Zoological Philosophy
by
J. B. Lamarck
[This translation, which has been prepared by Ian
Johnston of Malaspina University-College,
Nanaimo, BC, Canada, (now Vancouver Island University) is in the public domain,
and may be used by anyone, in whole or in part, without permission and without
charge, provided the source is acknowledged, released September 1999]
First Part
Considerations of the Natural
History of Animals, Their Characteristics, Their Interrelationships, Their
Organic Structure, Their Distribution, Their Classification and Their Species
Chapter Three
Concerning Speciation Among Living Things and the Idea Which We Should Attach to
This Word
It is
not a futile pursuit firmly to establish the idea which we should form about
what are called species among living creatures and to investigate whether it is
true that species have an absolute constancy, are as old as nature, and have
all existed originally just as we see them today, or whether, subject to
changes which could have taken place in the circumstances relevant to them,
they have not changed their characteristics and shape with the passage of time
(although extremely slowly).
The
illumination of this question is not only of interest to our zoological and
botanical knowledge but also is essential to the history of the earth.
I will
show in one of the chapters which follow that each species has received from
the influence of the circumstances which it encounters over a long period the
habits which we know about and that these habits have themselves exerted
influences on the parts of each individual of the species, to the point where
they have modified these parts and have made them appropriate to the acquired habits.
Let us first examine the idea which has developed about what is called a
species.
We
call species every collection of similar individuals produced by other
individuals just like themselves.
This
definition is exact, for every individual enjoying life always resembles very
closely the one or those from which it came. But we add to this definition the
assumption that the individuals who make up a species never vary in their
specific characteristics and that therefore the species has an absolute constancy
in nature.
It is
precisely this assumption that I propose to contest, because clear proofs
obtained through observation establish that it is not well founded.
The
assumption almost universally admitted that living things make up eternally
distinct species on account of their invariable characteristics and that the
existence of these species is as ancient as nature herself was established at a
time when people had not observed nature sufficiently and when the natural
sciences were still almost nothing. The assumption is contradicted every day in
the eyes of those who have looked at a great deal and have followed nature for
a long time, and who have reaped the benefits of the large and rich collections
in our museum.
Moreover,
all those who are very busy studying natural history know that nowadays
naturalists are extremely embarrassed in their attempts to define the objects
which they have to consider species. In fact, not knowing that species have a
constancy only relative to the duration of the circumstances in which all the
individuals composing them are found and that some of these individuals, having
undergone variations, make up races which modulate into some other
neighbouring species, naturalists make decisions arbitrarily, by describing
some individuals observed in different countries and in various environments as
varieties and others as species. As a result, that section of work concerning
the determination of species is becoming day by day increasingly defective,
that is, more embarrassing and confusing.
In
truth, it has been observed for a long time that there exist collections of
individuals who so resemble each other in their organic structure, as well as
by the totality of their parts, and who remain in the same condition generation
after generation for as long as we have known about them that people have
believed themselves justified in regarding these collections of similar
individuals as making up just as many invariable species.
Now,
not having attended to the fact that the individuals of a species must
perpetuate themselves without variation, as long as the circumstances which
influence their manner of life do not essentially vary and the existing
prejudices agreeing well enough with the successive regeneration of similar
individuals, people have assumed that each species did not vary, was also as
old as nature, and was uniquely created by the work of the Supreme Author of
everything which exists.
There
is no doubt that nothing exists except by the will of the sublime Author of
everything. But can we assign some rules to Him in the execution of His will
and establish the method which He followed in this matter? Could not His
infinite power have been capable of creating an order of things which gave life
successively to everything which we see, as well as to everything existing
which we do not know about?
To be
sure, whatever His will, the immensity of his power is still the same and
whatever the manner in which the Supreme Will carried out His work, nothing can
diminish His grandeur.
Therefore,
respecting the decrees of this infinite wisdom, I confine myself within the
limits of a simple observer of nature. Then, if I manage to unravel something
of the progress which nature has followed to bring about its productions, I
will say, without fear of being wrong, that it has pleased her Author that
nature has had this faculty and this power.
The
notion of species among living creatures which people formed was very simple,
easy to grasp, and seemed confirmed by the constancy in the apparent form of
individuals which reproduction or generation perpetuated. Such individuals
create for us a great number of those alleged species which we see every day.
