Chapter IV (1)

"Owing to the extreme multiplication of the small species, and
especially of the most imperfect animals, the multiplicity of
individuals might be prejudicial to the preservation of the species,
to that of the progress acquired in the improvement of the
organization--in a word, to the general order, if nature had not
taken precautions to keep this multiplication within due limits over
which she would never pass.

"Animals devour one another, except those which live only on plants;
but the latter are exposed to being devoured by the carnivorous
animals.

"We know that it is the strongest and the best armed which devour
the weaker, and that the larger kinds devour the smaller.
Nevertheless, the individuals of a single species rarely devour each
other: they war upon other races.[182]

"The multiplication of the small species of animals is so
considerable, and the renewals of their generations are so prompt,
that these small species would render the earth uninhabitable to the
others if nature had not set a limit to their prodigious
multiplication. But since they serve as prey for a multitude of
other animals, as the length of their life is very limited, and as
the lowering of the temperature kills them, their numbers are always
maintained in proper proportions for the preservation of their races
and that of others.

"As to the larger and stronger animals, they would be too dominant
and injure the preservation of other races if they should multiply
in too great proportions. But their races devouring each other, they
would only multiply slowly and in a small number at a time; this
would maintain in this respect the kind of equilibrium which should
exist.

"Finally, only man, considered separately from all which is
characteristic of him, seems capable of multiplying indefinitely,
because his intelligence and his resources secure him from seeing
his increase arrested by the voracity of any animals. He exercises
over them such a supremacy that, instead of fearing the larger and
stronger races of animals, he is thus rather capable of destroying
them, and he continually checks their increase.

"But nature has given him numerous passions, which, unfortunately,
developing with his intelligence, thus place a great obstacle to
the extreme multiplication of the individuals of his species.

"Indeed, it seems as if man had taken it upon himself unceasingly to
reduce the number of his fellow-creatures; for never, I do not
hesitate to say, will the earth be covered with the population that
it could maintain. Several of its habitable parts would always be
alternately very sparsely populated, although the time for these
alternate changes would be to us measureless.

"Thus by these wise precautions everything is preserved in the
established order; the changes and perpetual renewals which are
observable in this order are maintained within limits over which
they cannot pass; the races of living beings all subsist in spite of
their variations; the progress acquired in the improvement of the
organization is not lost; everything which appears to be disordered,
overturned, anomalous, reënters unceasingly into the general order,
and even coöperates with it; and especially and always the will of
the sublime Author of nature and of all existing things is
invariably executed" (pp. 98-101).

In the sixth chapter the author treats of the degradation and simplification of the structure from one end to the other of the animal series, proceeding, as he says, inversely to the general order of nature, from the compound to the more simple. Why he thus works out this idea of a general degradation is not very apparent, since it is out of tune with his views, so often elsewhere expressed, of a progressive evolution from the simple to the complex, and to his own classification of the animal kingdom, beginning as it does with the simplest forms and ending with man. Perhaps, however, he temporarily adopts the prevailing method of beginning with the highest forms in order to bring out clearly the successive steps in inferiority or degradation presented in descending the animal scale.

We will glean some passages of this chapter which bear on his theory of descent. Speaking of the different kinds of aquatic surroundings he remarks:

"In the first place it should be observed that in the waters
themselves she [Nature] presents considerably diversified
circumstances; the fresh waters, marine waters, calm or stagnant
waters, running waters or streams, the waters of warm climates,
those of cold regions, finally those which are shallow and those
which are very deep, offer many special circumstances, each of which
acts differently on the animals living in them. Now, in a degree
equal to the make-up of the organization, the races of animals which
are exposed to either of these circumstances have been submitted to
special influences and have been diversified by them."

He then, after referring to the general degradation of the Batrachians, touches upon the atrophy of legs which has taken place in the snakes:

"If we should consider as a result of _degradation_ the loss of legs
seen in the snakes, the _Ophidia_ should be regarded as constituting
the lowest order of reptiles; but it would be an error to admit this
consideration. Indeed, the serpents being animals which, in order to
hide themselves, have adopted the habit of gliding directly along
the ground, their body has lengthened very considerably and
disproportionately to its thickness. Now, elongated legs proving
disadvantageous to their necessity of gliding and hiding, very short
legs, being only four in number, since they are vertebrate animals,
would be incapable of moving their bodies. Thus the habits of these
animals have been the cause of the disappearance of their legs, and
yet the _batrachians_, which have them, offer a more degraded
organization, and are nearer the fishes" (p. 155).

Referring on the next page to the fishes, he remarks:--

"Without doubt their general form, their lack of a constriction
between the head and the body to form a neck, and the different fins
which support them in place of legs, are the results of the
influence of the dense medium which they inhabit, and not that of
the _dégradation_ of their organization. But this modification
(_dégradation_) is not less real and very great, as we can convince
ourselves by examining their internal organs; it is such as to
compel us to assign to the fishes a rank lower than that of the
reptiles."

