Jean Baptiste de Monet, Chevalier de Lamarck, was born in Picardy,
France, Aug. I, 1744, the cadet of an ancient but impoverished
house. It was his father's desire that he should enter the Church,
but his inclination was for a military life; and having, at the age
of seventeen, joined the French army under De Broglie, he had
within twenty-four hours the good fortune so to distinguish himself
as to win his commission. When the Museum of Natural History was
brought into existence in 1794 he was sufficiently well-known as a
naturalist to be entrusted with the care of the collections of
invertebrates, comprising insects, molluscs, polyps, and worms.
Here he continued to lecture until his death in 1829. Haeckel,
classifying him in the front rank with Goethe and Darwin,
attributes to him "the imperishable glory of having been the first
to raise the theory of descent to the rank of an independent
scientific theory." The form of his theory was announced in 1801,
but was not given in detail to the world until 1809, by the
publication of his "Zoological Philosophy" ("Philosophie
Zoologique"). The Lamarckian theory of the hereditary transmission
of characters acquired by use, disuse, etc., has still a following,
though it is controverted by the schools of Darwin and Weissmann.
Lamarck died on December 18, 1829.
_I.--The Ladder of Life_
If we look backwards down the ladder of animal forms we find a
progressive degradation in the organisation of the creatures comprised;
the organisation of their bodies becomes simpler, the number of their
faculties less. This well-recognised fact throws a light upon the order
in which nature has produced the animals; but it leaves unexplained the
fact that this gradation, though sustained, is irregular. The reason
will become clear if we consider the effects produced by the infinite
diversity of conditions in different parts of the globe upon the
general form, the limbs, and the very organisation of the animals in
question.
It will, in fact, be evident that the state in which we find all animals
is the product, on the one hand, of the growing composition of the
organisation which tends to form a regular gradation; and that, for the
rest, it results from a multitude of circumstances which tend
continually to destroy the regularity of the gradation in the
increasingly composite nature of the organism.
Not that circumstances can effect any modification directly. But changed
circumstances produce changed wants, changed wants changed actions. If
the new wants become constant the animals acquire new habits, which are
no less constant than the wants which gave rise to them. And such new
habits will necessitate the use of one member rather than another, or
even the cessation of the use of a member which has lost its utility.
We will look at some familiar examples of either case. Among vegetables,
which have no actions, and therefore no habits properly so called, great
differences in the development of the parts do none the less arise as a
consequence of changed circumstances; and these differences cause the
development of certain of them, while they attenuate others and cause
them to disappear. But all this is caused by changes in the nutrition of
the plant, in its absorptions and transpirations, in the quantity of
heat and light, of air and moisture, which it habitually receives; and,
lastly, by the superiority which certain of its vital movements may
assert over the others. There may arise between individuals of the same
species, of which some are placed in favourable, others amid
unfavourable, conditions, a difference which by degrees becomes very
notable.
Suppose that circumstances keep certain individuals in an ill-nourished
or languid state. Their internal organisation will at length be
modified, and these individuals will engender offspring which will
perpetuate the modifications thus acquired, and thus will in the end
give place to a race quite distinct from that of which the individual
members come together always under circumstances favourable to their
development.
For instance, if a seed of some meadow flower is carried to dry and
stony ground, where it is exposed to the winds and there germinates, the
consequence will be that the plant and its immediate offspring, being
always ill-nourished, will give rise to a race really different from
that which lives in the field; yet this, none the less, will be its
progenitor. The individuals of this race will be dwarfed; and their
organs, some being increased at the expense of the rest, will show
distinctive proportions. What nature does in a long time we do every day
ourselves. Every botanist knows that the vegetables transplanted to our
gardens out of their native soil undergo such changes as render them at
last unrecognisable.
