Like radical finalism, although in a vaguer form, our philosophy

represents the organized world as a harmonious whole. But this harmony

is far from being as perfect as it has been claimed to be. It admits of

much discord, because each species, each individual even, retains only a

certain impetus from the universal vital impulsion and tends to use this

energy in its own interest. In this consists _adaptation_. The species

and the individual thus think only of themselves--whence arises a

possible conflict with other forms of life. Harmony, therefore, does

not exist in fact; it exists rather in principle; I mean that the

original impetus is a _common_ impetus, and the higher we ascend the

stream of life the more do diverse tendencies appear complementary to

each other. Thus the wind at a street-corner divides into diverging

currents which are all one and the same gust. Harmony, or rather

"complementarity," is revealed only in the mass, in tendencies rather

than in states. Especially (and this is the point on which finalism has

been most seriously mistaken) harmony is rather behind us than before.

It is due to an identity of impulsion and not to a common aspiration. It

would be futile to try to assign to life an end, in the human sense of

the word. To speak of an end is to think of a pre-existing model which

has only to be realized. It is to suppose, therefore, that all is given,

and that the future can be read in the present. It is to believe that

life, in its movement and in its entirety, goes to work like our

intellect, which is only a motionless and fragmentary view of life, and

which naturally takes its stand outside of time. Life, on the contrary,

progresses and _endures_ in time. Of course, when once the road has been

traveled, we can glance over it, mark its direction, note this in

psychological terms and speak as if there had been pursuit of an end.

Thus shall we speak ourselves. But, of the road which was going to be

traveled, the human mind could have nothing to say, for the road has

been created _pari passu_ with the act of traveling over it, being

nothing but the direction of this act itself. At every instant, then,

evolution must admit of a psychological interpretation which is, from

our point of view, the best interpretation; but this explanation has

neither value nor even significance except retrospectively. Never could

the finalistic interpretation, such as we shall propose it, be taken for

an anticipation of the future. It is a particular mode of viewing the

past in the light of the present. In short, the classic conception of

finality postulates at once too much and too little: it is both too wide

and too narrow. In explaining life by intellect, it limits too much the

meaning of life: intellect, such at least as we find it in ourselves,

has been fashioned by evolution during the course of progress; it is cut

out of something larger, or, rather, it is only the projection,

necessarily on a plane, of a reality that possesses both relief and

depth. It is this more comprehensive reality that true finalism ought to

reconstruct, or, rather, if possible, embrace in one view. But, on the

other hand, just because it goes beyond intellect--the faculty of

connecting the same with the same, of perceiving and also of producing

repetitions--this reality is undoubtedly creative, _i.e._ productive of

effects in which it expands and transcends its own being. These effects

were therefore not given in it in advance, and so it could not take them

for ends, although, when once produced, they admit of a rational

interpretation, like that of the manufactured article that has

reproduced a model. In short, the theory of final causes does not go far

enough when it confines itself to ascribing some intelligence to nature,

and it goes too far when it supposes a pre-existence of the future in

the present in the form of idea. And the second theory, which sins by

excess, is the outcome of the first, which sins by defect. In place of

intellect proper must be substituted the more comprehensive reality of

which intellect is only the contraction. The future then appears as

expanding the present: it was not, therefore, contained in the present

in the form of a represented end. And yet, once realized, it will

explain the present as much as the present explains it, and even more;

it must be viewed as an end as much as, and more than, a result. Our

intellect has a right to consider the future abstractly from its

habitual point of view, being itself an abstract view of the cause of

its own being.

It is true that the cause may then seem beyond our grasp. Already the

finalist theory of life eludes all precise verification. What if we go

beyond it in one of its directions? Here, in fact, after a necessary

digression, we are back at the question which we regard as essential:

can the insufficiency of mechanism be proved by facts? We said that if

this demonstration is possible, it is on condition of frankly accepting

the evolutionist hypothesis. We must now show that if mechanism is

insufficient to account for evolution, the way of proving this

insufficiency is not to stop at the classic conception of finality,

still less to contract or attenuate it, but, on the contrary, to go

further.

Let us indicate at once the principle of our demonstration. We said of

life that, from its origin, it is the continuation of one and the same

impetus, divided into divergent lines of evolution. Something has grown,

something has developed by a series of additions which have been so many

creations. This very development has brought about a dissociation of

tendencies which were unable to grow beyond a certain point without

becoming mutually incompatible. Strictly speaking, there is nothing to

prevent our imagining that the evolution of life might have taken place

in one single individual by means of a series of transformations spread

over thousands of ages. Or, instead of a single individual, any number

might be supposed, succeeding each other in a unilinear series. In both

cases evolution would have had, so to speak, one dimension only. But

evolution has actually taken place through millions of individuals, on

divergent lines, each ending at a crossing from which new paths radiate,

and so on indefinitely. If our hypothesis is justified, if the

essential causes working along these diverse roads are of psychological

nature, they must keep something in common in spite of the divergence of

their effects, as school-fellows long separated keep the same memories

of boyhood. Roads may fork or by-ways be opened along which dissociated

elements may evolve in an independent manner, but nevertheless it is in

virtue of the primitive impetus of the whole that the movement of the

parts continues. Something of the whole, therefore, must abide in the

parts; and this common element will be evident to us in some way,

perhaps by the presence of identical organs in very different organisms.

Suppose, for an instant, that the mechanistic explanation is the true

one: evolution must then have occurred through a series of accidents

added to one another, each new accident being preserved by selection if

it is advantageous to that sum of former advantageous accidents which

the present form of the living being represents. What likelihood is

there that, by two entirely different series of accidents being added

together, two entirely different evolutions will arrive at similar

results? The more two lines of evolution diverge, the less probability

is there that accidental outer influences or accidental inner variations

bring about the construction of the same apparatus upon them, especially

if there was no trace of this apparatus at the moment of divergence. But

such similarity of the two products would be natural, on the contrary,

on a hypothesis like ours: even in the latest channel there would be

something of the impulsion received at the source. _Pure mechanism,

then, would be refutable, and finality, in the special sense in which we

understand it, would be demonstrable in a certain aspect, if it could be

proved that life may manufacture the like apparatus, by unlike means, on

divergent lines of evolution; and the strength of the proof would be

proportional both to the divergency between the lines of evolution thus

chosen and to the complexity of the similar structures found in them._

It will be said that resemblance of structure is due to sameness of the

general conditions in which life has evolved, and that these permanent

outer conditions may have imposed the same direction on the forces

constructing this or that apparatus, in spite of the diversity of

transient outer influences and accidental inner changes. We are not, of

course, blind to the rôle which the concept of _adaptation_ plays in the

science of to-day. Biologists certainly do not all make the same use of

it. Some think the outer conditions capable of causing change in

organisms in a _direct_ manner, in a definite direction, through

physico-chemical alterations induced by them in the living substance;

such is the hypothesis of Eimer, for example. Others, more faithful to

the spirit of Darwinism, believe the influence of conditions works

_indirectly_ only, through favoring, in the struggle for life, those

representatives of a species which the chance of birth has best adapted

to the environment. In other words, some attribute a _positive_

influence to outer conditions, and say that they actually _give rise to_

variations, while the others say these conditions have only a _negative_

influence and merely _eliminate_ variations. But, in both cases, the

outer conditions are supposed to bring about a precise adjustment of the

organism to its circumstances. Both parties, then, will attempt to

explain mechanically, by adaptation to similar conditions, the

similarities of structure which we think are the strongest argument

against mechanism. So we must at once indicate in a general way, before

passing to the detail, why explanations from "adaptation" seem to us

insufficient.

Let us first remark that, of the two hypotheses just described, the

latter is the only one which is not equivocal. The Darwinian idea of

adaptation by automatic elimination of the unadapted is a simple and

clear idea. But, just because it attributes to the outer cause which

controls evolution a merely negative influence, it has great difficulty

in accounting for the progressive and, so to say, rectilinear

development of complex apparatus such as we are about to examine. How

much greater will this difficulty be in the case of the similar

structure of two extremely complex organs on two entirely different

lines of evolution! An accidental variation, however minute, implies the

working of a great number of small physical and chemical causes. An

accumulation of accidental variations, such as would be necessary to

produce a complex structure, requires therefore the concurrence of an

almost infinite number of infinitesimal causes. Why should these causes,

entirely accidental, recur the same, and in the same order, at different

points of space and time? No one will hold that this is the case, and

the Darwinian himself will probably merely maintain that identical

effects may arise from different causes, that more than one road leads

to the same spot. But let us not be fooled by a metaphor. The place

reached does not give the form of the road that leads there; while an

organic structure is just the accumulation of those small differences

which evolution has had to go through in order to achieve it. The

struggle for life and natural selection can be of no use to us in

solving this part of the problem, for we are not concerned here with

what has perished, we have to do only with what has survived. Now, we

see that identical structures have been formed on independent lines of

evolution by a gradual accumulation of effects. How can accidental

causes, occurring in an accidental order, be supposed to have repeatedly

come to the same result, the causes being infinitely numerous and the

effect infinitely complicated?