He then states that the series from the lamprey and fishes to the mammals is not a regularly gradated one, and accounts for this "because the work of nature has been often changed, hindered, and diverted in direction by the influences which singularly different, even contrasted, circumstances have exercised on the animals which are there found exposed in the course of a long series of their renewed generations."

Lamarck thus accounts for the production of the radial symmetry of the medusæ and echinoderms, his _Radiaires_. At the present day this symmetry is attributed perhaps more correctly to their more or less fixed mode of life.

"It is without doubt by the result of this means which nature
employs, at first with a feeble energy with _polyps_, and then with
greater developments in the _Radiata_, that the radial form has been
acquired; because the subtile ambient fluids, penetrating by the
alimentary canal, and being expansive, have been able, by an
incessantly renewed repulsion from the centre towards every point of
the circumference, to give rise to this radiated arrangement of
parts.

"It is by this cause that, in the Radiata, the intestinal canal,
although still very imperfect, since more often it has only a single
opening, is yet complicated with numerous radiating vasculiform,
often ramified, appendages.

"It is, doubtless, also by this cause that in the soft Radiates, as
the medusæ, etc., we observe a constant isochronic movement,
movement very probably resulting from the successive intermissions
between the masses of subtile fluids which penetrate into the
interior of these animals and those of the same fluids which escape
from it, often being spread throughout all their parts.

"We cannot say that the isochronic movements of the soft Radiates
are the result of their respiration; for below the vertebrate
animals nature does not offer, in that of any animal, these
alternate and measured movements of inspiration and expiration.
Whatever may be the respiration of Radiates, it is extremely slow,
and is executed without perceptible movements" (p. 200).

_The Influence of Circumstances on the Actions and Habits of Animals._

It is in Chapter VII. that the views of Lamarck are more fully presented than elsewhere, and we therefore translate all of it as literally as possible, so as to preserve the exact sense of the author.

"We do not here have to do with a line of argument, but with the
examination of a positive fact, which is more general than is
supposed, and which has not received the attention it deserves,
doubtless because, very often, it is quite difficult to discover.
This fact consists in the influence which circumstances exert on the
different organisms subjected to them.

"In truth, for a long time there has been noticed the influence of
different states of our organization on our character, our
propensities (_penchants_), our actions, and even our ideas; but it
seems to me that no one has yet recognized that of our actions and
of our habits on our organization itself. Now, as these actions and
these habits entirely depend on the circumstances in which we
habitually find ourselves, I shall try to show how great is the
influence which these circumstances exercise on the general form, on
the condition of the parts, and even on the organization of living
bodies. It is therefore this very positive fact which is to be the
subject of this chapter.

"If we have not had numerous occasions to plainly recognize the
effects of this influence on certain organisms which we have
transported under entirely new and different circumstances, and if
we had not seen these effects and the changes resulting from them
produced, in a way, under our very eyes, the important fact in
question would have always remained unknown.

"The influence of circumstances is really continuously and
everywhere active on living beings, but what renders it difficult
for us to appreciate this influence is that its effects only become
sensible or recognizable (especially in the animals) at the end of a
long period.

"Before stating and examining the proofs of this fact, which
deserves our attention, and which is very important for a zoölogical
philosophy, let us resume the thread of the considerations we had
begun to discuss.

"In the preceding paragraph we have seen that it is now an
incontrovertible fact that, in considering the animal scale in a
sense the inverse of that of nature, we find that there exists in
the groups composing this scale a continuous but irregular
modification (_dégradation_) in the organization of animals which
they comprise, an increasing simplification in the organization of
these organisms; finally, a proportionate diminution in the number
of faculties of these beings.

"This fact once recognized may throw the greatest light on the very
order which nature has followed in the production of all the
existing animals; but it does not show why the structure of animals
in its increasing complexity from the more imperfect up to the most
perfect offers only an irregular gradation, whose extent presents a
number of anomalies or digressions which have no appearance of order
in their diversity.

"Now, in seeking for the reason of this singular irregularity in the
increasing complexity of organization of animals, if we should
consider the outcome of the influences that the infinitely
diversified circumstances in all parts of the globe exercise on the
general form, the parts, and the very organization of these animals,
everything will be clearly explained.

"It will, indeed, be evident that the condition in which we find all
animals is, on one side, the result of the increasing complexity of
the organization which tends to form a regular gradation, and, on
the other, that it is that of the influences of a multitude of very
different circumstances which continually tend to destroy the
regularity in the gradations of the increasing complexity of the
organization.

"Here it becomes necessary for me to explain the meaning I attach to
the expression _circumstances influencing the form and structure of
animals_--namely, that in becoming very different they change, with
time, both their form and organization by proportionate
modifications.

"Assuredly, if these expressions should be taken literally, I should
be accused of an error; for whatever may be the circumstances, they
do not directly cause any modification in the form and structure of
animals.

"But the great changes in the circumstances bring about in animals
great changes in their needs, and such changes in their needs
necessarily cause changes in their actions. Now, if the new needs
become constant or very permanent, the animals then assume new
_habits_, which are as durable as the needs which gave origin to
them. We see that this is easily demonstrated and even does not need
any explanation to make it clearer.