Consider, again, the varieties among our domestic fowls and pigeons, all
of them brought into existence by being raised in diverse circumstances
and different countries, and such as might be sought in vain in a state
of nature. It is matter of common knowledge that if we raise a bird in a
cage, and keep it there for five or six years, it will be unable to fly
if restored to liberty. There has, indeed, been no change as yet in the
form of its members; but if for a long series of generations individuals
of the same race had been kept caged for a considerable time, there is
no room for doubt that the very form of their limbs would little by
little have undergone notable alteration. Much more would this be the
case if their captivity had been accompanied by a marked change of
climate, and if these individuals had by degrees accustomed themselves
to other sorts of food and to other measures for acquiring it. Such
circumstances, taken constantly together, would have formed insensibly a
new and clearly denned race.
The following example shows, in regard to plants, how the change of
some important circumstance may tend to change the various parts of
these living bodies.
So long as the _ranunculus aquatilis_, the water buttercup, is under
water its leaves are all finely indented, and the divisions are
furnished with capillaries; but as soon as the stalk of the plant
reaches the surface the leaves, which develop in the air, are broadened
out, rounded, and simply lobed. If the plant manages to spring up in a
soil that is merely moist, and not covered with water, the stems will be
short, and none of the leaves will show these indentations and
capillaries. You have then the _ranunculus hederaceus_, which botanists
regard as a distinct species.
Among animals changes take place more slowly, and it is therefore more
difficult to determine their cause. The strongest influence, no doubt,
is that of environment. Places far apart are different, and--which is
too commonly ignored--a given place changes its climate and quality with
time, though so slowly in respect of human life that we attribute to it
perfect stability. Hence it arises that we have not only extreme
changes, but also shadowy ones between the extremes.
Everywhere the order of things changes so gradually that man cannot
observe the change directly, and the animal tribes in every place
preserve their habits for a long time; whence arises the apparent
constancy of what we call species--a constancy which has given birth in
us to the idea that these races are as old as nature.
But the surface of the habitable globe varies in nature, situation, and
climate, in every variety of degrees. The naturalist will perceive that
just in proportion as the environment is notably changed will the
species change their characters.
It must always be recognised:
(1) That every considerable and constant change in the environment of a
race of animals works a real change in their wants.
(2) That every change in their wants necessitates new actions to supply
them, and consequently new habits.
(3) That every new want calling for new actions for its satisfaction
affects the animal in one of two ways. Either it has to make more
frequent use of some particular member, and this will develop the part
and cause it to increase in size; or it must employ new members which
will grow in the animal insensibly in response to the inward yearning to
satisfy these wants. And this I will presently prove from known facts.
How the new wants have been able to attain satisfaction, and how the new
habits have been acquired, it will be easy to see if regard be had to
the two following laws, which observation has always confirmed.
FIRST LAW.--In every animal which has not arrived at the term of
its developments, the more frequent and sustained use of any organ
strengthens, develops, and enlarges that organ, and gives it a
power commensurate with the duration of this employment of it. On
the other hand, constant disuse of such organ weakens it by
degrees, causes it to deteriorate, and progressively diminishes its
faculties, so that in the end it disappears.
SECOND LAW.--All qualities naturally acquired by individuals as the
result of circumstances to which their race is exposed for a
considerable time, or as a consequence of a predominant employment
or the disuse of a certain organ, nature preserves to individual
offspring; provided that the acquired modifications are common to
the two sexes, or, at least, to both parents of the individual
offspring.
Naturalists have observed that the members of animals are adapted to
their use, and thence have concluded hitherto that the formation of the
members has led to their appropriate employment. Now, this is an error.
For observation plainly shows that, on the contrary, the development of
the members has been caused by their need and use; that these have
caused them to come into existence where they were wanting.
But let us examine the facts which bear upon the effects of employment
or disuse of organs resulting from the habits which a race has been
compelled to form.
_II.--The Penalties of Disuse_
Permanent disuse of an organ as a consequence of acquired habits
gradually impoverishes it, and in the end causes it to disappear, or
even annihilates it altogether.
Thus vertebrates, which, in spite of innumerable particular
distinctions, are alike in the plan of their organisation, are generally
armed with teeth. Yet those of them which by circumstances have acquired
the habit of swallowing their prey without mastication have been liable
to leave their teeth undeveloped. Consequently, the teeth have either
remained hidden between the bony plates of the jaws, or have even been,
in the course of time, annihilated.