The principle of mechanism is that "the same causes produce the same

effects." This principle, of course, does not always imply that the same

effects must have the same causes; but it does involve this consequence

in the particular case in which the causes remain visible in the effect

that they produce and are indeed its constitutive elements. That two

walkers starting from different points and wandering at random should

finally meet, is no great wonder. But that, throughout their walk, they

should describe two identical curves exactly superposable on each other,

is altogether unlikely. The improbability will be the greater, the more

complicated the routes; and it will become impossibility, if the zigzags

are infinitely complicated. Now, what is this complexity of zigzags as

compared with that of an organ in which thousands of different cells,

each being itself a kind of organism, are arranged in a definite order?

Let us turn, then, to the other hypothesis, and see how it would solve

the problem. Adaptation, it says, is not merely elimination of the

unadapted; it is due to the positive influence of outer conditions that

have molded the organism on their own form. This time, similarity of

effects will be explained by similarity of cause. We shall remain,

apparently, in pure mechanism. But if we look closely, we shall see that

the explanation is merely verbal, that we are again the dupes of words,

and that the trick of the solution consists in taking the term

"adaptation" in two entirely different senses at the same time.

If I pour into the same glass, by turns, water and wine, the two liquids

will take the same form, and the sameness in form will be due to the

sameness in adaptation of content to container. Adaptation, here, really

means mechanical adjustment. The reason is that the form to which the

matter has adapted itself was there, ready-made, and has forced its own

shape on the matter. But, in the adaptation of an organism to the

circumstances it has to live in, where is the pre-existing form awaiting

its matter? The circumstances are not a mold into which life is inserted

and whose form life adopts: this is indeed to be fooled by a metaphor.

There is no form yet, and the life must create a form for itself, suited

to the circumstances which are made for it. It will have to make the

best of these circumstances, neutralize their inconveniences and utilize

their advantages--in short, respond to outer actions by building up a

machine which has no resemblance to them. Such adapting is not

_repeating_, but _replying_,--an entirely different thing. If there is

still adaptation, it will be in the sense in which one may say of the

solution of a problem of geometry, for example, that it is adapted to

the conditions. I grant indeed that adaptation so understood explains

why different evolutionary processes result in similar forms: the same

problem, of course, calls for the same solution. But it is necessary

then to introduce, as for the solution of a problem of geometry, an

intelligent activity, or at least a cause which behaves in the same way.

This is to bring in finality again, and a finality this time more than

ever charged with anthropomorphic elements. In a word, if the adaptation

is passive, if it is mere repetition in the relief of what the

conditions give in the mold, it will build up nothing that one tries to

make it build; and if it is active, capable of responding by a

calculated solution to the problem which is set out in the conditions,

that is going further than we do--too far, indeed, in our opinion--in

the direction we indicated in the beginning. But the truth is that there

is a surreptitious passing from one of these two meanings to the other,

a flight for refuge to the first whenever one is about to be caught _in

flagrante delicto_ of finalism by employing the second. It is really

the second which serves the usual practice of science, but it is the

first that generally provides its philosophy. In any _particular_ case

one talks as if the process of adaptation were an effort of the organism

to build up a machine capable of turning external circumstances to the

best possible account: then one speaks of adaptation _in general_ as if

it were the very impress of circumstances, passively received by an

indifferent matter.

But let us come to the examples. It would be interesting first to

institute here a general comparison between plants and animals. One

cannot fail to be struck with the parallel progress which has been

accomplished, on both sides, in the direction of sexuality. Not only is

fecundation itself the same in higher plants and in animals, since it

consists, in both, in the union of two nuclei that differ in their

properties and structure before their union and immediately after become

equivalent to each other; but the preparation of sexual elements goes on

in both under like conditions: it consists essentially in the reduction

of the number of chromosomes and the rejection of a certain quantity of

chromatic substance.[22] Yet vegetables and animals have evolved on

independent lines, favored by unlike circumstances, opposed by unlike

obstacles. Here are two great series which have gone on diverging. On

either line, thousands and thousands of causes have combined to

determine the morphological and functional evolution. Yet these

infinitely complicated causes have been consummated, in each series, in

the same effect. And this effect, could hardly be called a phenomenon of

"adaptation": where is the adaptation, where is the pressure of external

circumstances? There is no striking utility in sexual generation; it

has been interpreted in the most diverse ways; and some very acute

enquirers even regard the sexuality of the plant, at least, as a luxury

which nature might have dispensed with.[23] But we do not wish to dwell

on facts so disputed. The ambiguity of the term "adaptation," and the

necessity of transcending both the point of view of mechanical causality

and that of anthropomorphic finality, will stand out more clearly with

simpler examples. At all times the doctrine of finality has laid much

stress on the marvellous structure of the sense-organs, in order to

liken the work of nature to that of an intelligent workman. Now, since

these organs are found, in a rudimentary state, in the lower animals,

and since nature offers us many intermediaries between the pigment-spot

of the simplest organisms and the infinitely complex eye of the

vertebrates, it may just as well be alleged that the result has been

brought about by natural selection perfecting the organ automatically.

In short, if there is a case in which it seems justifiable to invoke

adaptation, it is this particular one. For there may be discussion about

the function and meaning of such a thing as sexual generation, in so far

as it is related to the conditions in which it occurs; but the relation

of the eye to light is obvious, and when we call this relation an

adaptation, we must know what we mean. If, then, we can show, in this

privileged case, the insufficiency of the principles invoked on both

sides, our demonstration will at once have reached a high degree of

generality.

Let us consider the example on which the advocates of finality have

always insisted: the structure of such an organ as the human eye. They

have had no difficulty in showing that in this extremely complicated

apparatus all the elements are marvelously co-ordinated. In order that

vision shall operate, says the author of a well-known book on _Final

Causes_, "the sclerotic membrane must become transparent in one point of

its surface, so as to enable luminous rays to pierce it;... the cornea

must correspond exactly with the opening of the socket;... behind this

transparent opening there must be refracting media;... there must be a

retina[24] at the extremity of the dark chamber;... perpendicular to the

retina there must be an innumerable quantity of transparent cones

permitting only the light directed in the line of their axes to reach

the nervous membrane,"[25] etc. etc. In reply, the advocate of final

causes has been invited to assume the evolutionist hypothesis.

Everything is marvelous, indeed, if one consider an eye like ours, in

which thousands of elements are coördinated in a single function. But

take the function at its origin, in the Infusorian, where it is reduced

to the mere impressionability (almost purely chemical) of a pigment-spot

to light: this function, possibly only an accidental fact in the

beginning, may have brought about a slight complication of the organ,

which again induced an improvement of the function. It may have done

this either directly, through some unknown mechanism, or indirectly,

merely through the effect of the advantages it brought to the living

being and the hold it thus offered to natural selection. Thus the

progressive formation of an eye as well contrived as ours would be

explained by an almost infinite number of actions and reactions between

the function and the organ, without the intervention of other than

mechanical causes.

The question is hard to decide, indeed, when put directly between the

function and the organ, as is done in the doctrine of finality, as also

mechanism itself does. For organ and function are terms of different

nature, and each conditions the other so closely that it is impossible

to say _a priori_ whether in expressing their relation we should begin

with the first, as does mechanism, or with the second, as finalism

requires. But the discussion would take an entirely different turn, we

think, if we began by comparing together two terms of the same nature,

an organ with an organ, instead of an organ with its function. In this

case, it would be possible to proceed little by little to a solution

more and more plausible, and there would be the more chance of a

successful issue the more resolutely we assumed the evolutionist

hypothesis.

Let us place side by side the eye of a vertebrate and that of a mollusc

such as the common Pecten. We find the same essential parts in each,

composed of analogous elements. The eye of the Pecten presents a retina,

a cornea, a lens of cellular structure like our own. There is even that

peculiar inversion of retinal elements which is not met with, in

general, in the retina of the invertebrates. Now, the origin of molluscs

may be a debated question, but, whatever opinion we hold, all are agreed

that molluscs and vertebrates separated from their common parent-stem

long before the appearance of an eye so complex as that of the Pecten.

Whence, then, the structural analogy?

Let us question on this point the two opposed systems of evolutionist

explanation in turn--the hypothesis of purely accidental variations, and

that of a variation directed in a definite way under the influence of

external conditions.

The first, as is well known, is presented to-day in two quite different

forms. Darwin spoke of very slight variations being accumulated by

natural selection. He was not ignorant of the facts of sudden variation;

but he thought these "sports," as he called them, were only

monstrosities incapable of perpetuating themselves; and he accounted for

the genesis of species by an accumulation of _insensible_

variations.[26] Such is still the opinion of many naturalists. It is

tending, however, to give way to the opposite idea that a new species

comes into being all at once by the simultaneous appearance of several

new characters, all somewhat different from the previous ones. This

latter hypothesis, already proposed by various authors, notably by

Bateson in a remarkable book,[27] has become deeply significant and

acquired great force since the striking experiments of Hugo de Vries.

This botanist, working on the _OEnothera Lamarckiana_, obtained at the

end of a few generations a certain number of new species. The theory he

deduces from his experiments is of the highest interest. Species pass

through alternate periods of stability and transformation. When the

period of "mutability" occurs, unexpected forms spring forth in a great

number of different directions.[28]--We will not attempt to take sides

between this hypothesis and that of insensible variations. Indeed,

perhaps both are partly true. We wish merely to point out that if the

variations invoked are accidental, they do not, whether small or great,

account for a similarity of structure such as we have cited.