However,
the more we advance our knowledge of the different organic bodies which cover
the surface of the earth almost everywhere, the greater becomes our
embarrassment about determining what ought to be regarded as a species and, for
even more compelling reasons, about limiting and distinguishing genera.
The
more we collect the productions of nature and our collections grow richer, the
more we see almost all the gaps being filled and our lines of separation being
erased. We find ourselves reduced to an arbitrary determination, which
sometimes leads us to seize upon the least differences among the varieties to
form the characteristic of what we call species. Sometimes this makes us call
certain individuals with slight differences a variety of some species. Other
people consider these individuals constitute a separate species.
Let me
repeat myself: the more our collections increase, the more we encounter proofs
that everything is more or less nuanced, the remarkable differences disappear,
and as often as not nature makes available to us for the creation of
distinctions only minute and, so to speak, puerile particularities.
How
many genera, among animals and plants, are so extensive in the quantity of
species which people assign to them, that the study and the definition of these
species are now almost unworkable! The species in these genera, arranged in a
series and set beside each other according to an analysis of their natural
affinities, display, along with those which are close to them, differences so
slight that they are modifications of each other and these species get
confused, in some way, amongst each other, leaving almost no way of determining
in some explicit way the small differences which distinguish them.
Those
who have concerned themselves long and diligently with the determination of
species and who have looked at rich collections are the only ones who can know
at what point, among living things, species merge into each other and who could
convince themselves that, in those places where we see isolated species, the
phenomenon occurs only because we are missing other closely related species
which we have not yet collected.
For
all the above remarks, I do not wish to state that existing animals form a very
simple series, equally modified throughout. But I do say that they form a branching
series, with irregular gradations, something which has no discontinuity in its
parts or which, at least, has not always had them, if it is true that as a
result of some lost species such discontinuity occurs here and there. From this
it follows that species which end each branch of this general series have, at
least on one side, other closely related species which meld into them. This
well known state of things leads me now to provide an illustration.
I do
not require any hypothesis nor any assumption for such
a demonstration. I call all observing naturalists to vouch for its truth.
Not
only many genera but some entire orders and sometimes even the classes already
offer us almost complete sections of the state of things which I am going to
point to.
Now,
when, in this example, one arranges the species in a series, placing them
correctly following their natural affinities, if you choose one and then,
making a jump over several others, take another species a little distant, these
two species, when compared, will present to you major differences between them.
This was the manner in which we started to see nature’s productions which we
find most frequently within reach. Then the generic and specific distinctions
were very easy to establish. But now that our collections are extremely
profuse, if you follow the series which I have cited immediately above from the
species you first chose right up to the one which you selected second (which is
very different from the first), you will reach that second species through a
series of slight modifications without having noticed distinctions worthy of
attention.
Here
is the question: What experimental zoologist or botanist has not explored the
basis of what I have just revealed?
How
then are we to study species or how are we able to determine them with a
reliable method, among this multitude of polyps of all the orders, radiates,
worms, and, above all, insects, where the individual order butterfly, Phalaena, Noctua, Tinea, flies, Ichneumon, Curculio, Cerambix,
chafers, rose-chafers, and so on and so on already display so many closely
related species, modifying into and almost overlapping each other?
What a
crowd of shell creatures the mollusks show us from all countries and all seas,
eluding our ways of distinguishing them and wearing out our resources on this
question.
Go
back up to the fish, reptiles, birds, even to mammals. You will see everywhere,
apart from the gaps which still have to be filled, the modifications which link
up neighbouring species, even genera, leaving hardly any places for our
ingenuity to establish good distinctions.
And in
its various parts does not botany, which focuses on the other series making up
the plants, display exactly the same state of things?
In
fact, what difficulties are not experienced nowadays in studying and
determining species in the genera Lichen, Fucus, Carex, Poa, Piper, Euphorbia,
Erica, Hieracium, Solanum,
Geranium, Mimosa, and on and on?
When
we formed these genera, we knew only a small number of their species; thus,
they were easy to distinguish. But now that almost all the gaps between them
have been filled, our specific differences are necessarily minute and very
frequently insufficient.
