumulation of potential

energy from matter, that it can get, at any moment, the amount of work

it needs for its action, simply by pulling a trigger. The effort itself

possesses only that power of releasing. But the work of releasing,

although always the same and always smaller than any given quantity,

will be the more effective the heavier the weight it makes fall and the

greater the height--or, in other words, the greater the sum of potential

energy accumulated and disposable. As a matter of fact, the principal

source of energy usable on the surface of our planet is the sun. So the

problem was this: to obtain from the sun that it should partially and

provisionally suspend, here and there, on the surface of the earth, its

continual outpour of usable energy, and store a certain quantity of it,

in the form of unused energy, in appropriate reservoirs, whence it could

be drawn at the desired moment, at the desired spot, in the desired

direction. The substances forming the food of animals are just such

reservoirs. Made of very complex molecules holding a considerable amount

of chemical energy in the potential state, they are like explosives

which only need a spark to set free the energy stored within them. Now,

it is probable that life tended at the beginning to compass at one and

the same time both the manufacture of the explosive and the explosion by

which it is utilized. In this case, the same organism that had directly

stored the energy of the solar radiation would have expended it in free

movements in space. And for that reason we must presume that the first

living beings sought on the one hand to accumulate, without ceasing,

energy borrowed from the sun, and on the other hand to expend it, in a

discontinuous and explosive way, in movements of locomotion. Even

to-day, perhaps, a chlorophyl-bearing Infusorian such as the Euglena may

symbolize this primordial tendency of life, though in a mean form,

incapable of evolving. Is the divergent development of the two kingdoms

related to what one may call the oblivion of each kingdom as regards one

of the two halves of the programme? Or rather, which is more likely, was

the very nature of the matter, that life found confronting it on our

planet, opposed to the possibility of the two tendencies evolving very

far together in the same organism? What is certain is that the vegetable

has trended principally in the first direction and the animal in the

second. But if, from the very first, in making the explosive, nature had

for object the explosion, then it is the evolution of the animal, rather

than that of the vegetable, that indicates, on the whole, the

fundamental direction of life.

The "harmony" of the two kingdoms, the complementary characters they

display, might then be due to the fact that they develop two tendencies

which at first were fused in one. The more the single original tendency

grows, the harder it finds it to keep united in the same living being

those two elements which in the rudimentary state implied each other.

Hence a parting in two, hence two divergent evolutions; hence also two

series of characters opposed in certain points, complementary in others,

but, whether opposed or complementary, always preserving an appearance

of kinship. While the animal evolved, not without accidents along the

way, toward a freer and freer expenditure of discontinuous energy, the

plant perfected rather its system of accumulation without moving. We

shall not dwell on this second point. Suffice it to say that the plant

must have been greatly benefited, in its turn, by a new division,

analogous to that between plants and animals. While the primitive

vegetable cell had to fix by itself both its carbon and its nitrogen, it

became able almost to give up the second of these two functions as soon

as microscopic vegetables came forward which leaned in this direction

exclusively, and even specialized diversely in this still complicated

business. The microbes that fix the nitrogen of the air and those which

convert the ammoniacal compounds into nitrous ones, and these again into

nitrates, have, by the same splitting up of a tendency primitively one,

rendered to the whole vegetable world the same kind of service as the

vegetables in general have rendered to animals. If a special kingdom

were to be made for these microscopic vegetables, it might be said that

in the microbes of the soil, the vegetables and the animals, we have

before us the _analysis_, carried out by the matter that life found at

its disposal on our planet, of all that life contained, at the outset,

in a state of reciprocal implication. Is this, properly speaking, a

"division of labor"? These words do not give the exact idea of

evolution, such as we conceive it. Wherever there is division of labor,

there is _association_ and also _convergence_ of effort. Now, the

evolution we are speaking of is never achieved by means of association,

but by _dissociation_; it never tends toward convergence, but toward

_divergence_ of efforts. The harmony between terms that are mutually

complementary in certain points is not, in our opinion, produced, in

course of progress, by a reciprocal adaptation; on the contrary, it is

complete only at the start. It arises from an original identity, from

the fact that the evolutionary process, splaying out like a sheaf,

sunders, in proportion to their simultaneous growth, terms which at

first completed each other so well that they coalesced.

Now, the elements into which a tendency splits up are far from

possessing the same importance, or, above all, the same power to evolve.

We have just distinguished three different kingdoms, if one may so

express it, in the organized world. While the first comprises only

microorganisms which have remained in the rudimentary state, animals and

vegetables have taken their flight toward very lofty fortunes. Such,

indeed, is generally the case when a tendency divides. Among the

divergent developments to which it gives rise, some go on indefinitely,

others come more or less quickly to the end of their tether. These

latter do not issue directly from the primitive tendency, but from one

of the elements into which it has divided; they are residual

developments made and left behind on the way by some truly elementary

tendency which continues to evolve. Now, these truly elementary

tendencies, we think, bear a mark by which they may be recognized.