Let us assume, to begin with, the Darwinian theory of insensible

variations, and suppose the occurrence of small differences due to

chance, and continually accumulating. It must not be forgotten that all

the parts of an organism are necessarily coördinated. Whether the

function be the effect of the organ or its cause, it matters little; one

point is certain--the organ will be of no use and will not give

selection a hold unless it functions. However the minute structure of

the retina may develop, and however complicated it may become, such

progress, instead of favoring vision, will probably hinder it if the

visual centres do not develop at the same time, as well as several parts

of the visual organ itself. If the variations are accidental, how can

they ever agree to arise in every part of the organ at the same time, in

such way that the organ will continue to perform its function? Darwin

quite understood this; it is one of the reasons why he regarded

variation as insensible.[29] For a difference which arises accidentally

at one point of the visual apparatus, if it be very slight, will not

hinder the functioning of the organ; and hence this first accidental

variation can, in a sense, _wait for_ complementary variations to

accumulate and raise vision to a higher degree of perfection. Granted;

but while the insensible variation does not hinder the functioning of

the eye, neither does it help it, so long as the variations that are

complementary do not occur. How, in that case, can the variation be

retained by natural selection? Unwittingly one will reason as if the

slight variation were a toothing stone set up by the organism and

reserved for a later construction. This hypothesis, so little

conformable to the Darwinian principle, is difficult enough to avoid

even in the case of an organ which has been developed along one single

main line of evolution, _e.g._ the vertebrate eye. But it is absolutely

forced upon us when we observe the likeness of structure of the

vertebrate eye and that of the molluscs. How could the same small

variations, incalculable in number, have ever occurred in the same

order on two independent lines of evolution, if they were purely

accidental? And how could they have been preserved by selection and

accumulated in both cases, the same in the same order, when each of

them, taken separately, was of no use?

Let us turn, then, to the hypothesis of sudden variations, and see

whether it will solve the problem. It certainly lessens the difficulty

on one point, but it makes it much worse on another. If the eye of the

mollusc and that of the vertebrate have both been raised to their

present form by a relatively small number of sudden leaps, I have less

difficulty in understanding the resemblance of the two organs than if

this resemblance were due to an incalculable number of infinitesimal

resemblances acquired successively: in both cases it is chance that

operates, but in the second case chance is not required to work the

miracle it would have to perform in the first. Not only is the number of

resemblances to be added somewhat reduced, but I can also understand

better how each could be preserved and added to the others; for the

elementary variation is now considerable enough to be an advantage to

the living being, and so to lend itself to the play of selection. But

here there arises another problem, no less formidable, viz., how do all

the parts of the visual apparatus, suddenly changed, remain so well

coördinated that the eye continues to exercise its function? For the

change of one part alone will make vision impossible, unless this change

is absolutely infinitesimal. The parts must then all change at once,

each consulting the others. I agree that a great number of uncoördinated

variations may indeed have arisen in less fortunate individuals, that

natural selection may have eliminated these, and that only the

combination fit to endure, capable of preserving and improving vision,

has survived. Still, this combination had to be produced. And, supposing

chance to have granted this favor once, can we admit that it repeats the

self-same favor in the course of the history of a species, so as to give

rise, every time, all at once, to new complications marvelously

regulated with reference to each other, and so related to former

complications as to go further on in the same direction? How,

especially, can we suppose that by a series of mere "accidents" these

sudden variations occur, the same, in the same order,--involving in each

case a perfect harmony of elements more and more numerous and

complex--along two independent lines of evolution?

The law of correlation will be invoked, of course; Darwin himself

appealed to it.[30] It will be alleged that a change is not localized in

a single point of the organism, but has its necessary recoil on other

points. The examples cited by Darwin remain classic: white cats with

blue eyes are generally deaf; hairless dogs have imperfect dentition,

etc.--Granted; but let us not play now on the word "correlation." A

collective whole of _solidary_ changes is one thing, a system of

_complementary_ changes--changes so coördinated as to keep up and even

improve the functioning of an organ under more complicated

conditions--is another. That an anomaly of the pilous system should be

accompanied by an anomaly of dentition is quite conceivable without our

having to call for a special principle of explanation; for hair and

teeth are similar formations,[31] and the same chemical change of the

germ that hinders the formation of hair would probably obstruct that of

teeth: it may be for the same sort of reason that white cats with blue

eyes are deaf. In these different examples the "correlative" changes are

only _solidary_ changes (not to mention the fact that they are really

_lesions_, namely, diminutions or suppressions, and not additions, which

makes a great difference). But when we speak of "correlative" changes

occurring suddenly in the different parts of the eye, we use the word in

an entirely new sense: this time there is a whole set of changes not

only simultaneous, not only bound together by community of origin, but

so coördinated that the organ keeps on performing the same simple

function, and even performs it better. That a change in the germ, which

influences the formation of the retina, may affect at the same time also

the formation of the cornea, the iris, the lens, the visual centres,

etc., I admit, if necessary, although they are formations that differ

much more from one another in their original nature than do probably

hair and teeth. But that all these simultaneous changes should occur in

such a way as to improve or even merely maintain vision, this is what,

in the hypothesis of sudden variation, I cannot admit, unless a

mysterious principle is to come in, whose duty it is to watch over the

interest of the function. But this would be to give up the idea of

"accidental" variation. In reality, these two senses of the word

"correlation" are often interchanged in the mind of the biologist, just

like the two senses of the word "adaptation." And the confusion is

almost legitimate in botany, that science in which the theory of the

formation of species by sudden variation rests on the firmest

experimental basis. In vegetables, function is far less narrowly bound

to form than in animals. Even profound morphological differences, such

as a change in the form of leaves, have no appreciable influence on the

exercise of function, and so do not require a whole system of

complementary changes for the plant to remain fit to survive. But it is

not so in the animal, especially in the case of an organ like the eye, a

very complex structure and very delicate function. Here it is impossible

to identify changes that are simply solidary with changes which are also

complementary. The two senses of the word "correlation" must be

carefully distinguished; it would be a downright paralogism to adopt one

of them in the premisses of the reasoning, and the other in the

conclusion. And this is just what is done when the principle of

correlation is invoked in explanations of _detail_ in order to account

for complementary variations, and then correlation _in general_ is

spoken of as if it were any group of variations provoked by any

variation of the germ. Thus, the notion of correlation is first used in

current science as it might be used by an advocate of finality; it is

understood that this is only a convenient way of expressing oneself,

that one will correct it and fall back on pure mechanism when explaining

the nature of the principles and turning from science to philosophy. And

one does then come back to pure mechanism, but only by giving a new

meaning to the word "correlation"--a meaning which would now make

correlation inapplicable to the detail it is called upon to explain.

To sum up, if the accidental variations that bring about evolution are

insensible variations, some good genius must be appealed to--the genius

of the future species--in order to preserve and accumulate these

variations, for selection will not look after this. If, on the other

hand, the accidental variations are sudden, then, for the previous

function to go on or for a new function to take its place, all the

changes that have happened together must be complementary. So we have to

fall back on the good genius again, this time to obtain the

_convergence_ of _simultaneous_ changes, as before to be assured of the

_continuity of direction_ of _successive_ variations. But in neither

case can parallel development of the same complex structures on

independent lines of evolution be due to a mere accumulation of

accidental variations. So we come to the second of the two great

hypotheses we have to examine. Suppose the variations are due, not to

accidental and inner causes, but to the direct influence of outer

circumstances. Let us see what line we should have to take, on this

hypothesis, to account for the resemblance of eye-structure in two

series that are independent of each other from the phylogenetic point of

view.

Though molluscs and vertebrates have evolved separately, both have

remained exposed to the influence of light. And light is a physical

cause bringing forth certain definite effects. Acting in a continuous

way, it has been able to produce a continuous variation in a constant

direction. Of course it is unlikely that the eye of the vertebrate and

that of the mollusc have been built up by a series of variations due to

simple chance. Admitting even that light enters into the case as an

instrument of selection, in order to allow only useful variations to

persist, there is no possibility that the play of chance, even thus

supervised from without, should bring about in both cases the same

juxtaposition of elements coördinated in the same way. But it would be

different supposing that light acted directly on the organized matter so

as to change its structure and somehow adapt this structure to its own

form. The resemblance of the two effects would then be explained by the

identity of the cause. The more and more complex eye would be something

like the deeper and deeper imprint of light on a matter which, being

organized, possesses a special aptitude for receiving it.

But can an organic structure be likened to an imprint? We have already

called attention to the ambiguity of the term "adaptation." The gradual

complication of a form which is being better and better adapted to the

mold of outward circumstances is one thing, the increasingly complex

structure of an instrument which derives more and more advantage from

these circumstances is another. In the former case, the matter merely

receives an imprint; in the second, it reacts positively, it solves a

problem. Obviously it is this second sense of the word "adapt" that is

used when one says that the eye has become better and better adapted to

the influence of light. But one passes more or less unconsciously from

this sense to the other, and a purely mechanistic biology will strive to

make the _passive_ adaptation of an inert matter, which submits to the

influence of its environment, mean the same as the _active_ adaptation

of an organism which derives from this influence an advantage it can

appropriate. It must be owned, indeed, that Nature herself appears to

invite our mind to confuse these two kinds of adaptation, for she

usually begins by a passive adaptation where, later on, she will build

up a mechanism for active response. Thus, in the case before us, it is

unquestionable that the first rudiment of the eye is found in the

pigment-spot of the lower organisms; this spot may indeed have been

produced physically, by the mere action of light, and there are a great

number of intermediaries between the simple spot of pigment and a

complicated eye like that of the vertebrates.--But, from the fact that

we pass from one thing to another by degrees, it does not follow that

the two things are of the same nature. From the fact that an orator

falls in, at first, with the passions of his audience in order to make

himself master of them, it will not be concluded that to _follow_ is the

same as to _lead_. Now, living matter seems to have no other means of

turning circumstances to good account than by adapting itself to them

passively at the outset. Where it has to direct a movement, it begins by

adopting it. Life proceeds by insinuation. The intermediate degrees

between a pigment-spot and an eye are nothing to the point: however

numerous the degrees, there will still be the same interval between the

pigment-spot and the eye as between a photograph and a photographic

apparatus. Certainly the photograph has been gradually turned into a

photographic apparatus; but could light alone, a physical force, ever

have provoked this change, and converted an impression left by it into a

machine capable of using it?