Having
well established this state of affairs, let us examine the causes which can
have given rise to it. Let us see if nature possess
means for that and if observation could have given us insight into this
question.
A
number of facts teach us that, to the extent that the individuals of one of our
species change their situation, climate, manner of life, or habits, they obtain
from that change influences which little by little alter the constancy and the
proportions of their parts, shape, faculties, even their organic structure,
with the result that everything in them participates, over time, in the
mutations which they have experienced.
In the
same climate, significantly different situations and exposures at first simply
induce changes in the individuals who find themselves confronted with them. But
as time passes, the continual difference in the situation of the individuals I’m
talking about, who live and reproduce successively in the same circumstances,
leads to changes in them which become, in some way, essential to their being,
so that after many generations, following one after the other, these
individuals, belonging originally to another species, find themselves at last
transformed into a new species, distinct from the other.
For
example, if the seeds of a grass or of any other plant common to a humid
prairie are transported, by some circumstance or other, at first to the slope
of a neighbouring hill, where the soil, although at a higher altitude, is still
sufficiently damp to allow the plant to continue living, if then, after living
there and reproducing many times in that spot, the plant little by little
reaches the almost arid soil of the mountain slope and succeeds in
subsisting there and perpetuates itself through a sequence of generations, it
will then be so changed that botanists who come across it there will create a special
species for it.
The
same thing happens to animals which circumstances have forced to change their
climate, manner of life, and habits. But for these, the causal influences which
I have just mentioned require even more time than is the case with plants in
order to effect notable changes in the individuals.
The
idea of including, in the name species, a collection of similar individuals who
perpetuate creatures like themselves through reproduction and who have thus
existed in the same form for as long as nature necessarily requires that the
individuals of the same species, in their reproductive acts, cannot mate with
the individuals of another species.
Unfortunately,
observation has demonstrated and still establishes every day that this idea has
no foundation whatsoever. For hybrids, very well known among
plants, and the matings which we often see between
individuals of very different species among animals attest to the fact that the
limits between these species, supposedly constant, were not as firm as people
have imagined.
To be
sure, often nothing results from these odd matings,
above all when they involve very different types, and then the individuals
produced are, in general, infertile. But then again, when the disparity is less
great, we know that the flaws in question do not occur. Now, this method by
itself is sufficient to create varieties gradually which then become races, and
which, in time, make up what we call species.
In
order to evaluate whether the traditional idea of species has some real
foundation, let us look again at points which I have already established. They
enable us to see the following:
(1)
All organic bodies of our earth are true products of nature, which she has
brought forth successively over a long period of time;
(2) In
her progress, nature began, and begins again every day, by creating the
simplest organic bodies, and she does not directly create anything except by
this process, that is to say, by these first beginnings of organic structure
which are designated by the expression spontaneous generation.
(3)
The first beginnings of animals and plants were formed in appropriate places
and circumstances. Once the faculties of a commencing life and of organic
movement were established, these animals and plants of necessity gradually
developed organs, and, in time, they diversified these organs, as well as their
parts.
(4)
The faculty of growth in each portion of an organic body is inherent in the
first effects of life; it gave rise to different ways of multiplication and reproduction
of individuals. In this process, the progress acquired in the composition of
the organic structure and in the shape and diversity of parts was maintained.
(5)
With the help of a sufficient lapse of time, of circumstances which were
necessarily favourable, of changes which every point on the surface of the
earth has successively undergone, in a word, with the assistance of the power
which new situations and habits have for modifying the organs of a body endowed
with life, all those which exist now have been imperceptibly shaped just as we
see them.
(6)
Finally, after a sequence of events like the above, living bodies have each
experienced greater or lesser changes in the condition of their organic
structure and their parts. What we call species have
been created in this way imperceptibly and successively among them; they have a
constancy which is only relative to their condition and cannot be as old as
nature.
But,
someone will say, when people want to assume that with the help of a great deal
of time and an infinite variation in circumstances, nature has gradually formed
the various animals which we know about, would they not have this assumption
challenged by the single consideration of the admirable diversity which we see
in the instincts of these different animals and by the consideration of the
marvels in every genus which their various sorts of work offer?