This mark is like a trace, still visible in each, of what was in the

original tendency of which they represent the elementary directions. The

elements of a tendency are not like objects set beside each other in

space and mutually exclusive, but rather like psychic states, each of

which, although it be itself to begin with, yet partakes of others, and

so virtually includes in itself the whole personality to which it

belongs. There is no real manifestation of life, we said, that does not

show us, in a rudimentary or latent state, the characters of other

manifestations. Conversely, when we meet, on one line of evolution, a

recollection, so to speak, of what is developed along other lines, we

must conclude that we have before us dissociated elements of one and the

same original tendency. In this sense, vegetables and animals represent

the two great divergent developments of life. Though the plant is

distinguished from the animal by fixity and insensibility, movement and

consciousness sleep in it as recollections which may waken. But, beside

these normally sleeping recollections, there are others awake and

active, just those, namely, whose activity does not obstruct the

development of the elementary tendency itself. We may then formulate

this law: _When a tendency splits up in the course of its development,

each of the special tendencies which thus arise tries to preserve and

develop everything in the primitive tendency that is not incompatible

with the work for which it is specialized._ This explains precisely the

fact we dwelt on in the preceding chapter, viz., the formation of

identical complex mechanisms on independent lines of evolution. Certain

deep-seated analogies between the animal and the vegetable have probably

no other cause: sexual generation is perhaps only a luxury for the

plant, but to the animal it was a necessity, and the plant must have

been driven to it by the same impetus which impelled the animal thereto,

a primitive, original impetus, anterior to the separation of the two

kingdoms. The same may be said of the tendency of the vegetable towards

a growing complexity. This tendency is essential to the animal kingdom,

ever tormented by the need of more and more extended and effective

action. But the vegetable, condemned to fixity and insensibility,

exhibits the same tendency only because it received at the outset the

same impulsion. Recent experiments show that it varies at random when

the period of "mutation" arrives; whereas the animal must have evolved,

we believe, in much more definite directions. But we will not dwell

further on this original doubling of the modes of life. Let us come to

the evolution of animals, in which we are more particularly interested.

What constitutes animality, we said, is the faculty of utilizing a

releasing mechanism for the conversion of as much stored-up potential

energy as possible into "explosive" actions. In the beginning the

explosion is haphazard, and does not choose its direction. Thus the

amoeba thrusts out its pseudopodic prolongations in all directions at

once. But, as we rise in the animal scale, the form of the body itself

is observed to indicate a certain number of very definite directions

along which the energy travels. These directions are marked by so many

chains of nervous elements. Now, the nervous element has gradually

emerged from the barely differentiated mass of organized tissue. It may,

therefore, be surmised that in the nervous element, as soon as it

appears, and also in its appendages, the faculty of suddenly freeing the

gradually stored-up energy is concentrated. No doubt, every living cell

expends energy without ceasing, in order to maintain its equilibrium.

The vegetable cell, torpid from the start, is entirely absorbed in this

work of maintenance alone, as if it took for end what must at first have

been only a means. But, in the animal, all points to action, that is, to

the utilization of energy for movements from place to place. True, every

animal cell expends a good deal--often the whole--of the energy at its

disposal in keeping itself alive; but the organism as a whole tries to

attract as much energy as possible to those points where the locomotive

movements are effected. So that where a nervous system exists, with its

complementary sense-organs and motor apparatus, everything should happen

as if the rest of the body had, as its essential function, to prepare

for these and pass on to them, at the moment required, that force which

they are to liberate by a sort of explosion.

The part played by food amongst the higher animals is, indeed,

extremely complex. In the first place it serves to repair tissues, then

it provides the animal with the heat necessary to render it as

independent as possible of changes in external temperature. Thus it

preserves, supports, and maintains the organism in which the nervous

system is set and on which the nervous elements have to live. But these

nervous elements would have no reason for existence if the organism did

not pass to them, and especially to the muscles they control, a certain

energy to expend; and it may even be conjectured that there, in the

main, is the essential and ultimate destination of food. This does not

mean that the greater part of the food is used in this work. A state may

have to make enormous expenditure to secure the return of taxes, and the

sum which it will have to dispose of, after deducting the cost of

collection, will perhaps be very small: that sum is, none the less, the

reason for the tax and for all that has been spent to obtain its return.

So it is with the energy which the animal demands of its food.

Many facts seem to indicate that the nervous and muscular elements stand

in this relation towards the rest of the organism. Glance first at the

distribution of alimentary substances among the different elements of

the living body. These substances fall into two classes, one the

quaternary or albuminoid, the other the ternary, including the

carbohydrates and the fats. The albuminoids are properly plastic,

destined to repair the tissues--although, owing to the carbon they

contain, they are capable of providing energy on occasion. But the

function of supplying energy has devolved more particularly on the

second class of substances: these, being deposited in the cell rather

than forming part of its substance, convey to it, in the form of

chemical potential, an expansive energy that may be directly converted

into either movement or heat. In short, the chief function of the

albuminoids is to repair the machine, while the function of the other

class of substances is to supply power. It is natural that the

albuminoids should have no specially allotted destination, since every

part of the machine has to be maintained. But not so with the other

substances. The carbohydrates are distributed very unequally, and this

inequality of distribution seems to us in the highest degree

instructive.