It may be claimed that considerations of utility are out of place here;

that the eye is not made to see, but that we see because we have eyes;

that the organ is what it is, and "utility" is a word by which we

designate the functional effects of the structure. But when I say that

the eye "makes use of" light, I do not merely mean that the eye is

capable of seeing; I allude to the very precise relations that exist

between this organ and the apparatus of locomotion. The retina of

vertebrates is prolonged in an optic nerve, which, again, is continued

by cerebral centres connected with motor mechanisms. Our eye makes use

of light in that it enables us to utilize, by movements of reaction, the

objects that we see to be advantageous, and to avoid those which we see

to be injurious. Now, of course, as light may have produced a

pigment-spot by physical means, so it can physically determine the

movements of certain organisms; ciliated Infusoria, for instance, react

to light. But no one would hold that the influence of light has

physically caused the formation of a nervous system, of a muscular

system, of an osseous system, all things which are continuous with the

apparatus of vision in vertebrate animals. The truth is, when one

speaks of the gradual formation of the eye, and, still more, when one

takes into account all that is inseparably connected with it, one brings

in something entirely different from the direct action of light. One

implicitly attributes to organized matter a certain capacity _sui

generis_, the mysterious power of building up very complicated machines

to utilize the simple excitation that it undergoes.

But this is just what is claimed to be unnecessary. Physics and

chemistry are said to give us the key to everything. Eimer's great work

is instructive in this respect. It is well known what persevering effort

this biologist has devoted to demonstrating that transformation is

brought about by the influence of the external on the internal,

continuously exerted in the same direction, and not, as Darwin held, by

accidental variations. His theory rests on observations of the highest

interest, of which the starting-point was the study of the course

followed by the color variation of the skin in certain lizards. Before

this, the already old experiments of Dorfmeister had shown that the same

chrysalis, according as it was submitted to cold or heat, gave rise to

very different butterflies, which had long been regarded as independent

species, _Vanessa levana_ and _Vanessa prorsa_: an intermediate

temperature produces an intermediate form. We might class with these

facts the important transformations observed in a little crustacean,

_Artemia salina_, when the salt of the water it lives in is increased or

diminished.[32] In these various experiments the external agent seems to

act as a cause of transformation. But what does the word "cause" mean

here? Without undertaking an exhaustive analysis of the idea of

causality, we will merely remark that three very different meanings of

this term are commonly confused. A cause may act by _impelling_,

_releasing_, or _unwinding_. The billiard-ball, that strikes another,

determines its movement by _impelling_. The spark that explodes the

powder acts by _releasing_. The gradual relaxing of the spring, that

makes the phonograph turn, _unwinds_ the melody inscribed on the

cylinder: if the melody which is played be the effect, and the relaxing

of the spring the cause, we must say that the cause acts by _unwinding_.

What distinguishes these three cases from each other is the greater or

less solidarity between the cause and the effect. In the first, the

quantity and quality of the effect vary with the quantity and quality of

the cause. In the second, neither quality nor quantity of the effect

varies with quality and quantity of the cause: the effect is invariable.

In the third, the quantity of the effect depends on the quantity of the

cause, but the cause does not influence the quality of the effect: the

longer the cylinder turns by the action of the spring, the more of the

melody I shall hear, but the nature of the melody, or of the part heard,

does not depend on the action of the spring. Only in the first case,

really, does cause _explain_ effect; in the others the effect is more or

less given in advance, and the antecedent invoked is--in different

degrees, of course--its occasion rather than its cause. Now, in saying

that the saltness of the water is the cause of the transformations of

Artemia, or that the degree of temperature determines the color and

marks of the wings which a certain chrysalis will assume on becoming a

butterfly, is the word "cause" used in the first sense? Obviously not:

causality has here an intermediary sense between those of unwinding and

releasing. Such, indeed, seems to be Eimer's own meaning when he speaks

of the "kaleidoscopic" character of the variation,[33] or when he says

that the variation of organized matter works in a definite way, just as

inorganic matter crystallizes in definite directions.[34] And it may be

granted, perhaps, that the process is a merely physical and chemical one

in the case of the color-changes of the skin. But if this sort of

explanation is extended to the case of the gradual formation of the eye

of the vertebrate, for instance, it must be supposed that the

physico-chemistry of living bodies is such that the influence of light

has caused the organism to construct a progressive series of visual

apparatus, all extremely complex, yet all capable of seeing, and of

seeing better and better.[35] What more could the most confirmed

finalist say, in order to mark out so exceptional a physico-chemistry?

And will not the position of a mechanistic philosophy become still more

difficult, when it is pointed out to it that the egg of a mollusc cannot

have the same chemical composition as that of a vertebrate, that the

organic substance which evolved toward the first of these two forms

could not have been chemically identical with that of the substance

which went in the other direction, and that, nevertheless, under the

influence of light, the same organ has been constructed in the one case

as in the other?

The more we reflect upon it, the more we shall see that this production

of the same effect by two different accumulations of an enormous number

of small causes is contrary to the principles of mechanistic philosophy.

We have concentrated the full force of our discussion upon an example

drawn from phylogenesis. But ontogenesis would have furnished us with

facts no less cogent. Every moment, right before our eyes, nature

arrives at identical results, in sometimes neighboring species, by

entirely different embryogenic processes. Observations of

"heteroblastia" have multiplied in late years,[36] and it has been

necessary to reject the almost classical theory of the specificity of

embryonic gills. Still keeping to our comparison between the eye of

vertebrates and that of molluscs, we may point out that the retina of

the vertebrate is produced by an expansion in the rudimentary brain of

the young embryo. It is a regular nervous centre which has moved toward

the periphery. In the mollusc, on the contrary, the retina is derived

from the ectoderm directly, and not indirectly by means of the embryonic

encephalon. Quite different, therefore, are the evolutionary processes

which lead, in man and in the Pecten, to the development of a like

retina. But, without going so far as to compare two organisms so distant

from each other, we might reach the same conclusion simply by looking at

certain very curious facts of regeneration in one and the same organism.

If the crystalline lens of a Triton be removed, it is regenerated by the

iris.[37] Now, the original lens was built out of the ectoderm, while

the iris is of mesodermic origin. What is more, in the _Salamandra

maculata_, if the lens be removed and the iris left, the regeneration of

the lens takes place at the upper part of the iris; but if this upper

part of the iris itself be taken away, the regeneration takes place in

the inner or retinal layer of the remaining region.[38] Thus, parts

differently situated, differently constituted, meant normally for

different functions, are capable of performing the same duties and even

of manufacturing, when necessary, the same pieces of the machine. Here

we have, indeed, the same effect obtained by different combinations of

causes.

Whether we will or no, we must appeal to some inner directing principle

in order to account for this convergence of effects. Such convergence

does not appear possible in the Darwinian, and especially the

neo-Darwinian, theory of insensible accidental variations, nor in the

hypothesis of sudden accidental variations, nor even in the theory that

assigns definite directions to the evolution of the various organs by a

kind of mechanical composition of the external with the internal forces.

So we come to the only one of the present forms of evolution which

remains for us to mention, viz., neo-Lamarckism.

* * * * *

It is well known that Lamarck attributed to the living being the power

of varying by use or disuse of its organs, and also of passing on the

variation so acquired to its descendants. A certain number of biologists

hold a doctrine of this kind to-day. The variation that results in a new

species is not, they believe, merely an accidental variation inherent in

the germ itself, nor is it governed by a determinism _sui generis_ which

develops definite characters in a definite direction, apart from every

consideration of utility. It springs from the very effort of the living

being to adapt itself to the circumstances of its existence. The effort

may indeed be only the mechanical exercise of certain organs,

mechanically elicited by the pressure of external circumstances. But it

may also imply consciousness and will, and it is in this sense that it

appears to be understood by one of the most eminent representatives of

the doctrine, the American naturalist Cope.[39] Neo-Lamarckism is

therefore, of all the later forms of evolutionism, the only one capable

of admitting an internal and psychological principle of development,

although it is not bound to do so. And it is also the only evolutionism

that seems to us to account for the building up of identical complex

organs on independent lines of development. For it is quite conceivable

that the same effort to turn the same circumstances to good account

might have the same result, especially if the problem put by the

circumstances is such as to admit of only one solution. But the question

remains, whether the term "effort" must not then be taken in a deeper

sense, a sense even more psychological than any neo-Lamarckian supposes.