Dare
one carry the systematic spirit so far as to say that it is nature alone which
has created this astonishing diversity of means, tricks, dexterity, precaution,
and patience, so often illustrated to us by the industry of animals? Is not
what we observe in this respect in the class of insects alone a thousand times
more than sufficient to make us feel that limiting the power of nature would
not permit her to produce on her own so many marvels and to impress on us the
most persistent belief that here the will of the supreme Author of everything
was necessary and alone sufficed to bring into existence so many admirable
things?
Without
doubt, one would have to be foolhardy or rather entirely idiotic to claim to
assign limits to the power of the first Author of everything. But, by that
alone, no one can dare to say that this infinite power could not have willed
what nature herself shows us it has willed.
This
being the case, if I discover that nature herself brings about all these
wonders which have just been mentioned, that she has created organic
structures, life, even feeling, that she has multiplied and diversified within
limits which we do not know, the organs and faculties of organic bodies in whom
she supports and propagates existence, that she has created in animals, by the
sole route of needs, which establish and direct habits, the source of all
actions, all faculties, from the simplest right up to those which make up
instinct, work, and finally reasoning, must I not recognize in this power of
nature, that is to say, in the order of existing things, the work of the will
of her divine Author, who has been able to will that she has this ability?
Will I
admire less the grandeur of the power of this first cause of everything if it
has pleased Him that things were like this, that if, by so many acts of His
will, this power was occupied and still is continually occupied with the
details of all the particular things of creation, all the variations, all the
developments and improvements, all the destruction and all the renewals, in a
word, of all the transformations which universally happen in existing things?
Now, I
hope to prove that nature possesses the means and the abilities necessary for
her to produce by herself what we admire in her.
However,
another objection is that everything which we see announces, concerning the
condition of living things, an unalterable constancy in the conservation of
form. And it is believed that all the animals whose history has been handed
down to us in the past two or three thousand years have always been the same
and have lost nothing and acquired nothing in the improvement of their organs
and in the shape of their parts.
Moreover,
in order to give this apparent stability over a long period the status of a
verified fact, an attempt has just been made to provide particular written
proofs for it in the Report On the Collections of
Natural History Brought Back from Egypt by M. Geoffroy.
Those writing the report express themselves on this point in the following way:
“First, the collection has this remarkable quality, that we can say it contains animals of all centuries. For a long time now, people have wanted to know if species change their form with the passage of time. This apparently futile question is essential to the earth’s history and, consequently, to the solution of a thousand other questions, which are not irrelevant to the most serious purposes of human reverence.
We have never been in a better position to make a decision about a large number of remarkable species and for several thousands of others. It appears that the superstition of the ancient Egyptians was inspired by nature, with a view to leaving a monument of her history. . . .
“It is not possible, the writers of the report continue, to control one’s imaginative excitement when one sees still preserved with the smallest bones, the smallest hairs, and perfectly recognizable, such an animal which had, two or three thousand years ago, priests or altars in Thebes or Memphis. But without losing ourselves in all the ideas which this link generates, let us limit ourselves to revealing to you that, as a result of this part of Geoffroy’s collection, these animals are perfectly similar to today’s.” Annales du Muséum d’Hist. natur., vol. I, p. 235, and 236.
I do
not deny the conformity in the appearance of these animals with individuals of
the same species alive today. Thus, the birds which the Egyptians adored and
embalmed, two or three thousand years ago, are still totally similar to those
which live at present in that country.
It
would surely be really odd if the case was otherwise. For the situation of
Egypt and its climate are still to a very large degree what they were at that
period. Now, the birds which live there at present are still in the same
circumstances where they were then and could not have been forced to change
their habits.
Moreover,
who does not sense that birds, which can so easily move on and choose places
agreeable to them, are less subject to variation in local circumstances than
many other animals and thus less challenged in their habits.
In
fact, there is nothing in the observation mentioned above which contradicts the
ideas I have revealed in this matter and, above all, which proves that the
animals under discussion have existed for all time in nature. It proves only
that they were present in Egypt two or three thousand years ago. And anyone in
the habit of thinking about things, while at the same time observing what
nature shows us of the monuments to its own antiquity, easily appreciates the
value of a duration of two or three thousand years in comparison with that
antiquity.
In
addition, we can be sure that this apparent stability of things in nature will
always be taken by common opinion as the truth of things, because, in general,
people do not judge anything except in relation to themselves.