"It is then evident that a great change in circumstances having
become constant in a race of animals leads these animals into new
habits.

"Now, if new circumstances, having become permanent in a race of
animals, have given to these animals new _habits_--that is to say,
have led them to perform new actions which have become
habitual--there will from this result the use of such a part by
preference to that of another, and in certain cases the total lack
of use of any part which has become useless.

"Nothing of all this should be considered as a hypothesis or as a
mere peculiar opinion; they are, on the contrary, truths which
require, in order to be made evident, only attention to and the
observation of facts.

"We shall see presently by the citation of known facts which prove
it, on one side that the new wants, having rendered such a part
necessary, have really by the result of efforts given origin to this
part, and that as the result of its sustained use it has gradually
strengthened it, developed, and has ended in considerably increasing
its size; on the other side we shall see that, in certain cases, the
new circumstances and new wants having rendered such a part wholly
useless, the total lack of use of this part has led to the result
that it has gradually ceased to receive the development which the
other parts of the animal obtain; that it gradually becomes
emaciated and thin; and that finally, when this lack of use has been
total during a long time, the part in question ends in disappearing.
All this is a positive fact; I propose to give the most convincing
proofs.

"In the plants, where there are no movements, and, consequently, no
habits properly so called, great changes in circumstances do not
bring about less great differences in the development of their
parts; so that these differences originate and develop certain of
them, while they reduce and cause several others to disappear. But
here everything operates by the changes occurring in the nutrition
of the plant, in its absorptions and transpirations, in the amount
of heat, light, air, and humidity which it habitually receives;
finally, in the superiority that certain of the different vital
movements may assume over others.

"Between individuals of the same species, some of which are
constantly well nourished, and in circumstances favorable to their
entire development, while the others live under reversed
circumstances, there is brought about a difference in the condition
of these individuals which gradually becomes very remarkable. How
many examples could I not cite regarding animals and plants, which
would confirm the grounds for this view! Now, if the circumstances
remain the same, rendering habitual and constant the condition of
individuals badly fed, diseased, or languishing, their internal
organization becomes finally modified, and reproduction between the
individuals in question preserves the acquired modifications, and
ends in giving rise to a race very distinct from that of the
individuals which unceasingly meet with circumstances favorable to
their development.

"A very dry spring-time is the cause of the grass of a field growing
very slowly, remaining scraggy and puny, flowering and fruiting
without growing much.

"A spring interspersed with warm days and rainy days makes the same
grass grow rapidly, and the harvest of hay is then excellent.

"But if any cause perpetuates the unfavorable circumstances
surrounding these plants, they vary proportionally, at first in
their appearance and general condition, and finally in several
particulars of their characters.

"For example, if some seed of any of the grasses referred to should
be carried into an elevated place, on a dry and stony greensward
much exposed to the winds, and should germinate there, the plant
which should be able to live in this place would always be badly
nourished, and the individuals reproduced there continuing to exist
under these depressing circumstances, there would result a race
truly different from that living in the field, though originating
from it. The individuals of this new race would be small, scraggy,
and some of their organs, having developed more than others, would
then offer special proportions.

"Those who have observed much, and who have consulted the great
collections, have become convinced that in proportion as the
circumstances of habitat, exposure, climate, food, mode of life,
etc., come to change, the characters of size, form, proportion
between the parts, color, consistence, agility, and industry in the
animals change proportionally.

"What nature accomplishes after a long time, we bring about every
day by suddenly changing, in the case of a living plant, the
circumstances under which it and all the individuals of its species
exist.

"All botanists know that the plants which they transplant from their
birthplace into gardens for cultivation gradually undergo changes
which at last render them unrecognizable. Many plants naturally
very hairy then become glabrous, or almost so; many of those which
were creeping and trailing, then become erect; others lose their
spines or their prickles; others still, from the woody and perennial
condition which their stem possesses in a warm climate, pass, in our
climate, into an herbaceous condition, and among these several are
nothing more than annual plants; finally, the dimensions of their
parts themselves undergo very considerable changes. These effects of
changes of circumstances are so well known that botanists prefer not
to describe garden plants, at least only those which have been newly
cultivated.

"Is not cultivated wheat (_Triticum sativum_) only a plant brought
by man into the condition in which we actually see it? Who can tell
me in what country such a plant lives in a state of nature--that is
to say, without being there the result of its culture in some
neighboring region?

"Where occur in nature our cabbage, lettuce, etc., in the condition
in which we see them in our kitchen-gardens? Is it not the same as
regards a number of animals which domestication has changed or
considerably modified?

"What very different races among our fowls and domestic pigeons,
which we have obtained by raising them in different circumstances
and in different countries, and how vainly do we now endeavor to
rediscover them in nature!

"Those which are the least changed, without doubt by a more recent
process of domestication, and because they do not live in a climate
which is foreign to them, do not the less possess, in the condition
of some of their parts, great differences produced by the habits
which we have made them contract. Thus our ducks and our domestic
geese trace back their type to the wild ducks and geese; but ours
have lost the power of rising into the high regions of the air, and
of flying over extensive regions; finally, a decided change has
been wrought in the state of their parts compared with that of
animals of the race from which they have descended.