For a mere variation of size is one thing, and a change of form is

another. That an organ can be strengthened and grow by exercise, nobody

will deny. But it is a long way from that to the progressive development

of an eye like that of the molluscs and of the vertebrates. If this

development be ascribed to the influence of light, long continued but

passively received, we fall back on the theory we have just criticized.

If, on the other hand, an internal activity is appealed to, then it must

be something quite different from what we usually call an effort, for

never has an effort been known to produce the slightest complication of

an organ, and yet an enormous number of complications, all admirably

coördinated, have been necessary to pass from the pigment-spot of the

Infusorian to the eye of the vertebrate. But, even if we accept this

notion of the evolutionary process in the case of animals, how can we

apply it to plants? Here, variations of form do not seem to imply, nor

always to lead to, functional changes; and even if the cause of the

variation is of a psychological nature, we can hardly call it an effort,

unless we give a very unusual extension to the meaning of the word. The

truth is, it is necessary to dig beneath the effort itself and look for

a deeper cause.

This is especially necessary, we believe, if we wish to get at a cause

of regular hereditary variations. We are not going to enter here into

the controversies over the transmissibility of acquired characters;

still less do we wish to take too definite a side on this question,

which is not within our province. But we cannot remain completely

indifferent to it. Nowhere is it clearer that philosophers can not

to-day content themselves with vague generalities, but must follow the

scientists in experimental detail and discuss the results with them. If

Spencer had begun by putting to himself the question of the

hereditability of acquired characters, his evolutionism would no doubt

have taken an altogether different form. If (as seems probable to us) a

habit contracted by the individual were transmitted to its descendants

only in very exceptional cases, all the Spencerian psychology would need

remaking, and a large part of Spencer's philosophy would fall to pieces.

Let us say, then, how the problem seems to us to present itself, and in

what direction an attempt might be made to solve it.

After having been affirmed as a dogma, the transmissibility of acquired

characters has been no less dogmatically denied, for reasons drawn _a

priori_ from the supposed nature of germinal cells. It is well known how

Weismann was led, by his hypothesis of the continuity of the germ-plasm,

to regard the germinal cells--ova and spermatozoa--as almost independent

of the somatic cells. Starting from this, it has been claimed, and is

still claimed by many, that the hereditary transmission of an acquired

character is inconceivable. But if, perchance, experiment should show

that acquired characters are transmissible, it would prove thereby that

the germ-plasm is not so independent of the somatic envelope as has been

contended, and the transmissibility of acquired characters would become

_ipso facto_ conceivable; which amounts to saying that conceivability

and inconceivability have nothing to do with the case, and that

experience alone must settle the matter. But it is just here that the

difficulty begins. The acquired characters we are speaking of are

generally habits or the effects of habit, and at the root of most habits

there is a natural disposition. So that one can always ask whether it is

really the habit acquired by the soma of the individual that is

transmitted, or whether it is not rather a natural aptitude, which

existed prior to the habit. This aptitude would have remained inherent

in the germ-plasm which the individual bears within him, as it was in

the individual himself and consequently in the germ whence he sprang.

Thus, for instance, there is no proof that the mole has become blind

because it has formed the habit of living underground; it is perhaps

because its eyes were becoming atrophied that it condemned itself to a

life underground.[40] If this is the case, the tendency to lose the

power of vision has been transmitted from germ to germ without anything

being acquired or lost by the soma of the mole itself. From the fact

that the son of a fencing-master has become a good fencer much more

quickly than his father, we cannot infer that the habit of the parent

has been transmitted to the child; for certain natural dispositions in

course of growth may have passed from the plasma engendering the father

to the plasma engendering the son, may have grown on the way by the

effect of the primitive impetus, and thus assured to the son a greater

suppleness than the father had, without troubling, so to speak, about

what the father did. So of many examples drawn from the progressive

domestication of animals: it is hard to say whether it is the acquired

habit that is transmitted or only a certain natural tendency--that,

indeed, which has caused such and such a particular species or certain

of its representatives to be specially chosen for domestication. The

truth is, when every doubtful case, every fact open to more than one

interpretation, has been eliminated, there remains hardly a single

unquestionable example of acquired and transmitted peculiarities, beyond

the famous experiments of Brown-Séquard, repeated and confirmed by other

physiologists.[41] By cutting the spinal cord or the sciatic nerve of

guinea-pigs, Brown-Séquard brought about an epileptic state which was

transmitted to the descendants. Lesions of the same sciatic nerve, of

the restiform body, etc., provoked various troubles in the guinea-pig

which its progeny inherited sometimes in a quite different form:

exophthalmia, loss of toes, etc. But it is not demonstrated that in

these different cases of hereditary transmission there had been a real

influence of the soma of the animal on its germ-plasm. Weismann at once

objected that the operations of Brown-Séquard might have introduced

certain special microbes into the body of the guinea-pig, which had

found their means of nutrition in the nervous tissues and transmitted

the malady by penetrating into the sexual elements.[42] This objection

has been answered by Brown-Séquard himself;[43] but a more plausible

one might be raised. Some experiments of Voisin and Peron have shown

that fits of epilepsy are followed by the elimination of a toxic body

which, when injected into animals,[44] is capable of producing

convulsive symptoms. Perhaps the trophic disorders following the nerve

lesions made by Brown-Séquard correspond to the formation of precisely

this convulsion-causing poison. If so, the toxin passed from the

guinea-pig to its spermatozoon or ovum, and caused in the development of

the embryo a general disturbance, which, however, had no visible effects

except at one point or another of the organism when developed. In that

case, what occurred would have been somewhat the same as in the

experiments of Charrin, Delamare, and Moussu, where guinea-pigs in

gestation, whose liver or kidney was injured, transmitted the lesion to

their progeny, simply because the injury to the mother's organ had given

rise to specific "cytotoxins" which acted on the corresponding organ of

the foetus.[45] It is true that, in these experiments, as in a former

observation of the same physiologists,[46] it was the already formed

foetus that was influenced by the toxins. But other researches of

Charrin have resulted in showing that the same effect may be produced,

by an analogous process, on the spermatozoa and the ova.[47] To

conclude, then: the inheritance of an acquired peculiarity in the

experiments of Brown-Séquard can be explained by the effect of a toxin

on the germ. The lesion, however well localized it seems, is transmitted

by the same process as, for instance, the taint of alcoholism. But may

it not be the same in the case of every acquired peculiarity that has

become hereditary?

There is, indeed, one point on which both those who affirm and those who

deny the transmissibility of acquired characters are agreed, namely,

that certain influences, such as that of alcohol, can affect at the same

time both the living being and the germ-plasm it contains. In such case,

there is inheritance of a defect, and the result is _as if_ the soma of

the parent had acted on the germ-plasm, although in reality soma and

plasma have simply both suffered the action of the same cause. Now,

suppose that the soma can influence the germ-plasm, as those believe who

hold that acquired characters are transmissible. Is not the most natural

hypothesis to suppose that things happen in this second case as in the

first, and that the direct effect of the influence of the soma is a

_general_ alteration of the germ-plasm? If this is the case, it is by

exception, and in some sort by accident, that the modification of the

descendant is the same as that of the parent. It is like the

hereditability of the alcoholic taint: it passes from father to

children, but it may take a different form in each child, and in none of

them be like what it was in the father. Let the letter C represent the

change in the plasm, C being either positive or negative, that is to

say, showing either the gain or loss of certain substances. The effect

will not be an exact reproduction of the cause, nor will the change in

the germ-plasm, provoked by a certain modification of a certain part of

the soma, determine a similar modification of the corresponding part of

the new organism in process of formation, unless all the other nascent

parts of this organism enjoy a kind of immunity as regards C: the same

part will then undergo alteration in the new organism, because it

happens that the development of this part is alone subject to the new

influence. And, even then, the part might be altered in an entirely

different way from that in which the corresponding part was altered in

the generating organism.

We should propose, then, to introduce a distinction between the

hereditability of _deviation_ and that of _character_. An individual

which acquires a new character thereby _deviates_ from the form it

previously had, which form the germs, or oftener the half-germs, it

contains would have reproduced in their development. If this

modification does not involve the production of substances capable of

changing the germ-plasm, or does not so affect nutrition as to deprive

the germ-plasm of certain of its elements, it will have no effect on the

offspring of the individual. This is probably the case as a rule. If, on

the contrary, it has some effect, this is likely to be due to a chemical

change which it has induced in the germ-plasm. This chemical change

might, by exception, bring about the original modification again in the

organism which the germ is about to develop, but there are as many and

more chances that it will do something else. In this latter case, the

generated organism will perhaps deviate from the normal type _as much

as_ the generating organism, but it will do so _differently_. It will

have inherited deviation and not character. In general, therefore, the

habits formed by an individual have probably no echo in its offspring;

and when they have, the modification in the descendants may have no

visible likeness to the original one. Such, at least, is the hypothesis

which seems to us most likely. In any case, in default of proof to the

contrary, and so long as the decisive experiments called for by an

eminent biologist[48] have not been made, we must keep to the actual

results of observation. Now, even if we take the most favorable view of

the theory of the transmissibility of acquired characters, and assume

that the ostensible acquired character is not, in most cases, the more

or less tardy development of an innate character, facts show us that

hereditary transmission is the exception and not the rule. How, then,

shall we expect it to develop an organ such as the eye? When we think of

the enormous number of variations, all in the same direction, that we

must suppose to be accumulated before the passage from the pigment-spot

of the Infusorian to the eye of the mollusc and of the vertebrate is

possible, we do not see how heredity, as we observe it, could ever have

determined this piling-up of differences, even supposing that individual

efforts could have produced each of them singly. That is to say that

neo-Lamarckism is no more able than any other form of evolutionism to

solve the problem.