For
the man who, in this matter, judges only according to changes which he
perceives himself, the intervals between these mutations are conditions of
stability which appear unlimited to him, because of the brevity of the lifetime
of the individuals in his species. Moreover, since the records of his
observations and the factual notes which he has been able to enter into his
accounts go back only a few thousand years, a length of time infinitely great
compared with him, but extremely small compared to durations which have
witnessed the occurrence of the great changes the surface of the earth has
undergone, everything appears stable on the planet which he inhabits, and he is
encouraged to dismiss the signs presented to him everywhere by the monuments
piled up around him or buried in the soil under his feet as he walks.
Quantities
of space and time are relative. If man really wishes to imagine this truth,
then he will be reserved in his judgments about the stability which he
attributes in nature to the state of things which he observes. See in my Recherches sur les
corps vivans, l’appendice,
p. 141.
In
acknowledging the imperceptible changes in species and the modification which
individuals undergo, to the extent that they are forced to vary their habits or
to acquire new ones, we are not confined solely to a consideration of the very
small extents of time which our observations can include to allow us to see
these changes. For, in addition to this induction, a number of facts collected
for many years now also illuminate the question which I am examining, in such a
way that it does not remain uncertain. And I can say that nowadays our
observational knowledge is too advanced for the answer we are looking for not
to be obvious.
In
addition the fact that we know about the influences and the results of
heterogeneous reproduction, we certainly know nowadays that a forceful and
sustained change in the environment and in the habits and ways of life of animals works to bring about, after a suitable length of
time, a very remarkable change in the individuals exposed to it.
The
animal which lives freely in the plains where it habitually runs quickly and
the bird which meets its needs as it continually crosses huge expanses in the
air, when caged up, one in the compartments of a menagerie or in our stables,
the other in our cages or in our poultry yards, there undergo over time
significant influences, especially after a sequence of reproductive cycles in a
condition which makes them acquire new habits.
In
that new location, the first loses a large part of its lightness and agility.
Its body becomes more dense; its limbs lose power and
suppleness, and its faculties are no longer the same. The second becomes heavy,
hardly knows how to fly any more, and acquires more flesh in all its parts.
In the
sixth chapter of this first part, I will have occasion to prove by well known
facts the power of changes in circumstances to give animals new needs and to
lead to new actions, the power of repeated new actions to bring about new
habits and new tendencies, and finally, the power of the more or less frequent
use of this or that organ to modify that organ, whether by making it stronger,
developing and enlarging it, or by making it more feeble, diminishing and
weakening it, and even making it disappear.
In the
case of plants, we will see the same thing concerning the effects of new
circumstances on their manner of living and on the condition of their parts.
The result is that we will no longer be astonished to see the considerable
changes which we have made in those plants we have cultivated for a long time.
Thus,
among living things, nature, as I have already said, offers us in an indisputable manner only individuals which succeed
each other in sequence one after the other in reproduction and which come from
each other. But species among them have only a relative constancy and are not
invariable except temporarily.
Nevertheless,
to facilitate our study and our knowledge of so many different bodies, it is
useful to give the name species to the entire collection of similar individuals
which reproduction perpetuates in the same condition, as long as their living
circumstances do not change sufficiently to vary their habits, characteristics,
and shape.
On Species Which Have Been Called
Lost
There
is still for me the issue of knowing if the means which nature adopted to
assure the conservation of species or races has been so inadequate that entire
races have now been wiped out or lost.
However,
the fossil remains which we find buried in the soil in so many different places
present us with the remains of a multitude of various animals which have
existed. Among them there are found only a very small number who, to our
knowledge, have analogous creatures like them now alive.
From that,
can we logically conclude that the species which we find in the fossil state
and for which there is no living individual exactly similar known to us does
not exist any more in nature? There are still so many
portions of the earth’s surface into which we have not gone, so many others
which people capable of making observations have not crossed except casually,
and still so many others, like the different parts of the sea bottom, where we
have few means for identifying the animals which live there, that these
different places could well conceal species unknown to us.