"Who does not know that such a native bird, which we raise in a cage
and which lives there five or six years in succession, and after
that replaced in nature--namely, set free--is then unable to fly
like its fellows which have always been free? The slight change of
circumstance operating on this individual has only diminished its
power of flight, and doubtless has not produced any change in the
shape of its parts. But if a numerous series of generations of
individuals of the same race should have been kept in captivity for
a considerable time, there is no doubt but that even the form of the
parts of these individuals would gradually undergo notable changes.
For a much stronger reason, if, instead of a simple captivity
constantly maintained over them, this circumstance had been at the
same time accompanied by a change to a very different climate, and
if these individuals by degrees had been habituated to other kinds
of food, and to other kinds of movements to obtain it; certainly
these circumstances, united and becoming constant, would insensibly
form a new and special race.

"Where do we find, in nature, this multitude of races of _dogs_,
which, as the result of domesticity to which we have reduced these
animals, have been brought into their present condition? Where do we
find these bull-dogs, greyhounds, water spaniels, spaniels,
pug-dogs, etc., etc., races which present among themselves much
greater differences than those which we admit to be specific in wild
animals of the same genus?

"Without doubt, a primitive single race, very near the wolf, if it
is not itself the true type, has been submitted by man, at some
period, to the process of domestication. This race, which then
offered no difference between its individuals, has been gradually
dispersed by man into different countries, with different climates;
and after a time these same individuals, having undergone the
influences of their habitats, and of the different habits they were
obliged to contract in each country, have undergone remarkable
changes, and have formed different special races. Now, the man who,
for commercial reasons or from interests of any other kind, travels
a very great distance, having carried into a densely populated
place, as for example a great capital, different races of dogs
originated in some very distant country, then the increase of these
races by heredity (_génération_) has given rise successively to all
those we now know.

"The following fact proves, as regards plants, how a change in any
important circumstance leads to a change in the parts of their
organisms.

"So long as _Ranunculus aquatilis_ is submerged in the water, its
leaves are all finely incised and the divisions hair-like; but when
the stalks of this plant reach the surface of the water, the leaves
which grow out in the air are wider, rounded, and simply lobed. If
some feet from the same plant the roots succeed in pushing into a
soil only damp, without being submerged, their stalks then are
short, none of their leaves are divided into capillary divisions,
which gives rise to _Ranunculus hederaceus_, which the botanists
regard as a species whenever they meet with it.

"There is no doubt that as regards animals important changes in the
circumstances under which they are accustomed to live do not produce
alteration in their organs; for here the changes are much slower in
operating than in plants, and, consequently, are to us less marked,
and their cause less recognizable.

"As to the circumstances which have so much power in modifying the
organs of living beings, the most influential are, doubtless, the
diversity of the surroundings in which they live; but besides this
there are many others which, in addition, have a considerable
influence in the production of the effects in question.

"It is known that different localities change in nature and quality
owing to their position, their nature, and their climate, as is
easily seen in passing over different places distinguished by
special features; hence we see a cause of variation for the animals
and plants which live in these different places. But what we do not
sufficiently know, and even what we generally refuse to believe, is
that each place itself changes with time in exposure, in climate, in
nature, and quality, although with a slowness so great in relation
to our own continuance that we attribute to it a perfect stability.

"Now, in either case, these changed localities proportionally change
the circumstances relative to the organisms which inhabit them, and
the latter then give rise to other influences bearing on these same
beings.

"We perceive from this that, if there are extremes in these changes,
there are also gradations--namely, degrees which are intermediate
and which fill the interval. Consequently there are also gradations
in the differences which distinguish what we call _species_.

"It is then evident that the whole surface of the earth offers, in
the nature and situation of the matters which occupy its different
points, a diversity of circumstances which is throughout in relation
with that of the forms and parts of animals, independent of the
special diversity which necessarily results from the progress of the
composition of organization in each animal.

"In each locality where animals can live, the circumstances which
establish there an order of things remain for a long time the same,
and really change there only with a slowness so great that man
cannot directly notice them. He is obliged to consult monuments to
recognize that in each one of these places the order of things that
he discovers there has not always been the same, and to perceive
that it will change more.

"The races of animals which live in each of these places should,
then, retain their customary habits there also for a long time;
hence to us seems an apparent constancy of races which we call
_species_--constancy which has originated among us the idea that
these races are as ancient as nature.

"But in the different points of the earth's surface which can be
inhabited, nature and the situation of the places and climates
constitute there, for the animals as for the plants, _different
circumstances_ of all sorts of degrees. The animals which inhabit
these different places should then differ from each other, not only
on account of the state of nature of the organization in each race,
but, besides, by reason of the habits that the individuals of each
race there are forced to have; so, in proportion as he traverses the
larger parts of the earth's surface the observing naturalist sees
circumstances changing in a manner somewhat noticeable; he
constantly sees that the species change proportionately in their
characters.

"Now, the true order of things necessary to consider in all this
consists in recognizing:

"1. That every slight change maintained under the circumstances
where occur each race of animals, brings about in them a real change
in their wants.