* * * * *

In thus submitting the various present forms of evolutionism to a common

test, in showing that they all strike against the same insurmountable

difficulty, we have in no wise the intention of rejecting them

altogether. On the contrary, each of them, being supported by a

considerable number of facts, must be true in its way. Each of them must

correspond to a certain aspect of the process of evolution. Perhaps even

it is necessary that a theory should restrict itself exclusively to a

particular point of view, in order to remain scientific, _i.e._ to give

a precise direction to researches into detail. But the reality of which

each of these theories takes a partial view must transcend them all. And

this reality is the special object of philosophy, which is not

constrained to scientific precision because it contemplates no

practical application. Let us therefore indicate in a word or two the

positive contribution that each of the three present forms of

evolutionism seems to us to make toward the solution of the problem,

what each of them leaves out, and on what point this threefold effort

should, in our opinion, converge in order to obtain a more

comprehensive, although thereby of necessity a less definite, idea of

the evolutionary process.

The neo-Darwinians are probably right, we believe, when they teach that

the essential causes of variation are the differences inherent in the

germ borne by the individual, and not the experiences or behavior of the

individual in the course of his career. Where we fail to follow these

biologists, is in regarding the differences inherent in the germ as

purely accidental and individual. We cannot help believing that these

differences are the development of an impulsion which passes from germ

to germ across the individuals, that they are therefore not pure

accidents, and that they might well appear at the same time, in the same

form, in all the representatives of the same species, or at least in a

certain number of them. Already, in fact, the theory of _mutations_ is

modifying Darwinism profoundly on this point. It asserts that at a given

moment, after a long period, the entire species is beset with a tendency

to change. The _tendency to change_, therefore, is not accidental. True,

the change itself would be accidental, since the mutation works,

according to De Vries, in different directions in the different

representatives of the species. But, first we must see if the theory is

confirmed by many other vegetable species (De Vries has verified it only

by the _OEnothera Lamarckiana_),[49] and then there is the

possibility, as we shall explain further on, that the part played by

chance is much greater in the variation of plants than in that of

animals, because, in the vegetable world, function does not depend so

strictly on form. Be that as it may, the neo-Darwinians are inclined to

admit that the periods of mutation are determinate. The direction of the

mutation may therefore be so as well, at least in animals, and to the

extent we shall have to indicate.

We thus arrive at a hypothesis like Eimer's, according to which the

variations of different characters continue from generation to

generation in definite directions. This hypothesis seems plausible to

us, within the limits in which Eimer himself retains it. Of course, the

evolution of the organic world cannot be predetermined as a whole. We

claim, on the contrary, that the spontaneity of life is manifested by a

continual creation of new forms succeeding others. But this

indetermination cannot be complete; it must leave a certain part to

determination. An organ like the eye, for example, must have been formed

by just a continual changing in a definite direction. Indeed, we do not

see how otherwise to explain the likeness of structure of the eye in

species that have not the same history. Where we differ from Eimer is in

his claim that combinations of physical and chemical causes are enough

to secure the result. We have tried to prove, on the contrary, by the

example of the eye, that if there is "orthogenesis" here, a

psychological cause intervenes.

Certain neo-Lamarckians do indeed resort to a cause of a psychological

nature. There, to our thinking, is one of the most solid positions of

neo-Lamarckism. But if this cause is nothing but the conscious effort of

the individual, it cannot operate in more than a restricted number of

cases--at most in the animal world, and not at all in the vegetable

kingdom. Even in animals, it will act only on points which are under the

direct or indirect control of the will. And even where it does act, it

is not clear how it could compass a change so profound as an increase of

complexity: at most this would be conceivable if the acquired characters

were regularly transmitted so as to be added together; but this

transmission seems to be the exception rather than the rule. A

hereditary change in a definite direction, which continues to accumulate

and add to itself so as to build up a more and more complex machine,

must certainly be related to some sort of effort, but to an effort of

far greater depth than the individual effort, far more independent of

circumstances, an effort common to most representatives of the same

species, inherent in the germs they bear rather than in their substance

alone, an effort thereby assured of being passed on to their

descendants.

* * * * *

So we come back, by a somewhat roundabout way, to the idea we started

from, that of an _original impetus_ of life, passing from one generation

of germs to the following generation of germs through the developed

organisms which bridge the interval between the generations. This

impetus, sustained right along the lines of evolution among which it

gets divided, is the fundamental cause of variations, at least of those

that are regularly passed on, that accumulate and create new species. In

general, when species have begun to diverge from a common stock, they

accentuate their divergence as they progress in their evolution. Yet, in

certain definite points, they may evolve identically; in fact, they must

do so if the hypothesis of a common impetus be accepted. This is just

what we shall have to show now in a more precise way, by the same

example we have chosen, the formation of the eye in molluscs and

vertebrates. The idea of an "original impetus," moreover, will thus be

made clearer.

Two points are equally striking in an organ like the eye: the complexity

of its structure and the simplicity of its function. The eye is composed

of distinct parts, such as the sclerotic, the cornea, the retina, the

crystalline lens, etc. In each of these parts the detail is infinite.

The retina alone comprises three layers of nervous elements--multipolar

cells, bipolar cells, visual cells--each of which has its individuality

and is undoubtedly a very complicated organism: so complicated, indeed,

is the retinal membrane in its intimate structure, that no simple

description can give an adequate idea of it. The mechanism of the eye

is, in short, composed of an infinity of mechanisms, all of extreme

complexity. Yet vision is one simple fact. As soon as the eye opens, the

visual act is effected. Just because the act is simple, the slightest

negligence on the part of nature in the building of the infinitely

complex machine would have made vision impossible. This contrast between

the complexity of the organ and the unity of the function is what gives

us pause.

A mechanistic theory is one which means to show us the gradual

building-up of the machine under the influence of external circumstances

intervening either directly by action on the tissues or indirectly by

the selection of better-adapted ones. But, whatever form this theory may

take, supposing it avails at all to explain the detail of the parts, it

throws no light on their correlation.

Then comes the doctrine of finality, which says that the parts have been

brought together on a preconceived plan with a view to a certain end. In

this it likens the labor of nature to that of the workman, who also

proceeds by the assemblage of parts with a view to the realization of an

idea or the imitation of a model. Mechanism, here, reproaches finalism

with its anthropomorphic character, and rightly. But it fails to see

that itself proceeds according to this method--somewhat mutilated! True,

it has got rid of the end pursued or the ideal model. But it also holds

that nature has worked like a human being by bringing parts together,

while a mere glance at the development of an embryo shows that life goes

to work in a very different way. _Life does not proceed by the

association and addition of elements, but by dissociation and division._

We must get beyond both points of view, both mechanism and finalism

being, at bottom, only standpoints to which the human mind has been led

by considering the work of man. But in what direction can we go beyond

them? We have said that in analyzing the structure of an organ, we can

go on decomposing for ever, although the function of the whole is a

simple thing. This contrast between the infinite complexity of the organ

and the extreme simplicity of the function is what should open our eyes.

In general, when the same object appears in one aspect and in another as

infinitely complex, the two aspects have by no means the same

importance, or rather the same degree of reality. In such cases, the

simplicity belongs to the object itself, and the infinite complexity to

the views we take in turning around it, to the symbols by which our

senses or intellect represent it to us, or, more generally, to elements

_of a different order_, with which we try to imitate it artificially,

but with which it remains incommensurable, being of a different nature.

An artist of genius has painted a figure on his canvas. We can imitate

his picture with many-colored squares of mosaic. And we shall reproduce

the curves and shades of the model so much the better as our squares are

smaller, more numerous and more varied in tone. But an infinity of

elements infinitely small, presenting an infinity of shades, would be

necessary to obtain the exact equivalent of the figure that the artist

has conceived as a simple thing, which he has wished to transport as a

whole to the canvas, and which is the more complete the more it strikes

us as the projection of an indivisible intuition. Now, suppose our eyes

so made that they cannot help seeing in the work of the master a mosaic

effect. Or suppose our intellect so made that it cannot explain the

appearance of the figure on the canvas except as a work of mosaic. We

should then be able to speak simply of a collection of little squares,

and we should be under the mechanistic hypothesis. We might add that,

beside the materiality of the collection, there must be a plan on which

the artist worked; and then we should be expressing ourselves as

finalists. But in neither case should we have got at the real process,

for there are no squares brought together. It is the picture, _i.e._ the

simple act, projected on the canvas, which, by the mere fact of entering

into our perception, is _de_composed before our eyes into thousands and

thousands of little squares which present, as _re_composed, a wonderful

arrangement. So the eye, with its marvelous complexity of structure, may

be only the simple act of vision, divided _for us_ into a mosaic of

cells, whose order seems marvelous to us because we have conceived the

whole as an assemblage.

If I raise my hand from A to B, this movement appears to me under two

aspects at once. Felt from within, it is a simple, indivisible act.