The whale was supposed to have no teeth at all till M. Geoffrey found
them hidden in the jaws of the foetus. He has also found in birds the
groove in which teeth might be placed, but without any trace of the
teeth themselves. A similar case to that of the whale is the ant-eater
(_nyomecophaga_), which has long given up the practice of mastication.
Eyes in the head are an essential part of the organisation of
vertebrates. Yet the mole, which habitually makes no use of the sense of
sight, has eyes so small that they can hardly be seen; and the aspalax,
whose habits-resemble a mole's, has totally lost its sight, and shows
but vestiges of eyes. So also the proteus, which inhabits dark caves
under water.
In such cases, since the animals in question belong to a type of which
eyes are an essential part, it is clear that the impoverishment, and
even the total disappearance, of these organs are the results of long
continued disuse.
With hearing, the case is otherwise. Sound traverses everything.
Therefore, wherever an animal dwells it may exercise this faculty. And
so no vertebrate lacks it, and we never find it re-appearing in any of
the lower ranges. Sight disappears, re-appears, and disappears again,
according as circumstances deny or permit its exercise.
Four legs attached to its skeleton are part of the reptile type; and
serpents, particularly as between them and the fishes come the
batrachians--frogs, etc.--ought to have four legs.
But serpents, having acquired the habit of gliding along the ground, and
concealing themselves amid the grass, their bodies, as a consequence of
constantly repeated efforts to lengthen themselves out in order to pass
through narrow passages, have acquired considerable length of body which
is out of all proportion to their breadth.
Now, feet would have been useless to these animals, and consequently
would have remained unemployed; for long legs would have interfered with
their desire to go on their bellies; and short legs, being limited in
number to four, would have been incapable of moving their bodies. Thus
total disuse among these races of animals has caused the parts which
have fallen into disuse totally to disappear.
Many insects, which by their order and genus should have wings, lack
them more or less completely for similar reasons.
_III.--The Advantages of Use_
The frequent use of an organ, if constant and habitual, increases its
powers, develops it, and makes it acquire dimensions and potency such
as are not found among animals which use it less.
Of this principle, the web-feet of some birds, the long legs and neck of
the stork, are examples. Similarly, the elongated tongue of the
ant-eater, and those of lizards and serpents.
Such wants, and the sustained efforts to satisfy them, have also
resulted in the displacement of organs. Fishes which swim habitually in
great masses of water, since they need to see right and left of them,
have the eyes one upon either side of the head. Their bodies, more or
less flat, according to species, have their edges perpendicular to the
plane of the water; and their eyes are so placed as to be one on either
side of the flattened body. But those whose habits bring them constantly
to the banks, especially sloping banks, have been obliged to lie over
upon the flattened surface in order to approach more nearly. In this
position, in which more light falls on the upper than on the under
surface, and their attention is more particularly fixed upon what is
going on above than on what is going on below them, this want has forced
one of the eyes to undergo a kind of displacement, and to keep the
strange position which it occupies in the head of a sole or a turbot.
The situation is not symmetrical because the mutation is not complete.
In the case of the skate, however, it is complete; for in these fish the
transverse flattening of the body is quite horizontal, no less than that
of the head. And so the eyes of a skate are not only placed both of them
on the upper surface, but have become symmetrical.
Serpents need principally to see things above them, and, in response to
this need, the eyes are placed so high up at the sides of the head that
they can see easily what is above them on either side, while they can
see in front of them but a very little distance. To compensate for this,
the tongue, with which they test bodies in their line of march, has been
rendered by this habit thin, long, and very contractile, and even, in
most species, has been split so as to be able to test more than one
object at a time. The same custom has resulted similarly in the
formation of an opening at the end of the muzzle by which the tongue may
be protruded without any necessity for the opening of the jaws.
The effect of use is curiously illustrated in the form and figure of the
giraffe. This animal, the largest of mammals, is found in the interior
of Africa, where the ground is scorched and destitute of grass, and has
to browse on the foliage of trees. From the continual stretching thus
necessitated over a great space of time in all the individuals of the
race, it has resulted that the fore legs have become longer than the
hind legs, and that the neck has become so elongated that the giraffe,
without standing on its hind legs, can raise its head to a height of
nearly twenty feet. Observation of all animals will furnish similar
examples.