If
there are some species truly lost, this can only be, without any doubt, among
the large animals which live in the dry parts of the earth where man, through
the absolute dominion which he exerts, has been able to succeed in destroying
all the individuals of some species which he did not wish to preserve or to
reduce to domesticity. Hence arises the possibility that the animals of Cuvier’s
genera palaeotherium, anoplotherium,
megalonix, megatherium,
mastodon and some other species of genera already known exist no longer in
nature. However, that is only a possibility.
But
the animals which live in the watery depths, above all in ocean waters, as well
as all the small-bodied species living on the surface of the earth and
breathing air are protected against the destruction of their species at the
hand of man. Their reproductive rate is so large and the means which they have
to save themselves from his pursuits or traps are such that there is no
evidence that he can destroy the entire species of any of these animals.
Thus,
it is only the large terrestrial animals which can be exposed to destruction of
their species at the hand of man. Such an event could have taken place. But its
reality has not yet been completely proved.
However,
among the fossil remains which we find of so many animals who
have existed there is a very large number belonging to animals for whom totally
similar living analogues are unknown. And among these, most belong to the shelled
mollusks, so that only the shells remain of these animals.
Now,
if a number of these fossil shells reveal differences which do not permit us,
according to accepted opinions, to regard them as analogous to neighbouring
species which we know about, surely it must follow that these shells belong to
species truly lost? Why, moreover, would they be lost, since man could not have
brought about their destruction? On the contrary, might it not be possible that
the fossil individuals in question belong to species still existing but which
have changed over time and have given way to species presently living which we
find near by? The considerations which follow and our
observations in the course of this work will make this assumption highly
probable.
Every
informed observer knows that nothing is constantly in the same state on the
surface of the earth. In time, everything there undergoes various changes more
or less constantly. High places are continuously eroded by the alternating
actions of the sun, rain, and still other causes. Everything detached from
there is drawn away toward places lower down. The beds of streams, rivers, even
the seas vary in their shape, depth, and imperceptibly move. In a word,
everything on the surface of the earth changes its position, shape, nature, and
aspect, and even the climates of the earth’s various regions are not any more
stable.
Now,
if, as I will be attempting to reveal, variations in the circumstances of
living things, above all for animals, lead to changes in needs, habits, and
ways of life, and if these changes give rise to modification of or developments
in their organs and the shape of their parts, we must sense that imperceptibly
all living bodies whatsoever must vary, especially in their shapes or external
characteristics, although this variation will become noticeable only after a
considerable time.
Thus,
it is not astonishing if, among the numerous fossils which we find in all the
dry places of the earth and which present to us so many animals which existed
in previous times, there are found so few whose living analogues we recognize.
By
contrast, if there is anything which should astonish us it is to encounter
among these numerous fossil remains of bodies once living some still having
living analogues we do know about. This fact, which our fossil collections
confirm, should lead us to assume that the fossil remains of animals whose
living analogues we know about are the least ancient fossils. The species to
which each of them belongs has undoubtedly not yet had sufficient time to vary
in some of its forms.
Naturalists
who have not perceived the changes which most animals experience with the
passage of time, wishing to explain the facts relevant to the observed fossils,
as well as to the known revolutions in different places on the surface of the
earth, have assumed that a universal catastrophe took place with respect to the
terrestrial globe and destroyed a large number of the species then in
existence.
It is
a pity that this convenient method of dealing with one’s embarrassment when one
wants to explain the operations of nature whose causes
one been unable to grasp has no foundation except in the imagination which
created it. It cannot be supported with a single proof.
Local
catastrophes, like those which produce earthquakes, volcanoes, and other
particular causes are sufficiently well known, and it is possible to observe
the disorder which they bring about in the places which have experienced them.
But
why should anyone assume, without proof, a universal catastrophe, when the
better known progress of nature is sufficient to provide a reason for all the
facts which we observe in all its parts?
If one
considers, on the one hand, that in everything which nature brings about, she
make nothing abruptly and everywhere works slowly and by successive degrees
and, on the other hand, that the particular or local causes of disorders,
revolutions, displacements, and so on, can provide reasons for everything which
we observe on the surface of the earth and are nonetheless subject to nature’s
laws and her general progress, one will recognize that it is not at all
necessary to assume that a universal catastrophe came to knock over everything
and destroy a large part of the very operations of nature.
That
is enough on an issue which is readily comprehensible. Let us now consider the
general features and the essential characteristics of animals.
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