Conveyed by the arterial blood in the form of glucose, these substances

are deposited, in the form of glycogen, in the different cells forming

the tissues. We know that one of the principal functions of the liver is

to maintain at a constant level the quantity of glucose held by the

blood, by means of the reserves of glycogen secreted by the hepatic

cells. Now, in this circulation of glucose and accumulation of glycogen,

it is easy to see that the effect is as if the whole effort of the

organism were directed towards providing with potential energy the

elements of both the muscular and the nervous tissues. The organism

proceeds differently in the two cases, but it arrives at the same

result. In the first case, it provides the muscle-cell with a large

reserve deposited in advance: the quantity of glycogen contained in the

muscles is, indeed, enormous in comparison with what is found in the

other tissues. In the nervous tissue, on the contrary, the reserve is

small (the nervous elements, whose function is merely to liberate the

potential energy stored in the muscle, never have to furnish much work

at one time); but the remarkable thing is that this reserve is restored

by the blood at the very moment that it is expended, so that the nerve

is instantly recharged with potential energy. Muscular tissue and

nervous tissue are, therefore, both privileged, the one in that it is

stocked with a large reserve of energy, the other in that it is always

served at the instant it is in need and to the exact extent of its

requirements.

More particularly, it is from the sensori-motor system that the call for

glycogen, the potential energy, comes, as if the rest of the organism

were simply there in order to transmit force to the nervous system and

to the muscles which the nerves control. True, when we think of the part

played by the nervous system (even the sensori-motor system) as

regulator of the organic life, it may well be asked whether, in this

exchange of good offices between it and the rest of the body, the

nervous system is indeed a master that the body serves. But we shall

already incline to this hypothesis when we consider, even in the static

state only, the distribution of potential energy among the tissues; and

we shall be entirely convinced of it when we reflect upon the conditions

in which the energy is expended and restored. For suppose the

sensori-motor system is a system like the others, of the same rank as

the others. Borne by the whole of the organism, it will wait until an

excess of chemical potential is supplied to it before it performs any

work. In other words, it is the production of glycogen which will

regulate the consumption by the nerves and muscles. On the contrary, if

the sensori-motor system is the actual master, the duration and extent

of its action will be independent, to a certain extent at least, of the

reserve of glycogen that it holds, and even of that contained in the

whole of the organism. It will perform work, and the other tissues will

have to arrange as they can to supply it with potential energy. Now,

this is precisely what does take place, as is shown in particular by the

experiments of Morat and Dufourt.[56] While the glycogenic function of

the liver depends on the action of the excitory nerves which control it,

the action of these nerves is subordinated to the action of those which

stimulate the locomotor muscles--in this sense, that the muscles begin

by expending without calculation, thus consuming glycogen, impoverishing

the blood of its glucose, and finally causing the liver, which has had

to pour into the impoverished blood some of its reserve of glycogen, to

manufacture a fresh supply. From the sensori-motor system, then,

everything starts; on that system everything converges; and we may say,

without metaphor, that the rest of the organism is at its service.

Consider again what happens in a prolonged fast. It is a remarkable fact

that in animals that have died of hunger the brain is found to be almost

unimpaired, while the other organs have lost more or less of their

weight and their cells have undergone profound changes.[57] It seems as

though the rest of the body had sustained the nervous system to the last

extremity, treating itself simply as the means of which the nervous

system is the end.

To sum up: if we agree, in short, to understand by "the sensori-motor

system" the cerebro-spinal nervous system together with the sensorial

apparatus in which it is prolonged and the locomotor muscles it

controls, we may say that a higher organism is essentially a

sensori-motor system installed on systems of digestion, respiration,

circulation, secretion, etc., whose function it is to repair, cleanse

and protect it, to create an unvarying internal environment for it, and

above all to pass it potential energy to convert into locomotive

movement.[58] It is true that the more the nervous function is

perfected, the more must the functions required to maintain it develop,

and the more exacting, consequently, they become for themselves. As the

nervous activity has emerged from the protoplasmic mass in which it was

almost drowned, it has had to summon around itself activities of all

kinds for its support. These could only be developed on other

activities, which again implied others, and so on indefinitely. Thus it

is that the complexity of functioning of the higher organisms goes on to

infinity. The study of one of these organisms therefore takes us round

in a circle, as if everything was a means to everything else. But the

circle has a centre, none the less, and that is the system of nervous

elements stretching between the sensory organs and the motor apparatus.

