Lamarck, the Founder of Evolution Part 23

"4. Finally, how this organic movement, by the influence of its duration and by that of the mult.i.tude of circ.u.mstances which modify its effects, develops, arranges, and gradually complicates the organs of the living body which possesses them.

"Such has been without doubt the will of the infinite wisdom which reigns throughout nature; and such is effectively the order of things clearly indicated by the observation of all the facts which relate to them." (End of the opening discourse.)

APPENDIX (p. 141).

_On Species in Living Bodies._

"I have for a long time thought that _species_ were constant in nature, and that they were const.i.tuted by the individuals which belong to each of them.

"I am now convinced that I was in error in this respect, and that in reality only individuals exist in nature.

"The origin of this error, which I have shared with many naturalists who still hold it, arises from _the long duration_, in relation to us, _of the same state of things_ in each place which each organism inhabits; but this duration of the same state of things for each place has its limits, and with much time it makes changes in each point of the surface of the globe, which produces changes in every kind of circ.u.mstances for the organisms which inhabit it.

"Indeed, we may now be a.s.sured that nothing on the surface of the terrestrial globe remains in the same state. Everything, after a while, undergoes different changes, more or less prompt, according to the nature of the objects and of circ.u.mstances. Elevated areas are constantly being lowered, and the loose material carried down to the lowlands. The beds of rivers, of streams, of even the sea, are gradually removed and changed, as also the climate;[167] in a word, the whole surface of the earth gradually undergoes a change in situation, form, nature, and aspect. We see on every hand what ascertained facts prove; it is only necessary to observe and to give one's attention to be convinced of it.

"However, if, relatively to living beings, the diversity of circ.u.mstances brings about for them a diversity of habits, a different mode of existence, and, as the result, modifications in their organs and in the shape of their parts, one should believe that very gradually every living body whatever would vary in its organization and its form.

"All the modifications that each living being will have undergone as the result of change of circ.u.mstances which have influenced its nature will doubtless be propagated by heredity (_generation_). But as new modifications will necessarily continue to operate, however slowly, not only will there continually be found new species, new genera, and even new orders, but each species will vary in some part of its structure and its form.

"I very well know that to our eyes there seems in this respect a _stability_ which we believe to be constant, although it is not so truly; for a very great number of centuries may form a period insufficient for the changes of which I speak to be marked enough for us to appreciate them. Thus we say that the flamingo (_Phoenicopterus_) has always had as long legs and as long a neck as have those with which we are familiar; finally, it is said that all animals whose history has been transmitted for 2,000 or 3,000 years are always the same, and have lost or acquired nothing in the process of perfection of their organs and in the form of their different parts. We may be a.s.sured that this appearance of _stability_ of things in nature will always be taken for reality by the average of mankind, because in general it judges everything only relatively to itself.

"But, I repeat, this consideration which has given rise to the admitted error owes its source to the very great slowness of the changes which have gone on. A little attention given to the facts which I am about to cite will afford the strongest proof of my a.s.sertion.

"What nature does after a great length of time we do every day by suddenly changing, as regards a living being, the circ.u.mstances in which it and all the individuals of its species are placed.

"All botanists know that the plants which they transplant from their natal spot into gardens for cultivation there gradually undergo changes which in the end render them unrecognizable. Many plants naturally very hairy, there become glabrous or nearly so; a quant.i.ty of those which were proc.u.mbent or trailing there have erect stems; others lose their spines or their thorns; finally, the dimensions of parts undergo changes which the circ.u.mstances of their new situation infallibly produce. This is so well known that botanists prefer not to describe them, at least unless they are newly cultivated. Is not wheat (_Tritic.u.m sativum_) a plant brought by man to the state wherein we actually see it, which otherwise I could not believe? Who can now say in what place its like lives in nature?

"To these known facts I will add others still more remarkable, and which confirm the view that change of circ.u.mstances operates to change the parts of living organisms.

"When _Ranunculus aquatilis_ lives in deep water, all it can do while growing is to make the end of its stalks reach the surface of the water where they flourish. Then all the leaves of the plant are finely cut or pinked.[168] If the same plant grows in shallower water the growth of its stalks may give them sufficient extent for the upper leaves to develop out of the water; then its lower leaves only will be divided into hair-like joints, while the upper ones will be simple, rounded, and a little lobed.[169] This is not all: when the seeds of the same plant fall into some ditch where there is only water or moisture sufficient to make them germinate, the plant develops all its leaves in the air, and then none of them is divided into capillary points, which gives rise to _Ranunculus hederaceus_, which botanists regard as a species.

"Another very striking proof of the effect of a change of circ.u.mstances on a plant submitted to it is the following:

"It is observed that when a tuft of _Juncus bufonius_ grows very near the edge of the water in a ditch or marsh this rush then pushes out filiform stems which lie in the water, are there deformed, becoming disturbed (_tracantes_), proliferous, and very different from that of _Juncus bufonius_ which grows out of water. This plant, modified by the circ.u.mstances I have just indicated, has been regarded as a distinct species; it is the _Juncus supinus_ of Rotte.[170]

"I could also give citations to prove that the changes of circ.u.mstances relative to organisms necessarily change the influences which they undergo on the part of all that which environs them or which acts on them, and so necessarily bring about changes in their size, their shape, their different organs.