Perceived from without, it is the course of a certain curve, AB. In this

curve I can distinguish as many positions as I please, and the line

itself might be defined as a certain mutual coördination of these

positions. But the positions, infinite in number, and the order in which

they are connected, have sprung automatically from the indivisible act

by which my hand has gone from A to B. Mechanism, here, would consist

in seeing only the positions. Finalism would take their order into

account. But both mechanism and finalism would leave on one side the

movement, which is reality itself. In one sense, the movement is _more_

than the positions and than their order; for it is sufficient to make it

in its indivisible simplicity to secure that the infinity of the

successive positions as also their order be given at once--with

something else which is neither order nor position but which is

essential, the mobility. But, in another sense, the movement is _less_

than the series of positions and their connecting order; for, to arrange

points in a certain order, it is necessary first to conceive the order

and then to realize it with points, there must be the work of assemblage

and there must be intelligence, whereas the simple movement of the hand

contains nothing of either. It is not intelligent, in the human sense of

the word, and it is not an assemblage, for it is not made up of

elements. Just so with the relation of the eye to vision. There is in

vision _more_ than the component cells of the eye and their mutual

coördination: in this sense, neither mechanism nor finalism go far

enough. But, in another sense, mechanism and finalism both go too far,

for they attribute to Nature the most formidable of the labors of

Hercules in holding that she has exalted to the simple act of vision an

infinity of infinitely complex elements, whereas Nature has had no more

trouble in making an eye than I have in lifting my hand. Nature's simple

act has divided itself automatically into an infinity of elements which

are then found to be coördinated to one idea, just as the movement of my

hand has dropped an infinity of points which are then found to satisfy

one equation.

We find it very hard to see things in that light, because we cannot

help conceiving organization as manufacturing. But it is one thing to

manufacture, and quite another to organize. Manufacturing is peculiar to

man. It consists in assembling parts of matter which we have cut out in

such manner that we can fit them together and obtain from them a common

action. The parts are arranged, so to speak, around the action as an

ideal centre. To manufacture, therefore, is to work from the periphery

to the centre, or, as the philosophers say, from the many to the one.

Organization, on the contrary, works from the centre to the periphery.

It begins in a point that is almost a mathematical point, and spreads

around this point by concentric waves which go on enlarging. The work of

manufacturing is the more effective, the greater the quantity of matter

dealt with. It proceeds by concentration and compression. The organizing

act, on the contrary, has something explosive about it: it needs at the

beginning the smallest possible place, a minimum of matter, as if the

organizing forces only entered space reluctantly. The spermatozoon,

which sets in motion the evolutionary process of the embryonic life, is

one of the smallest cells of the organism; and it is only a small part

of the spermatozoon which really takes part in the operation.

But these are only superficial differences. Digging beneath them, we

think, a deeper difference would be found.

A manufactured thing delineates exactly the form of the work of

manufacturing it. I mean that the manufacturer finds in his product

exactly what he has put into it. If he is going to make a machine, he

cuts out its pieces one by one and then puts them together: the machine,

when made, will show both the pieces and their assemblage. The whole of

the result represents the whole of the work; and to each part of the

work corresponds a part of the result.

Now I recognize that positive science can and should proceed as if

organization was like making a machine. Only so will it have any hold on

organized bodies. For its object is not to show us the essence of

things, but to furnish us with the best means of acting on them. Physics

and chemistry are well advanced sciences, and living matter lends itself

to our action only so far as we can treat it by the processes of our

physics and chemistry. Organization can therefore only be studied

scientifically if the organized body has first been likened to a

machine. The cells will be the pieces of the machine, the organism their

assemblage, and the elementary labors which have organized the parts

will be regarded as the real elements of the labor which has organized

the whole. This is the standpoint of science. Quite different, in our

opinion, is that of philosophy.

For us, the whole of an organized machine may, strictly speaking,

represent the whole of the organizing work (this is, however, only

approximately true), yet the parts of the machine do not correspond to

parts of the work, because _the materiality of this machine does not

represent a sum of means employed, but a sum of obstacles avoided_: it

is a negation rather than a positive reality. So, as we have shown in a

former study, vision is a power which should attain _by right_ an

infinity of things inaccessible to our eyes. But such a vision would not

be continued into action; it might suit a phantom, but not a living

being. The vision of a living being is an _effective_ vision, limited to

objects on which the being can act: it is a vision that is _canalized_,

and the visual apparatus simply symbolizes the work of canalizing.

Therefore the creation of the visual apparatus is no more explained by

the assembling of its anatomic elements than the digging of a canal

could be explained by the heaping up of the earth which might have

formed its banks. A mechanistic theory would maintain that the earth

had been brought cart-load by cart-load; finalism would add that it had

not been dumped down at random, that the carters had followed a plan.

But both theories would be mistaken, for the canal has been made in

another way.

With greater precision, we may compare the process by which nature

constructs an eye to the simple act by which we raise the hand. But we

supposed at first that the hand met with no resistance. Let us now

imagine that, instead of moving in air, the hand has to pass through

iron filings which are compressed and offer resistance to it in

proportion as it goes forward. At a certain moment the hand will have

exhausted its effort, and, at this very moment, the filings will be

massed and coördinated in a certain definite form, to wit, that of the

hand that is stopped and of a part of the arm. Now, suppose that the

hand and arm are invisible. Lookers-on will seek the reason of the

arrangement in the filings themselves and in forces within the mass.

Some will account for the position of each filing by the action exerted

upon it by the neighboring filings: these are the mechanists. Others

will prefer to think that a plan of the whole has presided over the

detail of these elementary actions: they are the finalists. But the

truth is that there has been merely one indivisible act, that of the

hand passing through the filings: the inexhaustible detail of the

movement of the grains, as well as the order of their final arrangement,

expresses negatively, in a way, this undivided movement, being the

unitary form of a resistance, and not a synthesis of positive elementary

actions. For this reason, if the arrangement of the grains is termed an

"effect" and the movement of the hand a "cause," it may indeed be said

that the whole of the effect is explained by the whole of the cause, but

to parts of the cause parts of the effect will in no wise correspond.

In other words, neither mechanism nor finalism will here be in place,

and we must resort to an explanation of a different kind. Now, in the

hypothesis we propose, the relation of vision to the visual apparatus

would be very nearly that of the hand to the iron filings that follow,

canalize and limit its motion.

The greater the effort of the hand, the farther it will go into the

filings. But at whatever point it stops, instantaneously and

automatically the filings coördinate and find their equilibrium. So with

vision and its organ. According as the undivided act constituting vision

advances more or less, the materiality of the organ is made of a more or

less considerable number of mutually coördinated elements, but the order

is necessarily complete and perfect. It could not be partial, because,

once again, the real process which gives rise to it has no parts. That

is what neither mechanism nor finalism takes into account, and it is

what we also fail to consider when we wonder at the marvelous structure

of an instrument such as the eye. At the bottom of our wondering is

always this idea, that it would have been possible for _a part only_ of

this coördination to have been realized, that the complete realization

is a kind of special favor. This favor the finalists consider as

dispensed to them all at once, by the final cause; the mechanists claim

to obtain it little by little, by the effect of natural selection; but

both see something positive in this coördination, and consequently

something fractionable in its cause,--something which admits of every

possible degree of achievement. In reality, the cause, though more or

less intense, cannot produce its effect except in one piece, and

completely finished. According as it goes further and further in the

direction of vision, it gives the simple pigmentary masses of a lower

organism, or the rudimentary eye of a Serpula, or the slightly

differentiated eye of the Alciope, or the marvelously perfected eye of

the bird; but all these organs, unequal as is their complexity,

necessarily present an equal coördination. For this reason, no matter

how distant two animal species may be from each other, if the progress

toward vision has gone equally far in both, there is the same visual

organ in each case, for the form of the organ only expresses the degree

in which the exercise of the function has been obtained.

But, in speaking of a progress toward vision, are we not coming back to

the old notion of finality? It would be so, undoubtedly, if this

progress required the conscious or unconscious idea of an end to be

attained. But it is really effected in virtue of the original impetus of

life; it is implied in this movement itself, and that is just why it is

found in independent lines of evolution. If now we are asked why and how

it is implied therein, we reply that life is, more than anything else, a

tendency to act on inert matter. The direction of this action is not

predetermined; hence the unforeseeable variety of forms which life, in

evolving, sows along its path. But this action always presents, to some

extent, the character of contingency; it implies at least a rudiment of

choice. Now a choice involves the anticipatory idea of several possible

actions. Possibilities of action must therefore be marked out for the

living being before the action itself. Visual perception is nothing

else:[50] the visible outlines of bodies are the design of our eventual

action on them. Vision will be found, therefore, in different degrees in

the most diverse animals, and it will appear in the same complexity of

structure wherever it has reached the same degree of intensity.

We have dwelt on these resemblances of structure in general, and on the

example of the eye in particular, because we had to define our attitude

toward mechanism on the one hand and finalism on the other. It remains

for us to describe it more precisely in itself. This we shall now do by

showing the divergent results of evolution not as presenting analogies,

but as themselves mutually complementary.

FOOTNOTES:

[Footnote 3: _Matière et mémoire_, Paris, 1896, chaps. ii. and iii.]

[Footnote 4: Calkins, _Studies on the Life History of Protozoa (Archiv

f. Entwicklungsmechanik_, vol. xv., 1903, pp. 139-186).]

[Footnote 5: Sedgwick Minot, _On Certain Phenomena of Growing Old_

(_Proc. Amer. Assoc. for the Advancement of Science_, 39th Meeting,

Salem, 1891, pp. 271-288).]