We will not dwell here on a point we have treated at length in a former

work. Let us merely recall that the progress of the nervous system has

been effected both in the direction of a more precise adaptation of

movements and in that of a greater latitude left to the living being to

choose between them. These two tendencies may appear antagonistic, and

indeed they are so; but a nervous chain, even in its most rudimentary

form, successfully reconciles them. On the one hand, it marks a

well-defined track between one point of the periphery and another, the

one sensory, the other motor. It has therefore canalized an activity

which was originally diffused in the protoplasmic mass. But, on the

other hand, the elements that compose it are probably discontinuous; at

any rate, even supposing they anastomose, they exhibit a _functional_

discontinuity, for each of them ends in a kind of cross-road where

probably the nervous current may choose its course. From the humblest

Monera to the best endowed insects, and up to the most intelligent

vertebrates, the progress realized has been above all a progress of the

nervous system, coupled at every stage with all the new constructions

and complications of mechanism that this progress required. As we

foreshadowed in the beginning of this work, the rôle of life is to

insert some _indetermination_ into matter. Indeterminate, _i.e._

unforeseeable, are the forms it creates in the course of its evolution.

More and more indeterminate also, more and more free, is the activity to

which these forms serve as the vehicle. A nervous system, with neurones

placed end to end in such wise that, at the extremity of each, manifold

ways open in which manifold questions present themselves, is a veritable

_reservoir of indetermination_. That the main energy of the vital

impulse has been spent in creating apparatus of this kind is, we

believe, what a glance over the organized world as a whole easily shows.

But concerning the vital impulse itself a few explanations are

necessary.

* * * * *

It must not be forgotten that the force which is evolving throughout the

organized world is a limited force, which is always seeking to transcend

itself and always remains inadequate to the work it would fain produce.

The errors and puerilities of radical finalism are due to the

misapprehension of this point. It has represented the whole of the

living world as a construction, and a construction analogous to a human

work. All the pieces have been arranged with a view to the best possible

functioning of the machine. Each species has its reason for existence,

its part to play, its allotted place; and all join together, as it were,

in a musical concert, wherein the seeming discords are really meant to

bring out a fundamental harmony. In short, all goes on in nature as in

the works of human genius, where, though the result may be trifling,

there is at least perfect adequacy between the object made and the work

of making it.

Nothing of the kind in the evolution of life. There, the disproportion

is striking between the work and the result. From the bottom to the top

of the organized world we do indeed find one great effort; but most

often this effort turns short, sometimes paralyzed by contrary forces,

sometimes diverted from what it should do by what it does, absorbed by

the form it is engaged in taking, hypnotized by it as by a mirror. Even

in its most perfect works, though it seems to have triumphed over

external resistances and also over its own, it is at the mercy of the

materiality which it has had to assume. It is what each of us may

experience in himself. Our freedom, in the very movements by which it is

affirmed, creates the growing habits that will stifle it if it fails to

renew itself by a constant effort: it is dogged by automatism. The most

living thought becomes frigid in the formula that expresses it. The word

turns against the idea.

The letter kills the spirit. And our most ardent enthusiasm, as soon as

it is externalized into action, is so naturally congealed into the cold

calculation of interest or vanity, the one takes so easily the shape of

the other, that we might confuse them together, doubt our own

sincerity, deny goodness and love, if we did not know that the dead

retain for a time the features of the living.

The profound cause of this discordance lies in an irremediable

difference of rhythm. Life in general is mobility itself; particular

manifestations of life accept this mobility reluctantly, and constantly

lag behind. It is always going ahead; they want to mark time. Evolution

in general would fain go on in a straight line; each special evolution

is a kind of circle. Like eddies of dust raised by the wind as it

passes, the living turn upon themselves, borne up by the great blast of

life. They are therefore relatively stable, and counterfeit immobility

so well that we treat each of them as a _thing_ rather than as a

_progress_, forgetting that the very permanence of their form is only

the outline of a movement. At times, however, in a fleeting vision, the

invisible breath that bears them is materialized before our eyes. We

have this sudden illumination before certain forms of maternal love, so

striking, and in most animals so touching, observable even in the

solicitude of the plant for its seed. This love, in which some have seen

the great mystery of life, may possibly deliver us life's secret. It

shows us each generation leaning over the generation that shall follow.

It allows us a glimpse of the fact that the living being is above all a

thoroughfare, and that the essence of life is in the movement by which

life is transmitted.

This contrast between life in general, and the forms in which it is

manifested, has everywhere the same character. It might be said that

life tends toward the utmost possible action, but that each species

prefers to contribute the slightest possible effort. Regarded in what

constitutes its true essence, namely, as a transition from species to

species, life is a continually growing action. But each of the species,

through which life passes, aims only at its own convenience. It goes

for that which demands the least labor. Absorbed in the form it is about

to take, it falls into a partial sleep, in which it ignores almost all

the rest of life; it fashions itself so as to take the greatest possible

advantage of its immediate environment with the least possible trouble.

Accordingly, the act by which life goes forward to the creation of a new

form, and the act by which this form is shaped, are two different and

often antagonistic movements. The first is continuous with the second,

but cannot continue in it without being drawn aside from its direction,

as would happen to a man leaping, if, in order to clear the obstacle, he

had to turn his eyes from it and look at himself all the while.