"Then among living beings nature seems to me to offer in an absolute manner only individuals which succeed one another by generation.

"However, in order to facilitate the study and recognition of these organisms, I give the name of _species_ to every collection of individuals which during a long period resemble each other so much in all their parts that these individuals only present small accidental differences which, in plants, reproduction by seeds causes to disappear.

"But, besides that at the end of a long period the totality of individuals of such a species change as the circ.u.mstances which act on them, those of these individuals which from special causes are transported into very different situations from those where the others occur, and then constantly submitted to other influences--the former, I say, a.s.sume new forms as the result of a long habit of this other mode of existence, and then they const.i.tute a new _species_, which comprehends all the individuals which occur in the same condition of existence. We see, then, the faithful picture of that which happened in this respect in nature, and of that which the observation of its acts can alone discover to us."

III. _Lamarck's Views on Species, as published in 1803._

In the opening lecture[171] of his course at the Museum of Natural History, delivered in prairial (May 20-June 18), 1803, we have a further statement of the theoretical views of Lamarck on species and their origin. He addresses his audience as "Citoyens," France still being under the _regime_ of the Republic.

The brochure containing this address is exceedingly rare, the only copy existing, as far as we know, being in the library of the Museum of Natural History in Paris. The author's name is not even given, and there is no imprint. Lamarck's name, however, is written on the outside of the cover of the copy we have translated. At the end of the otherwise blank page succeeding the last page (p. 46) is printed the words: _Esquisse d'un Philosophie zoologique_, the preliminary sketch, however, never having been added.

He begins by telling his hearers that they should not desire to burden their memories with the infinite details and immense nomenclature of the prodigious quant.i.ty of animals among which we distinguish an illimitable number of species, "but what is more worthy of you, and of more educational value, you should seek to know the course of nature."

"You may enter upon the study of cla.s.ses, orders, genera, and even of the most interesting species, because this would be useful to you; but you should never forget that all these subdivisions, which could not, however, be well spared, are artificial, and that nature does not recognize any of them."

"In the opening lecture of my last year's course I tried to convince you that it is only in the organization of animals that we find the foundation of the natural relations between the different groups, where they diverge and where they approach each other. Finally, I tried to show you that the enormous series of animals which nature has produced presents, from that of its extremities where are placed the most perfect animals, down to that which comprises the most imperfect, or the most simple, an evident modification, though irregularly defined (_nuance_), in the structure of the organization.

"To-day, after having recalled some of the essential considerations which form the base of this great truth; after having shown you the princ.i.p.al means by which nature is enabled to create (_operer_) her innumerable productions and to vary them infinitely; finally, after having made you see that in the use she has made of her power of generating and multiplying living beings she has necessarily proceeded from the more simple to the more complex, gradually complicating the organization of these bodies, as also the composition of their substance, while also in that which she has done on non-living bodies she has occupied herself unremittingly in the destruction of all preexistent combinations, I shall undertake to examine under your eyes the great question in natural history--What is a _species_ among organized beings?

"When we consider the series of animals, beginning at the end comprising the most perfect and complicated, and pa.s.sing down through all the degrees of this series to the other end, we see a very evident modification in structure and faculties. On the contrary, if we begin with the end which comprises animals the most simple in organization, the poorest in faculties and in organs--in a word, the most imperfect in all respects--we necessarily remark, as we gradually ascend in the series, a truly progressive complication in the organization of these different animals, and we see the organs and faculties of these beings successively multiplying and diversifying in a most remarkable manner.

"These facts once known present truths which are, to some extent, eternal; for nothing here is the product of our imagination or of our arbitrary principles; that which I have just explained rests neither on systems nor on any hypothesis: it is only the very simple result of the observation of nature; hence I do not fear to advance the view that all that one can imagine, from any motives whatever, to contradict these great verities will always be destroyed by the evidence of the facts with which it deals.

"To these facts it is necessary to add these very important considerations, which observation has led me to perceive, and the basis of which will always be recognized by those who pay attention to them; they are as follows:

"Firstly, the exercise of life, and consequently of organic movement, const.i.tutes its activity, tends, without ceasing, not only to develop and to extend the organization, but it tends besides to multiply the organs and to isolate them in special centres (_foyers_). To make sure whether the exercise of life tends to extend and develop the organization, it suffices to consider the state of the organs of any animal which has just been born, and to compare them in this condition with what they are when the animal has attained the period when its organs cease to receive any new development. Then we will see on what this organic law is based, which I have published in my _Recherches sur les Corps vivans_ (p. 8), _i.e._, that--

"'The special property of movement of fluids in the supple parts of the living body which contain them is to open (_frayer_) there routes, places of deposit and tissues; to create there ca.n.a.ls, and consequently different organs; to cause these ca.n.a.ls and these organs to vary there by reason of the diversity both of the movements as well as the nature of the fluids which occur there; finally to enlarge, to elongate, to divide and to gradually strengthen (_affermir_) these ca.n.a.ls and their organs by the matters which are formed in the fluids in motion, which incessantly separate themselves, and a part of which is a.s.similated and united with organs while the rest is rejected.'