None, perhaps, is more striking than that of the kangaroo. This animal,
which carries its young in an abdominal pouch, has acquired the habit of
carrying itself upright upon its hind legs and tail, and of moving from
place to place in a series of leaps, during which, in order not to hurt
its little ones, it preserves its upright posture. Observe the result.
(1) Its front limbs, which it uses very little, resting on them only in
the instant during which it quits its erect posture, have never acquired
a development in proportion to the other parts; they have remained thin,
little, and weak.
(2) The hind legs, almost continually in action, whether to bear the
weight of the whole body or to execute its leaps, have, on the contrary,
obtained a considerable development; they are very big and very strong.
(3) Finally, the tail, which we observe to be actively employed, both to
support the animal's weight and to execute its principal movements, has
acquired at its base a thickness and a strength that are extremely
remarkable.
When the will determines an animal to a certain action, the organs
concerned are forthwith stimulated by a flow of subtle fluids, which are
the determining cause of organic changes and developments. And
multiplied repetitions of such acts strengthen, extend, and even call
into being the organs necessary to them. Now, every change in an organ
which has been acquired by habitual use sufficient to originate it is
reproduced in the offspring if it is common to both the individuals
which have come together for the reproduction of their species. In the
end, this change is propagated and passes to all the individuals which
come after and are submitted to the same conditions, without its being
necessary that they should acquire it in the original manner.
For the rest, in the union of disparate couples, the disparity is
necessarily opposed to the constant propagation of such qualities and
outward forms. This is why man, who is exposed to such diversity of
conditions, does not preserve and propagate the qualities or the
accidental defects which he has been in the way of acquiring. Such
peculiarities will be produced only in case two individuals who share
them unite; these will produce offspring bearing similar
characteristics, and, if successive generations restrict themselves to
similar unions, a distinct race will then be formed. But perpetual
intermixture will cause all characters acquired through particular
circumstances to disappear. If it were not for the distances which
separate the races of men, such intermixture would quickly obliterate
all national distinctions.
_IV.--The Conclusion_
Here, then, is the conclusion to which we have come. It is a fact that
every genus and species of animal has its characteristic habits combined
with an organisation perfectly in harmony with them. From the
consideration of this fact one of two conclusions must follow, and that
though neither of them can be proved.
(1) The conclusion admitted hitherto--that nature (or its Author) in
creating the animals has foreseen all the possible sets of circumstances
in which they would have to live, has given to each species a constant
organisation, and has shaped its parts in a determined and invariable
way so that every species is compelled to live in the districts and the
climates where it is actually formed, and to keep the habits by which it
is actually known.
(2) My own conclusion--that nature has produced in succession all the
animal species, beginning with the more imperfect, or the simpler, and
ending with the more perfect; that in so doing it has gradually
complicated their organisation; and that of these animals, dispersed
over the habitable globe, every species has acquired, under the
influence of the circumstances amid which it is found, the habits and
modifications of form which we associate with it.
To prove that the second of these hypotheses is unfounded, it will be
necessary, first, to prove that the surface of the globe never varies in
character, in exposure, situation, whether elevated or sheltered,
climate, etc.; and, secondly, to prove that no part of the animal world
undergoes, even in the course of long periods of time, any modification
through change of circumstances, or as a consequence of a changed manner
of life and action.
Now, a single fact which establishes that an animal, after a long period
of domestication, differs from the wild stock from which it derives, and
that among the various domesticated members of a species may be found
differences no less marked between individuals which, have been
subjected to one use and those which have been subjected to another,
makes it certain that the former conclusion is not consistent with the
laws of nature, and that the second is.
Everything, therefore, concurs to prove my assertion, to wit--that it is
not form, whether of the body or of the parts, which gives rise to the
habits of animals and their manner of life; but that, on the contrary,
in the habits, the manner of living, and all the other circumstances of
environment, we have those things which in the course of time have built
up animal bodies with all their members. With new forms new faculties
have been acquired, and little by little nature has come to shape
animals and all living things in their present forms.