Living forms are, by their very definition, forms that are able to live.

In whatever way the adaptation of the organism to its circumstances is

explained, it has necessarily been sufficient, since the species has

subsisted. In this sense, each of the successive species that

paleontology and zoology describes was a _success_ carried off by life.

But we get a very different impression when we refer each species to the

movement that has left it behind on its way, instead of to the

conditions into which it has been set. Often this movement has turned

aside; very often, too, it has stopped short; what was to have been a

thoroughfare has become a terminus. From this new point of view, failure

seems the rule, success exceptional and always imperfect. We shall see

that, of the four main directions along which animal life bent its

course, two have led to blind alleys, and, in the other two, the effort

has generally been out of proportion to the result.

Documents are lacking to reconstruct this history in detail, but we can

make out its main lines. We have already said that animals and

vegetables must have separated soon from their common stock, the

vegetable falling asleep in immobility, the animal, on the contrary,

becoming more and more awake and marching on to the conquest of a

nervous system. Probably the effort of the animal kingdom resulted in

creating organisms still very simple, but endowed with a certain freedom

of action, and, above all, with a shape so undecided that it could lend

itself to any future determination. These animals may have resembled

some of our worms, but with this difference, however, that the worms

living to-day, to which they could be compared, are but the empty and

fixed examples of infinitely plastic forms, pregnant with an unlimited

future, the common stock of the echinoderms, molluscs, arthropods, and

vertebrates.

One danger lay in wait for them, one obstacle which might have stopped

the soaring course of animal life. There is one peculiarity with which

we cannot help being struck when glancing over the fauna of primitive

times, namely, the imprisonment of the animal in a more or less solid

sheath, which must have obstructed and often even paralyzed its

movements. The molluscs of that time had a shell more universally than

those of to-day. The arthropods in general were provided with a

carapace; most of them were crustaceans. The more ancient fishes had a

bony sheath of extreme hardness.[59] The explanation of this general

fact should be sought, we believe, in a tendency of soft organisms to

defend themselves against one another by making themselves, as far as

possible, undevourable. Each species, in the act by which it comes into

being, trends towards that which is most expedient. Just as among

primitive organisms there were some that turned towards animal life by

refusing to manufacture organic out of inorganic material and taking

organic substances ready made from organisms that had turned toward the

vegetative life, so, among the animal species themselves, many contrived

to live at the expense of other animals. For an organism that is animal,

that is to say mobile, can avail itself of its mobility to go in search

of defenseless animals, and feed on them quite as well as on vegetables.

So, the more species became mobile, the more they became voracious and

dangerous to one another. Hence a sudden arrest of the entire animal

world in its progress towards higher and higher mobility; for the hard

and calcareous skin of the echinoderm, the shell of the mollusc, the

carapace of the crustacean and the ganoid breast-plate of the ancient

fishes probably all originated in a common effort of the animal species

to protect themselves against hostile species. But this breast-plate,

behind which the animal took shelter, constrained it in its movements

and sometimes fixed it in one place. If the vegetable renounced

consciousness in wrapping itself in a cellulose membrane, the animal

that shut itself up in a citadel or in armor condemned itself to a

partial slumber. In this torpor the echinoderms and even the molluscs

live to-day. Probably arthropods and vertebrates were threatened with it

too. They escaped, however, and to this fortunate circumstance is due

the expansion of the highest forms of life.

In two directions, in fact, we see the impulse of life to movement

getting the upper hand again. The fishes exchanged their ganoid

breast-plate for scales. Long before that, the insects had appeared,

also disencumbered of the breast-plate that had protected their

ancestors. Both supplemented the insufficiency of their protective

covering by an agility that enabled them to escape their enemies, and

also to assume the offensive, to choose the place and the moment of

encounter. We see a progress of the same kind in the evolution of human

armaments. The first impulse is to seek shelter; the second, which is

the better, is to become as supple as possible for flight and above all

for attack--attack being the most effective means of defense. So the

heavy hoplite was supplanted by the legionary; the knight, clad in

armor, had to give place to the light free-moving infantryman; and in a

general way, in the evolution of life, just as in the evolution of human

societies and of individual destinies, the greatest successes have been

for those who have accepted the heaviest risks.

Evidently, then, it was to the animal's interest to make itself more

mobile. As we said when speaking of adaptation in general, any

transformation of a species can be explained by its own particular

interest. This will give the immediate cause of the variation, but often

only the most superficial cause. The profound cause is the impulse which

thrust life into the world, which made it divide into vegetables and

animals, which shunted the animal on to suppleness of form, and which,

at a certain moment, in the animal kingdom threatened with torpor,

secured that, on some points at least, it should rouse itself up and

move forward.