"Secondly, the continual employment of an organ, especially if it is strongly exercised, strengthens this organ, develops it, increases its dimensions, enlarges and extends its faculties.

"This second law of effects of exercise of life has been understood for a long time by those observers who have paid attention to the phenomena of organization.

"Indeed, we know that all the time that an organ, or a system of organs, is rigorously exercised throughout a long time, not only its power, and the parts which form it, grow and strengthen themselves, but there are proofs that this organ, or system of organs, at that time attracts to itself the princ.i.p.al active forces of the life of the individual, because it becomes the cause which, under these conditions, makes the functions of other organs to be diminished in power.

"Thus not only every organ or every part of the body, whether of man or of animals, being for a long period and more vigorously exercised than the others, has acquired a power and facility of action that the same organ could not have had before, and that it has never had in individuals which have exercised less, but also we consequently remark that the excessive employment of this organ diminishes the functions of the others and proportionately enfeebles them.

"The man who habitually and vigorously exercises the organ of his intelligence develops and acquires a great facility of attention, of apt.i.tude for thought, etc., but he has a feeble stomach and strongly limited muscular powers. He, on the contrary, who thinks little does not easily, and then only momentarily fixes his attention, while habitually giving much exercise to his muscular organs, has much vigor, possesses an excellent digestion, and is not given to the abstemiousness of the savant and man of letters.

"Moreover, when one exercises long and vigorously an organ or system of organs, the active forces of life (in my opinion, the nervous fluid) have taken such a habit of acting (_porter_) towards this organ that they have formed in the individual an inclination to continue to exercise which it is difficult for it to overcome.

"Hence it happens that the more we exercise an organ, the more we use it with facility, the more does it result that we perceive the need (_besoin_) of continuing to use it at the times when it is placed in action. So we remark that the habit of study, of application, of work, or of any other exercise of our organs or of any one of our organs, becomes with time an indispensable need to the individual, and often a pa.s.sion which it does not know how to overcome.

"Thirdly, finally, the effort made by necessity to obtain new faculties is aided by the concurrence of favorable circ.u.mstances; they create (_creent_) with time the new organs which are adapted (_propres_) to their faculties, and which as the result develop after long use (_qu'en suite un long emploi developpe_).

"How important is this consideration, and what light it spreads on the state of organization of the different animals now living!

"a.s.suredly it will not be those who have long been in the habit of observing nature, and who have followed attentively that which happens to living individuals (to animals and to plants), who will deny that a great change in the circ.u.mstances of their situation and of their means of existence forces them and their race to adopt new habits; it will not be those, I say, who attempt to contest the foundation of the consideration which I have just exposed.

"They can readily convince themselves of the solidity of that which I have already published in this respect.[172]

"I have felt obliged to recall to you these great considerations, a sketch of which I traced for you last year, and which I have stated for the most part in my different works, because they serve, as you have seen, as a solution of the problem which interests so many naturalists, and which concerns the determination of _species_ among living bodies.

"Indeed, if in ascending in the series of animals from the most simply organized animalcule, as from the monad, which seems to be only an animated point, up to the animals the most perfect, or whose structure is the most complicated--in a word, up to animals with mammae--you observe in the different orders which comprise this great series a gradation, shaded (_nuance_), although irregular, in the composition of the organization and in the increasing number of faculties, is it not evident that in the case where nature would exert some active power on the existence of these organized bodies she has been able to make them exist only by beginning with the most simple, and that she has been able to form directly among the animals only that which I call the rough sketches or germs (_ebauches_) of animality--that is to say, only these animalcules, almost invisible and to some extent without consistence, that we see develop spontaneously and in an astonishing abundance in certain places and under certain circ.u.mstances, while only in contrary circ.u.mstances are they totally destroyed?

"Do we not therefore perceive that by the action of the laws of organization, which I have just now indicated, and by that of different means of multiplication which are due to them (_qui en derivent_), nature has in favorable times, places, and climates multiplied her first germs (_ebauches_) of animality, given place to developments of their organizations, rendered gradually greater the duration of those which have originally descended from them, and increased and diversified their organs? Then always preserving the progress acquired by the reproductions of individuals and the succession of generations, and aided by much time and by a slow but constant diversity of circ.u.mstances, she has gradually brought about in this respect the state of things which we now observe.

"How grand is this consideration, and especially how remote is it from all that is generally thought on this subject! Moreover, the astonishment which its novelty and its singularity may excite in you requires that at first you should suspend your judgment in regard to it. But the observation which establishes it is now on record (_consignee_), and the facts which support it exist and are incessantly renewed; however, as they open a vast field to your studies and to your own researches, it is to you yourselves that I appeal to p.r.o.nounce on this great subject when you have sufficiently examined and followed all the facts which relate to it.