[Footnote 6: Le Dantec, _L'Individualité et l'erreur individualiste_,

Paris, 1905, pp. 84 ff.]

[Footnote 7: Metchnikoff, _La Dégénérescence sénile_ (_Année

biologique_, iii., 1897, pp. 249 ff.). Cf. by the same author, _La

Nature humaine_, Paris, 1903, pp. 312 ff.]

[Footnote 8: Roule, _L'Embryologie générale_, Paris, 1893, p. 319.]

[Footnote 9: The irreversibility of the series of living beings has been

well set forth by Baldwin (_Development and Evolution_, New York, 1902;

in particular p. 327).]

[Footnote 10: We have dwelt on this point and tried to make it clear in

the _Essai sur les données immédiates de la conscience_, pp. 140-151.]

[Footnote 11: In his fine work on _Genius in Art_ (_Le Génie dans

l'art_), M. Séailles develops this twofold thesis, that art is a

continuation of nature and that life is creation. We should willingly

accept the second formula; but by creation must we understand, as the

author does, a _synthesis_ of elements? Where the elements pre-exist,

the synthesis that will be made is virtually given, being only one of

the possible arrangements. This arrangement a superhuman intellect could

have perceived in advance among all the possible ones that surround it.

We hold, on the contrary, that in the domain of life the elements have

no real and separate existence. They are manifold mental views of an

indivisible process. And for that reason there is radical contingency in

progress, incommensurability between what goes before and what

follows--in short, duration.]

[Footnote 12: Bütschli, _Untersuchungen über mikroskopische Schäume und

das Protoplasma_, Leipzig, 1892, First Part.]

[Footnote 13: Rhumbler, _Versuch einer mechanischen Erklärung der

indirekten Zell-und Kernteilung_ (_Roux's Archiv_, 1896).]

[Footnote 14: Berthold, _Studien über Protoplasmamechanik_, Leipzig,

1886, p. 102. Cf. the explanation proposed by Le Dantec, _Théorie

nouvelle de la vie_, Paris, 1896, p. 60.]

[Footnote 15: Cope, _The Primary Factors of Organic Evolution_, Chicago,

1896, pp. 475-484.]

[Footnote 16: Maupas, "Etude des infusoires ciliés" (_Arch. de zoologie

expérimentale_, 1883, pp. 47, 491, 518, 549, in particular). P. Vignon,

_Recherches de cytologie générale sur les épithéliums_, Paris, 1902, p.

655. A profound study of the motions of the Infusoria and a very

penetrating criticism of the idea of tropism have been made recently by

Jennings (_Contributions to the Study of the Behavior of Lower

Organisms_, Washington, 1904). The "type of behavior" of these lower

organisms, as Jennings defines it (pp. 237-252), is unquestionably of

the psychological order.]

[Footnote 17: E.B. Wilson, _The Cell in Development and Inheritance_,

New York, 1897, p. 330.]

[Footnote 18: Dastre, _La Vie et la mort_, p. 43.]

[Footnote 19: Laplace, _Introduction à la théorie analytique des

probabilités_ (_OEuvres complètes_, vol. vii., Paris, 1886, p. vi.).]

[Footnote 20: Du Bois-Reymond, _Über die Grenzen des Naturerkennens_,

Leipzig, 1892.]

[Footnote 21: There are really two lines to follow in contemporary

neo-vitalism: on the one hand, the assertion that pure mechanism is

insufficient, which assumes great authority when made by such scientists

as Driesch or Reinke, for example; and, on the other hand, the

hypotheses which this vitalism superposes on mechanism (the

"entelechies" of Driesch, and the "dominants" of Reinke, etc.). Of these

two parts, the former is perhaps the more interesting. See the admirable

studies of Driesch--_Die Lokalisation morphogenetischer Vorgänge_,

Leipzig, 1899; _Die organischen Regulationen_, Leipzig, 1901;

_Naturbegriffe und Natururteile_, Leipzig, 1904; _Der Vitalismus als

Geschichte und als Lehre_, Leipzig, 1905; and of Reinke--_Die Welt als

Tat_, Berlin, 1899; _Einleitung in die theoretische Biologie_, Berlin,

1901; _Philosophie der Botanik_, Leipzig, 1905.]

[Footnote 22: P. Guérin, _Les Connaissances actuelles sur la fécondation

chez les phanérogames_, Paris, 1904, pp. 144-148. Cf. Delage,

_L'Hérédité_, 2nd edition, 1903, pp. 140 ff.]

[Footnote 23: Möbius, _Beiträge zur Lehre von der Fortpflanzung der

Gewächse_, Jena, 1897, pp. 203-206 in particular. Cf. Hartog, "Sur les

phénomènes de reproduction" (_Année biologique_, 1895, pp. 707-709).]

[Footnote 24: Paul Janet, _Les Causes finales_, Paris, 1876, p. 83.]

[Footnote 25: _Ibid._ p. 80.]

[Footnote 26: Darwin, _Origin of Species_, chap. ii.]

[Footnote 27: Bateson, _Materials for the Study of Variation_, London,

1894, especially pp. 567 ff. Cf. Scott, "Variations and Mutations"

(_American Journal of Science_, Nov. 1894).]

[Footnote 28: De Vries, _Die Mutationstheorie_, Leipzig, 1901-1903. Cf.,

by the same author, _Species and Varieties_, Chicago, 1905.]

[Footnote 29: Darwin, _Origin of Species_, chap. vi.]

[Footnote 30: Darwin, _Origin of Species_, chap. i.]

[Footnote 31: On this homology of hair and teeth, see Brandt, "Über ...

eine mutmassliche Homologie der Haare und Zahne" (_Biol. Centralblatt_,

vol. xviii., 1898, especially pp. 262 ff.).]

[Footnote 32: It seems, from later observations, that the transformation

of Artemia is a more complex phenomenon than was first supposed. See on

this subject Samter and Heymons, "Die Variation bei Artemia Salina"

(_Anhang zu den Abhandlungen der k. preussischen Akad. der

Wissenschaften_, 1902).]

[Footnote 33: Eimer, _Orthogenesis der Schmetterlinge_, Leipzig, 1897,

p. 24. Cf. _Die Entstehung der Arten_, p. 53.]

[Footnote 34: Eimer, _Die Entstehung der Arten_, Jena, 1888, p. 25.]

[Footnote 35: _Ibid._ pp. 165 ff.]

[Footnote 36: Salensky, "Heteroblastie" (_Proc. of the Fourth

International Congress of Zoology_, London, 1899, pp. 111-118). Salensky

has coined this word to designate the cases in which organs that are

equivalent, but of different embryological origin, are formed at the

same points in animals related to each other.]

[Footnote 37: Wolff, "Die Regeneration der Urodelenlinse" (_Arch. f.

Entwicklungsmechanik_, i., 1895, pp. 380 ff.).]

[Footnote 38: Fischel, "Über die Regeneration der Linse" (_Anat.

Anzeiger_, xiv., 1898, pp. 373-380).]

[Footnote 39: Cope, _The Origin of the Fittest_, 1887; _The Primary

Factors of Organic Evolution_, 1896.]

[Footnote 40: Cuénot, "La Nouvelle Théorie transformiste" (_Revue

générale des sciences_, 1894). Cf. Morgan, _Evolution and Adaptation_,

London, 1903, p. 357.]

[Footnote 41: Brown-Séquard, "Nouvelles recherches sur l'épilepsie due à

certaines lésions de la moelle épiniéere et des nerfs rachidiens"

(_Arch. de physiologie_, vol. ii., 1866, pp. 211, 422, and 497).]

[Footnote 42: Weismann, _Aufsätze über Vererbung_, Jena, 1892, pp.

376-378, and also _Vorträge über Descendenztheorie_, Jena, 1902, vol.

ii., p. 76.]

[Footnote 43: Brown-Séquard, "Hérédité d'une affection due à une cause

accidentelle" (_Arch. de physiologie_, 1892, pp. 686 ff.).]

[Footnote 44: Voisin and Peron, "Recherches sur la toxicité urinaire

chez les épileptiques" (_Arch. de neurologie_, vol. xxiv., 1892, and

xxv., 1893. Cf. the work of Voisin, _L'Épilepsie_, Paris, 1897, pp.

125-133).]

[Footnote 45: Charrin, Delamare and Moussu, "Transmission expérimentale

aux descendants de lésions développées chez les ascendants" (_C.R. de

l'Acad. des sciences_, vol. cxxxv., 1902, p. 191). Cf. Morgan,

_Evolution and Adaptation_, p. 257, and Delage, _L'Hérédité_, 2nd

edition, p. 388.]

[Footnote 46: Charrin and Delamare, "Hérédité cellulaire" (_C.R. de

l'Acad. des sciences_, vol. cxxxiii., 1901, pp. 69-71).]

[Footnote 47: Charrin, "L'Hérédité pathologique" (_Revue générale des

sciences_, 15 janvier 1896).]

[Footnote 48: Giard, _Controverses transformistes_, Paris, 1904, p.

147.]

[Footnote 49: Some analogous facts, however, have been noted, all in the

vegetable world. See Blaringhem, "La Notion d'espèce et la théorie de la

mutation" (_Année psychologique_, vol. xii., 1906, pp. 95 ff.), and De

Vries, _Species and Varieties_, p. 655.]

[Footnote 50: See, on this subject, _Matière et mémoire_, chap. i.]