On the two paths along which the vertebrates and arthropods have

separately evolved, development (apart from retrogressions connected

with parasitism or any other cause) has consisted above all in the

progress of the sensori-motor nervous system. Mobility and suppleness

were sought for, and also--through many experimental attempts, and not

without a tendency to excess of substance and brute force at the

start--variety of movements. But this quest itself took place in

divergent directions. A glance at the nervous system of the arthropods

and that of the vertebrates shows us the difference. In the arthropods,

the body is formed of a series more or less long of rings set together;

motor activity is thus distributed amongst a varying--sometimes a

considerable--number of appendages, each of which has its special

function. In the vertebrates, activity is concentrated in two pairs of

members only, and these organs perform functions which depend much less

strictly on their form.[60] The independence becomes complete in man,

whose hand is capable of any kind of work.

That, at least, is what we see. But behind what is seen there is what

may be surmised--two powers, immanent in life and originally

intermingled, which were bound to part company in course of growth.

To define these powers, we must consider, in the evolution both of the

arthropods and the vertebrates, the species which mark the culminating

point of each. How is this point to be determined? Here again, to aim at

geometrical precision will lead us astray. There is no single simple

sign by which we can recognize that one species is more advanced than

another on the same line of evolution. There are manifold characters,

that must be compared and weighed in each particular case, in order to

ascertain to what extent they are essential or accidental and how far

they must be taken into account.

It is unquestionable, for example, that _success_ is the most general

criterion of superiority, the two terms being, up to a certain point,

synonymous. By success must be understood, so far as the living being is

concerned, an aptitude to develop in the most diverse environments,

through the greatest possible variety of obstacles, so as to cover the

widest possible extent of ground. A species which claims the entire

earth for its domain is truly a dominating and consequently superior

species. Such is the human species, which represents the culminating

point of the evolution of the vertebrates. But such also are, in the

series of the articulate, the insects and in particular certain

hymenoptera. It has been said of the ants that, as man is lord of the

soil, they are lords of the sub-soil.

On the other hand, a group of species that has appeared late may be a

group of degenerates; but, for that, some special cause of retrogression

must have intervened. By right, this group should be superior to the

group from which it is derived, since it would correspond to a more

advanced stage of evolution. Now man is probably the latest comer of the

vertebrates;[61] and in the insect series no species is later than the

hymenoptera, unless it be the lepidoptera, which are probably

degenerates, living parasitically on flowering plants.

So, by different ways, we are led to the same conclusion. The evolution

of the arthropods reaches its culminating point in the insect, and in

particular in the hymenoptera, as that of the vertebrates in man. Now,

since instinct is nowhere so developed as in the insect world, and in no

group of insects so marvelously as in the hymenoptera, it may be said

that the whole evolution of the animal kingdom, apart from

retrogressions towards vegetative life, has taken place on two divergent

paths, one of which led to instinct and the other to intelligence.

Vegetative torpor, instinct, and intelligence--these, then, are the

elements that coincided in the vital impulsion common to plants and

animals, and which, in the course of a development in which they were

made manifest in the most unforeseen forms, have been dissociated by the

very fact of their growth. _The cardinal error which, from Aristotle

onwards, has vitiated most of the philosophies of nature, is to see in

vegetative, instinctive and rational life, three successive degrees of

the development of one and the same tendency, whereas they are three

divergent directions of an activity that has split up as it grew._ The

difference between them is not a difference of intensity, nor, more

generally, of degree, but of kind.

* * * * *

It is important to investigate this point. We have seen in the case of

vegetable and animal life how they are at once mutually complementary

and mutually antagonistic. Now we must show that intelligence and

instinct also are opposite and complementary. But let us first explain

why we are generally led to regard them as activities of which one is

superior to the other and based upon it, whereas in reality they are not

things of the same order: they have not succeeded one another, nor can

we assign to them different grades.

It is because intelligence and instinct, having originally been

interpenetrating, retain something of their common origin. Neither is

ever found in a pure state. We said that in the plant the consciousness

and mobility of the animal, which lie dormant, can be awakened; and that

the animal lives under the constant menace of being drawn aside to the

vegetative life. The two tendencies--that of the plant and that of the

animal--were so thoroughly interpenetrating, to begin with, that there

has never been a complete severance between them: they haunt each other

continually; everywhere we find them mingled; it is the proportion that

differs. So with intelligence and instinct. There is no intelligence in

which some traces of instinct are not to be discovered, more especially

no instinct that is not surrounded with a fringe of intelligence. It is

this fringe of intelligence that has been the cause of so many

misunderstandings. From the fact that instinct is always more or less

intelligent, it has been concluded that instinct and intelligence are

things of the same kind, that there is only a difference of complexity

or perfection between them, and, above all, that one of the two is

expressible in terms of the other. In reality, they accompany each other

only because they are complementary, and they are complementary only

because they are different, what is instinctive in instinct being

opposite to what is intelligent in intelligence.

We are bound to dwell on this point. It is one of the utmost importance.

Let us say at the outset that the distinctions we are going to make will

be too sharply drawn, just because we wish to define in instinct what is

instinctive, and in intelligence what is intelligent, whereas all

concrete instinct is mingled with intelligence, as all real intelligence

is penetrated by instinct. Moreover, neither intelligence nor instinct

lends itself to rigid definition: they are tendencies, and not things.