"2. That every change in the wants of animals necessitates in them
other movements (_actions_) to satisfy the new needs, and
consequently other habits.

"3. That every new want necessitating new actions to satisfy it,
demands of the animal which feels it both the more frequent use of
such of its parts of which before it made less use, which develops
and considerably enlarges them, and the use of new parts which
necessity has caused to insensibly develop in it by the effects of
its inner feelings; which I shall constantly prove by known facts.

"Thus, to arrive at a knowledge of the true causes of so many
different forms and so many different habits of which the known
animals offer us examples, it is necessary to consider that
circumstances infinitely diversified, but all slowly changing, into
which the animals of each race are successively thrown, have caused,
for each of them, new wants and necessarily changes in their habits.
Moreover, this truth, which cannot be denied, being once recognized,
it will be easy to see how the new needs have been able to be
satisfied, and the new habits formed, if any attention be given to
the two following laws of nature, which observation always confirms:

"_First Law._

"In every animal which has not exceeded the term of its development,
the more frequent and sustained use of any organ gradually
strengthens this organ, develops and enlarges it, and gives it a
strength proportioned to the length of time of such use; while the
constant lack of use of such an organ imperceptibly weakens it,
causes it to become reduced, progressively diminishes its faculties,
and ends in its disappearance.

"_Second Law._

"Everything which nature has caused individuals to acquire or lose
by the influence of the circumstances to which their race may be for
a long time exposed, and consequently by the influence of the
predominant use of such an organ, or by that of the constant lack of
use of such part, it preserves by heredity (_génération_) and passes
on to the new individuals which descend from it, provided that the
changes thus acquired are common to both sexes, or to those which
have given origin to these new individuals.

"These are the two fundamental truths which can be misunderstood
only by those who have never observed or followed nature in its
operations, or only by those who allow themselves to fall into the
error which I have combated.

"Naturalists having observed that the forms of the parts of animals
compared with the uses of these parts are always in perfect accord,
have thought that the forms and conditions of parts have caused the
function; but this is a mistake, for it is easy to demonstrate by
observation that it is, on the contrary, the needs and uses of
organs which have developed these same parts, which have even given
origin to them where they did not exist, and which consequently have
given rise to the condition in which we observe them in each animal.

"If this were not so, it would have been necessary for nature to
have created for the parts of animals as many forms as the diversity
of circumstances in which they have to live had required, and that
these forms and also the circumstances had never varied.

"This is certainly not the existing order of things, and if it were
really such, we should not have the race-horses of England; we
should not have our great draft horses, so clumsy and so different
from the first named, for nature herself has not produced their
like; we should not, for the same reason, have terrier dogs with bow
legs, greyhounds so swift in running, water-spaniels, etc.; we
should not have tailless fowls, fantail pigeons, etc.; finally, we
could cultivate the wild plants as much as we pleased in the rich
and fertile soil of our gardens without fearing to see them change
by long culture.

"For a long time we have felt the force of the saying which has
passed into the well-known proverb--_habits form a second nature_.

"Assuredly, if the habits and nature of each animal can never vary,
the proverb is false, has no foundation, and does not apply to the
instances which led to its being spoken.

"If we should seriously consider all that I have just stated, it
might be thought that I had good reason when in my work entitled
_Recherches sur les Corps vivans_ (p. 50) I established the
following proposition:

"'It is not the organs--that is to say, the nature and form of the
parts of the body of an animal--which have given rise to its habits
and its special faculties; but it is, on the contrary, its habits,
its manner of life, and the circumstances in which are placed the
individuals from which it originates, which have, with time, brought
about the form of its body, the number and condition of its organs,
finally, the faculties which it enjoys.'

"If we weigh this proposition, and if we recall all the observations
which nature and the state of things continually lead us to do, then
its importance and its solidity will become more evident.

"Time and favorable circumstances are, as I have already said, the
two principal means which nature employs to give existence to all
her productions: we know that time for her has no limits, and that
consequently it is ever at her disposal.

"As to the circumstances of which she has need, and which she uses
still daily to cause variations in all that she continues to
produce, we can say that they are, in some degree, for her
inexhaustible.

"The principal circumstances arise from the influence of climate;
from those of different temperatures of the atmosphere, and from all
the environing media; from that of the diversity of different
localities and their situation; from that of habits, the ordinary
movements, the most frequent actions; finally, from that of means of
preservation, of mode of living, of defence, of reproduction, etc.

"Moreover, owing to these diverse influences, the faculties increase
and become stronger by use, become differentiated by the new habits
preserved for long ages, and insensibly the organization, the
consistence--in a word, the nature and condition of parts, as also
of the organs--participate in the results of all these influences,
become preserved, and are propagated by generation.

"These truths, which are only the results of the two natural laws
above stated, are in every case completely confirmed by facts; they
clearly indicate the course of nature in all the diversity of its
products.

"But instead of contenting ourselves with generalities which might
be considered as hypothetical, let us directly examine the facts,
and consider, in the animals, the result of the use or disuse of
their organs on the organs themselves, according to the habits that
each race has been compelled to contract.