Also, it must not be forgotten that in the present chapter we are

considering intelligence and instinct as going out of life which

deposits them along its course. Now the life manifested by an organism

is, in our view, a certain effort to obtain certain things from the

material world. No wonder, therefore, if it is the diversity of this

effort that strikes us in instinct and intelligence, and if we see in

these two modes of psychical activity, above all else, two different

methods of action on inert matter. This rather narrow view of them has

the advantage of giving us an objective means of distinguishing them. In

return, however, it gives us, of intelligence in general and of instinct

in general, only the mean position above and below which both constantly

oscillate. For that reason the reader must expect to see in what follows

only a diagrammatic drawing, in which the respective outlines of

intelligence and instinct are sharper than they should be, and in which

the shading-off which comes from the indecision of each and from their

reciprocal encroachment on one another is neglected. In a matter so

obscure, we cannot strive too hard for clearness. It will always be easy

afterwards to soften the outlines and to correct what is too geometrical

in the drawing--in short, to replace the rigidity of a diagram by the

suppleness of life.

* * * * *

To what date is it agreed to ascribe the appearance of man on the earth?

To the period when the first weapons, the first tools, were made. The

memorable quarrel over the discovery of Boucher de Perthes in the quarry

of Moulin-Quignon is not forgotten. The question was whether real

hatchets had been found or merely bits of flint accidentally broken. But

that, supposing they were hatchets, we were indeed in the presence of

intelligence, and more particularly of _human_ intelligence, no one

doubted for an instant. Now let us open a collection of anecdotes on the

intelligence of animals: we shall see that besides many acts explicable

by imitation or by the automatic association of images, there are some

that we do not hesitate to call intelligent: foremost among them are

those that bear witness to some idea of manufacture, whether the animal

life succeeds in fashioning a crude instrument or uses for its profit an

object made by man. The animals that rank immediately after man in the

matter of intelligence, the apes and elephants, are those that can use

an artificial instrument occasionally. Below, but not very far from

them, come those that _recognize_ a constructed object: for example, the

fox, which knows quite well that a trap is a trap. No doubt, there is

intelligence wherever there is inference; but inference, which consists

in an inflection of past experience in the direction of present

experience, is already a beginning of invention. Invention becomes

complete when it is materialized in a manufactured instrument. Towards

that achievement the intelligence of animals tends as towards an ideal.

And though, ordinarily, it does not yet succeed in fashioning artificial

objects and in making use of them, it is preparing for this by the very

variations which it performs on the instincts furnished by nature. As

regards human intelligence, it has not been sufficiently noted that

mechanical invention has been from the first its essential feature, that

even to-day our social life gravitates around the manufacture and use of

artificial instruments, that the inventions which strew the road of

progress have also traced its direction. This we hardly realize, because

it takes us longer to change ourselves than to change our tools. Our

individual and even social habits survive a good while the circumstances

for which they were made, so that the ultimate effects of an invention

are not observed until its novelty is already out of sight. A century

has elapsed since the invention of the steam-engine, and we are only

just beginning to feel the depths of the shock it gave us. But the

revolution it has effected in industry has nevertheless upset human

relations altogether. New ideas are arising, new feelings are on the way

to flower. In thousands of years, when, seen from the distance, only the

broad lines of the present age will still be visible, our wars and our

revolutions will count for little, even supposing they are remembered

at all; but the steam-engine, and the procession of inventions of every

kind that accompanied it, will perhaps be spoken of as we speak of the

bronze or of the chipped stone of prehistoric times: it will serve to

define an age.[62] If we could rid ourselves of all pride, if, to define

our species, we kept strictly to what the historic and the prehistoric

periods show us to be the constant characteristic of man and of

intelligence, we should say not _Homo sapiens_, but _Homo faber_. In

short, _intelligence, considered in what seems to be its original

feature, is the faculty of manufacturing artificial objects, especially

tools to make tools, and of indefinitely varying the manufacture_.

Now, does an unintelligent animal also possess tools or machines? Yes,

certainly, but here the instrument forms a part of the body that uses

it; and, corresponding to this instrument, there is an _instinct_ that

knows how to use it. True, it cannot be maintained that _all_ instincts

consist in a natural ability to use an inborn mechanism. Such a

definition would not apply to the instincts which Romanes called

"secondary"; and more than one "primary" instinct would not come under

it. But this definition, like that which we have provisionally given of

intelligence, determines at least the ideal limit toward which the very

numerous forms of instinct are traveling. Indeed, it has often been

pointed out that most instincts are only the continuance, or rather the

consummation, of the work of organization itself. Where does the

activity of instinct begin? and where does that of nature end? We cannot

tell. In the metamorphoses of the larva into the nymph and into the

perfect insect, metamorphoses that often require appropriate action and

a kind of initiative on the part of the larva, there is no sharp line of

demarcation between the instinct of the animal and the organizing work

of living matter. We may say, as we will, either that instinct organizes

the instruments it is about to use, or that the process of organization

is continued in the instinct that has to use the organ. The most

marvelous instincts of the insect do nothing but develop its special

structure into movements: indeed, where social life divides the labor

among different individuals, and thus allots them different instincts, a

corresponding difference of structure is observed: the polymorphism of

ants, bees, wasps and certain pseudoneuroptera is well known. Thus, if

we consider only those typical cases in which the complete triumph of

intelligence and of instinct is seen, we find this essential difference

between them: _instinct perfected is a faculty of using and even of

constructing organized instruments; intelligence perfected is the

faculty of making and using unorganized instruments_.