"I shall now attempt to prove that the constant lack of exercise of
organs at first diminishes their faculties, gradually impoverishes
them, and ends by making them disappear, or even causing them to be
atrophied, if this lack of use is perpetuated for a very long time
through successive generations of animals of the same race.

"I shall next prove that, on the contrary, the habit of exercising
an organ, in every animal which has not attained the limit of the
diminution of its faculties, not only perfects and increases the
faculties of this organ, but, besides, enables it to acquire
developments and dimensions which insensibly change it; so that with
time it renders it very different from the same organ in another
animal which exercises it much less.

"_The lack of use of an organ, become constant by the habits formed,
gradually impoverishes this organ, and ends by causing it to
disappear and even to destroy it._

"As such a proposition can only be admitted on proof, and not by its
simple announcement, let us prove it by the citation of the leading
known facts on which it is based.

"The vertebrate animals, whose plan of organization is in all nearly
the same, although they offer much diversity in their parts, have
jaws armed with _teeth_; moreover, those among them which
circumstances have placed in the habit of swallowing their food
without previous _mastication_ are exposed to the result that their
teeth become undeveloped. These teeth, then, either remain concealed
between the bony edges of the jaws, without appearing above, or even
their gums are found to have been atrophied.

"In the baleen whales, which have been supposed to be completely
deprived of teeth, M. Geoffroy has found them concealed in the jaws
of the _foetus_ of this animal. This professor has also found in
the birds the groove where the teeth should be situated; but they
are no longer to be seen there.

"In the class even of mammals, which comprises the most perfect
animals, and chiefly those in which the vertebrate plan of
organization is most perfectly carried out, not only the baleen has
no usable teeth, but the ant-eater (_Myrmecophaga_) is also in the
same condition, whose habit of not masticating its food has been for
a long time established and preserved in its race.

"The presence of eyes in the head is a characteristic of a great
number of different animals, and becomes an essential part of the
plan of organization of vertebrates.

"Nevertheless the mole, which owing to its habits makes very little
use of vision, has only very small eyes, which are scarcely visible,
since they exercise these organs to a very slight extent.

"The _Aspalax_ of Olivier (_Voyage en Egypte et en Perse_, ii.
pl. 28 f. 2), which lives under ground like the mole, and which
probably exposes itself still less than that animal to the light of
day, has totally lost the power of sight; also it possesses only
vestiges of the organ of which it is the seat; and yet these
vestiges are wholly concealed under the skin and other parts which
cover them, and do not permit the least access to the light.

"The _Proteus_, an aquatic reptile allied to the salamander in its
structure, and which lives in the dark subterranean waters of deep
caves, has, like the _Aspalax_, only vestiges of the organs of
sight--vestiges which are covered and concealed in the same manner.

"We turn to a decisive consideration relative to this question.

"Light does not penetrate everywhere; consequently animals which
habitually live in situations where it does not penetrate lack the
occasion of exercising the organs of sight, if nature has provided
them with them. Moreover, the animals which make part of the plan of
organization in which _eyes_ are necessarily present, have
originally had them. However, since we find them among those which
are deprived of the use of this organ, and which have only vestiges
concealed and covered over, it should be evident that the
impoverishment and even the disappearance of these organs are the
result of a constant lack of exercise.

"What proves it is that the organ of _hearing_ is never in this
condition, and that we always find it in the animals when the nature
of their organization should require its existence; the reason is as
follows.

"The _cause of sound_, that which, moved by the shock or the
vibrations of bodies, transmits to the organ of hearing the
impression which it receives, penetrates everywhere, traverses all
the media, and even the mass of the densest bodies: from this it
results that every animal which makes a part of a plan of
organization to which _hearing_ is essential, has always occasion to
exercise this organ in whatever situation it lives. So, among the
_vertebrate animals_ we see none deprived of their organs of
hearing; but in the groups below them, when the same organs are once
wanting, we do not again find them.

"It is not so with the organ of sight, for we see this organ
disappear, reappear, and again disappear, in proportion to the
possibility or impossibility of the animal's exercising it.

"In the _acephalous molluscs_, the great development of the mantle
of these molluscs has rendered their eyes and even their head
entirely useless. These organs, also forming a part of a plan of
organization which should comprise them, have disappeared and
atrophied from constant lack of use.

"Finally, it is a part of the plan of organization of _reptiles_, as
in other vertebrate animals, to have four legs appended to their
skeleton. The serpents should consequently have four, though they do
not form the lowest order of reptiles, and are not so near the
fishes as the batrachians (the frogs, the salamanders, etc.).

"However, the serpents having taken up the habit of gliding along
the ground, and of concealing themselves in the grass, their body,
owing to continually repeated efforts to elongate itself so as to
pass through narrow spaces, has acquired a considerable length
disproportionate to its size. Moreover, limbs would have been very
useless to these animals, and consequently would not have been
employed: because long legs would have interfered with their need of
gliding, and very short legs, not being more than four in number,
would have been incapable of moving their body. Hence the lack of
use of these parts having been constant in the races of these
animals, has caused the total disappearance of these same parts,
although really included in the plan of organization of the animals
of their class.