The advantages and drawbacks of these two modes of activity are obvious.

Instinct finds the appropriate instrument at hand: this instrument,

which makes and repairs itself, which presents, like all the works of

nature, an infinite complexity of detail combined with a marvelous

simplicity of function, does at once, when required, what it is called

upon to do, without difficulty and with a perfection that is often

wonderful. In return, it retains an almost invariable structure, since a

modification of it involves a modification of the species. Instinct is

therefore necessarily specialized, being nothing but the utilization of

a specific instrument for a specific object. The instrument constructed

intelligently, on the contrary, is an imperfect instrument. It costs an

effort. It is generally troublesome to handle. But, as it is made of

unorganized matter, it can take any form whatsoever, serve any purpose,

free the living being from every new difficulty that arises and bestow

on it an unlimited number of powers. Whilst it is inferior to the

natural instrument for the satisfaction of immediate wants, its

advantage over it is the greater, the less urgent the need. Above all,

it reacts on the nature of the being that constructs it; for in calling

on him to exercise a new function, it confers on him, so to speak, a

richer organization, being an artificial organ by which the natural

organism is extended. For every need that it satisfies, it creates a new

need; and so, instead of closing, like instinct, the round of action

within which the animal tends to move automatically, it lays open to

activity an unlimited field into which it is driven further and further,

and made more and more free. But this advantage of intelligence over

instinct only appears at a late stage, when intelligence, having raised

construction to a higher degree, proceeds to construct constructive

machinery. At the outset, the advantages and drawbacks of the artificial

instrument and of the natural instrument balance so well that it is hard

to foretell which of the two will secure to the living being the greater

empire over nature.

We may surmise that they began by being implied in each other, that the

original psychical activity included both at once, and that, if we went

far enough back into the past, we should find instincts more nearly

approaching intelligence than those of our insects, intelligence nearer

to instinct than that of our vertebrates, intelligence and instinct

being, in this elementary condition, prisoners of a matter which they

are not yet able to control. If the force immanent in life were an

unlimited force, it might perhaps have developed instinct and

intelligence together, and to any extent, in the same organisms. But

everything seems to indicate that this force is limited, and that it

soon exhausts itself in its very manifestation. It is hard for it to go

far in several directions at once: it must choose. Now, it has the

choice between two modes of acting on the material world: it can either

effect this action _directly_ by creating an _organized_ instrument to

work with; or else it can effect it _indirectly_ through an organism

which, instead of possessing the required instrument naturally, will

itself construct it by fashioning inorganic matter. Hence intelligence

and instinct, which diverge more and more as they develop, but which

never entirely separate from each other. On the one hand, the most

perfect instinct of the insect is accompanied by gleams of intelligence,

if only in the choice of place, time and materials of construction: the

bees, for example, when by exception they build in the open air, invent

new and really intelligent arrangements to adapt themselves to such new

conditions.[63] But, on the other hand, intelligence has even more need

of instinct than instinct has of intelligence; for the power to give

shape to crude matter involves already a superior degree of

organization, a degree to which the animal could not have risen, save on

the wings of instinct. So, while nature has frankly evolved in the

direction of instinct in the arthropods, we observe in almost all the

vertebrates the striving after rather than the expansion of

intelligence. It is instinct still which forms the basis of their

psychical activity; but intelligence is there, and would fain supersede

it. Intelligence does not yet succeed in inventing instruments; but at

least it tries to, by performing as many variations as possible on the

instinct which it would like to dispense with. It gains complete

self-possession only in man, and this triumph is attested by the very

insufficiency of the natural means at man's disposal for defense against

his enemies, against cold and hunger. This insufficiency, when we strive

to fathom its significance, acquires the value of a prehistoric

document; it is the final leave-taking between intelligence and

instinct. But it is no less true that nature must have hesitated between

two modes of psychical activity--one assured of immediate success, but

limited in its effects; the other hazardous, but whose conquests, if it

should reach independence, might be extended indefinitely. Here again,

then, the greatest success was achieved on the side of the greatest

risk. _Instinct and intelligence therefore represent two divergent

solutions, equally fitting, of one and the same problem._

There ensue, it is true, profound differences of internal structure

between instinct and intelligence. We shall dwell only on those that

concern our present study. Let us say, then, that instinct and

intelligence imply two radically different kinds of knowledge. But some

explanations are first of all necessary on the subject of consciousness

in general.