"Many insects which by the natural character of their order, and
even of their genus, should have wings, lack them more or less
completely from disuse. A quantity of Coleoptera, Orthoptera,
Hymenoptera, and of Hemiptera, etc., afford examples; the habits of
these animals do not require them to make use of their wings.

"But it is not sufficient to give the explanation of the cause which
has brought about the condition of the organs of different
animals--a condition which we see to be always the same in those of
the same species; we must besides observe the changes of condition
produced in the organs of one and the same individual during its
life, by the single result of a great change in the special habits
in the individuals of its species. The following fact, which is one
of the most remarkable, will serve to prove the influence of habits
on the condition of organs, and show how changes wrought in the
habits of an individual, produce the condition of the organs which
are brought into action during the exercise of these habits.

"M. Tenon, member of the Institute, has given an account to the
Class of Sciences, that having examined the intestinal canal of
several men who had been hard drinkers all their lives, he had
constantly found it to be shortened to an extraordinary extent,
compared with the same organ in those not given to such a habit.

"We know that hard drinkers, or those who are addicted to
drunkenness, take very little solid food, that they eat very
lightly, and that the beverage which they take in excess frequently
suffices to nourish them.

"Moreover, as fluid aliments, especially spirituous liquors, do not
remain a long time either in the stomach or in the intestines, the
stomach and the remainder of the intestinal canal lose the habit of
being distended in intemperate persons, so also in sedentary persons
and those engaged in mental labor, who are habituated to take but
little food. Gradually and at length their stomach becomes
contracted, and their intestines shortened.

"We are not concerned here with the shrinkage and shortening
produced by a puckering of the parts, which permit ordinary
extension, if instead of a continued emptiness these viscera should
be filled; the shrinkage and shortening in question are real,
considerable, and such that these organs would burst open rather
than yield suddenly to the causes which would require ordinary
extension.

"In circumstances of persons of the same age, compare a man who, in
order to devote himself to habitual study and mental work, which
have rendered his digestion more difficult, has contracted the habit
of eating lightly, with another who habitually takes a good deal of
exercise, walks out often, and eats heartily; the stomach of the
first will be weakened, and a small quantity of food will fill it,
while that of the second will be not only maintained in its ordinary
health but even strengthened.

"We have here the case of an organ much modified in its dimensions
and in its faculties by the single cause of a change in habits
during the life of the individual.

"_The frequent use of an organ become constant by habit increases
the faculties of this organ, even develops it, and enables it to
acquire dimensions and a power of action which it does not possess
in animals which exercise less._

"We have just said that the lack of employment of an organ which
necessarily exists modifies it, impoverishes it, and ends by its
disappearing entirely.

"I shall now demonstrate that the continued employment of an organ,
with the efforts made to draw out its powers under circumstances
where it would be of service, strengthens, extends, and enlarges
this organ, or creates a new one which can exercise the necessary
functions.

"The bird which necessity drives to the water to find there prey
fitted for its sustenance, opens the digits of its feet when it
wishes to strike the water and propel itself along its surface. The
skin which unites these digits at their base, by these acts of
spreading apart being unceasingly repeated contracts the habit of
extending; so that after a while the broad membranes which connect
the digits of ducks, geese, etc., are formed as we see them. The
same efforts made in swimming--_i.e._, in pushing back the water, in
order to advance and to move in this liquid--have likewise extended
the membrane situated between the digits of the frogs, the
sea-turtles, the otter, beaver, etc.

"On the contrary, the bird whose mode of life habituates it to perch
on trees, and which is born of individuals who have all contracted
this habit, has necessarily the digits of the feet longer and shaped
in another way than those of the aquatic animals which I have just
mentioned. Its claws, after a while, became elongated, pointed, and
curved or hook-like in order to grasp the branches on which the
animal often rests.

"Likewise we see that the shore bird, which is not inclined to swim,
and which moreover has need of approaching the edge of the water to
find there its prey, is in continual danger of sinking in the mud.
Now, this bird, wishing to act so that its body shall not fall into
the water, makes every effort to extend and elongate its legs. It
results from this that the long-continued habit that this bird and
the others of its race contract, of extending and continually
elongating their legs, is the _cause_ of the individuals of this
race being raised as if on stilts, having gradually acquired long,
naked legs, which are denuded of feathers up to the thighs and often
above them (_Système des Animaux sans Vertèbres_, p. 16).

"We also perceive that the same bird, wishing to catch fish without
wetting its body, is obliged to make continual efforts to lengthen
its neck. Now, the results of these habitual efforts in this
individual and in those of its race have enabled them, after a
time, to singularly elongate them--as, indeed, is proved by the long
neck of all shore birds.

"If any swimming birds, such as the swan and the goose, whose legs
are short, nevertheless have a very long neck, it is because these
birds in swimming on the surface of the water have the habit of
plunging their head down as far as they can, to catch aquatic larvæ
and different animalcules for food, and because they make no effort
to lengthen their legs.

"When an animal to satisfy its wants makes repeated efforts to
elongate its tongue, it will acquire a considerable length (the
ant-eater, green wood-pecker); when it is obliged to seize anything
with this same organ, then its tongue will divide and become forked.
That of the humming-birds, which seize with their tongue, and that
of the lizard and serpents, which use it to feel and examine objects
in front of them, are proofs of what I advocate.

"Wants, always occasioned by circumstances, and followed by
sustained efforts to satisfy them, are not limited in results, in
modifying--that is to say, in increasing or diminishing--the extent
and the faculties of organs; but they also come to displace these
same organs when certain of these wants become a necessity.

"The fishes which habitually swim in large bodies of water, having
need of seeing laterally, have, in fact, their eyes placed on the
sides of the head. Their bodies, more or less flattened according to
the _species_, have their sides perpendicular to the plane of the
water, and their eyes are placed in such a way that there is an eye
on each flattened side. But those fishes whose habits place them
under the necessity of constantly approaching the shores, and
especially the shelving banks or where the slope is slight, have
been forced to swim on their flattened faces, so as to be able to
approach nearer the edge of the water. In this situation, receiving
more light from above than from beneath, and having a special need
of being always attentive to what is going on above them, this need
has forced one of their eyes to undergo a kind of displacement, and
to assume the very singular situation which is familiar to us in the
_soles_, _turbots_, _dabs_, etc. (_Pleuronectes_ and _Achirus_). The
situation of these eyes is asymmetrical, because this results from
an incomplete change. Now, this change is entirely completed in the
rays, where the transverse flattening of the body is entirely
horizontal, as also the head. Also the eyes of the rays, both
situated on the upper side, have become symmetrical.

"The serpents which glide along the surface of the ground are
obliged chiefly to see elevated objects, or what are above their
eyes. This necessity has brought an influence to bear on the
situation of the organs of vision in these animals; and, in fact,
they have the eyes placed in the lateral and upper parts of the
head, so as to easily perceive what is above or at their sides; but
they only see for a short distance what is in front of them.
Moreover, forced to supply the lack of ability to see and recognize
what is in front of their head, and which might injure them, they
need only to feel such objects with the aid of their tongue, which
they are obliged to dart out with all their power. This habit has
not only contributed to render the tongue slender, very long and
retractile, but has also led in a great number of species to its
division, so as to enable them to feel several objects at once; it
has likewise allowed them to form an opening at the end of their
head, to enable the tongue to dart out without their being obliged
to open their jaws.

"Nothing is more remarkable than the result of habits in the
herbivorous mammals.

"The quadruped to whom circumstances and the wants which they have
created have given for a long period, as also to others of its race,
the habit of browsing on grass, only walks on the ground, and is
obliged to rest there on its four feet the greater part of its life,
moving about very little, or only to a moderate extent. The
considerable time which this sort of creature is obliged to spend
each day to fill itself with the only kind of food which it
requires, leads it to move about very little, so that it uses its
legs only to stand on the ground, to walk, or run, and they never
serve to seize hold of or to climb trees.

"From this habit of daily consuming great amounts of food which
distend the organs which receive it, and of only moving about to a
limited extent, it has resulted that the bodies of these animals are
thick, clumsy, and massive, and have acquired a very great volume,
as we see in elephants, rhinoceroses, oxen, buffaloes, horses, etc.

"The habit of standing upright on their four feet during the greater
part of the day to browse has given origin to a thick hoof which
envelops the extremity of the digits of their feet; and as their
toes are not trained to make any movement, and because they have
served no other use than as supports, as also the rest of the leg,
the most of them are short, are reduced in size, and even have ended
by totally disappearing. Thus in the _pachyderms_, some have five
toes enveloped in horn, and consequently their foot is divided into
five parts; others have only four, and still others only three. But
in the _ruminants_, which seem to be the most ancient of mammals,
which are limited only to standing on the ground, there are only two
digits on each foot, and only a single one is to be found in the
_solipedes_ (the horse, the ass).

"Moreover, among these herbivorous animals, and especially among the
ruminants, it has been found that from the circumstances of the
desert countries they inhabit they are incessantly exposed to be
the prey of carnivorous animals, and find safety only in precipitous
flight. Necessity has forced them to run swiftly; and from the habit
they have thus acquired their body has become slenderer and their
limbs much more delicate: we see examples in the antelopes, the
gazelles, etc.

"Other dangers in our climate to which are continually exposed the
deer, the roebuck, the fallow-deer, of perishing from the chase made
by man, have reduced them to the same necessity, restrained them to
similar habits, and have given rise to the same results.

"The ruminating animals only using their legs as supports, and not
having strong jaws, which are only exercised in cutting and browsing
on grass, can only fight by striking with the head, by directing
against each other the _vertex_ of this part.

"In their moments of anger, which are frequent, especially among the
males, their internal feelings, by their efforts, more strongly urge
the fluids toward this part of their head, and it there secretes the
corneous matter in some, and osseous matter mixed with corneous
matter in others, which gives origin to solid protuberances; hence
the origin of horns and antlers, with which most of these animals
have the head armed.