Evolution, Old & New Part 20

[190] 'Hist, des Anim. sans Verteb.,' tom, i., Introduction, 1^re ed., 1815; 'Syst. des Conn. Positives,' Paris, in-8, 1820, 1^re part, 2^me sect. ch. ii. p. 114, &c.

[191] 'Hist. Nat. Gen.,' tom. ii. p. 407.

[192] 'History of Creation,' English translation, vol. i. pp. 111, 112.

[193] M. Martins' edition of the 'Philosophie Zoologique,' Paris, 1873.

Introd., p. vi.

[194] 'Origin of Species,' p. 3, 1859.

[195] 'Vestiges of Creation,' ed. 1860, Proofs, Ill.u.s.trations, &c., p.

lxiv.

[196] 'Origin of Species,' ed. 1, p. 239; ed. 6, p. 231.

[197] 'Origin of Species,' ed. 1, p. 242; ed. 6, 1876, p. 233.

[198] 'Origin of Species,' p. 421, ed. 1876.

[199] 'Phil. Zool.,' vol. i. p. 404.

[200] Ibid. vol. ii. p. 324.

[201] 'Phil. Zool.,' vol. ii. p. 410.

[202] 'Les Amours des Plantes,' Discours Prelim., p. 7. Paris, 1800.

[203] Ibid., Notes du chant i., p. 202.

[204] Ibid. p. 238.

[205] 'Zoonomia,' vol. i. p. 507.

[206] 'Les Amours des Plantes,' p. 360.

[207] Vol. i. p. 231, ed. M. Martins, 1873.

CHAPTER XVII.

SUMMARY OF THE 'PHILOSOPHIE ZOOLOGIQUE.'

The first part of the '_Philosophie Zoologique_' is the one which deals with the doctrine of evolution or descent with modification. It is to this, therefore, that our attention will be confined. Yet only a comparatively small part of the three hundred and fifty pages which const.i.tute Lamarck's first part are devoted to setting forth the reasons which led him to arrive at his conclusions--the greater part of the volume being occupied with the cla.s.sification of animals, which we may again omit, as foreign to our purpose.

I shall condense whenever I can, but I do not think the reader will find that I have left out much that bears upon the argument. I shall also use inverted commas while translating with such freedom as to omit several lines together, where I can do so without suppressing anything essential to the elucidation of Lamarck's meaning. I shall, however, throughout refer the reader to the page of the original work from which I am translating.

"The common origin of bodily and mental phenomena," says Lamarck in his preliminary chapter, "has been obscured, because we have studied them chiefly in man, who, as the most highly developed of living beings, presents the problem in its most difficult and complicated aspect. If we had begun our study with that of the lowest organisms, and had proceeded from these to the more complex ones, we should have seen the progression which is observable in organization, and the successive acquisition of various special organs, with new faculties for every additional organ.

We should thus have seen that sense of needs--originally hardly perceptible, but gradually increasing in intensity and variety--has led to the attempt to gratify them; that the actions thus induced, having become habitual and energetic, have occasioned the development of organs adapted for their performance; that the force which excites organic movements can in the case of the lowest animals exist outside them and yet animate them; that this force was subsequently introduced into the animals themselves, and fixed within them; and, lastly, that it gave rise to sensibility and, in the end, to intelligence."[208] The reader had better be on his guard here, and whenever Lamarck is speculating about the lowest forms of action and sensation. I have thought it well, however, to give enough of these speculations, as occasion arises, to show their tendency.

"Sensation is not the proximate cause of organic movements. It may be so with the higher animals, but it cannot be shown to be so with plants, nor even with all known animals. At the outset of life there was none of that sensation which could only arise where organic beings had already attained a considerable development. Nature has done all by slow gradations, both organs and faculties being the outcome of a progressive development.[209]

"The mere composition of an animal is but a small part of what deserves study in connection with the animal itself. The effects of its surroundings in causing new wants, the effects of its wants in giving rise to actions, those of its actions in developing habits and tendencies, the effects of use and disuse as affecting any organ, the means which nature takes to preserve and make perfect what has been already acquired--these are all matters of the highest importance.[210]

"In their bearing upon these questions the invertebrate animals are more important and interesting than the vertebrate, for they are more in number, and being more in number are more varied; their variations are more marked, and the steps by which they have advanced in complexity are more easily observed.[211]

"I propose, therefore, to divide this work into three parts, of which the first shall deal with the conventions necessary for the treatment of the subject, the importance of a.n.a.logical structures, and the meaning which should be attached to the word species. I will point out on the one hand the evidence of a graduated descending scale, as existing between the highest and the lowest organisms; and, on the other, the effect of surroundings and habits on the organs of living beings, as the cause of their development or arrest of development. Lastly, I will treat of the natural order of animals, and show what should be their fittest cla.s.sification and arrangement."[212]

It seems unnecessary to give Lamarck's intentions with regard to his second and third parts, as they do not here concern us; they deal with the origin of life and mind.

The first chapter of the work opens with the importance of bearing in mind the difference between the conventional and the natural, that is to say, between words and things. Here, as indeed largely throughout this part of his work, he follows Buffon, by whom he is evidently influenced.

"The conventional deals with systems of arrangement, cla.s.sification, orders, families, genera, and the nomenclature, whether of different sections or of individual objects.

"An arrangement should be called systematic, or arbitrary, when it does not conform to the genealogical order taken by nature in the development of the things arranged, and when, by consequence it is not founded upon well-considered a.n.a.logies. There is such a thing as a natural order in every department of nature; it is the order in which its several component items have been successively developed.[213]

"Some lines certainly seem to have been drawn by Nature herself. It was hard to believe that mammals, for example, and birds, were not well-defined cla.s.ses. Nevertheless the sharpness of definition was an illusion, and due only to our limited knowledge. The ornithorhynchus and the echidna bridge the gulf.[214]

"Simplicity is the main end of any cla.s.sification. If all the races, or as they are called, species, of any kingdom were perfectly known, and if the true a.n.a.logies between each species, and between the groups which species form, were also known, so that their approximations to each other and the position of the several groups were in conformity with the natural a.n.a.logies between them--then cla.s.ses, orders, sections, and genera would be families, larger or smaller; for each division would be a greater or smaller section of a natural order or sequence.[215] But in this case it would be very difficult to a.s.sign the limits of each division; they would be continually subjected to arbitrary alteration, and agreement would only exist where plain and palpable gaps were manifest in our series. Happily, however, for cla.s.sifiers there are, and will always probably remain, a number of unknown forms."[216]

That the foregoing is still felt to be true by those who accept evolution, may be seen from the following pa.s.sage, taken from Mr.

Darwin's 'Origin of Species':--

"As all the organic beings which have ever lived can be arranged within a few great cla.s.ses; and as all within each cla.s.s have, according to our theory, been connected together by fine gradations, the best, and if our collections were nearly perfect, the only possible arrangement would be genealogical: descent being the hidden bond of connection which naturalists have been seeking under the term of the Natural System. On this view, we can understand how it is that in the eyes of most naturalists, the structure of the embryo is even more important for cla.s.sifications than that of the adult."[217]

In his second chapter Lamarck deals with the importance of comparative anatomy, and the study of h.o.m.ologous structures. These indicate a sort of blood relationship between the individuals in which they are found, and are our safest guide to any natural system of cla.s.sification. Their importance is not confined to the study of cla.s.ses, families, or even species; they must be studied also in the individuals of each species, as it is thus only, that we can recognize either ident.i.ty or difference of species. The results arrived at, however, are only trustworthy over a limited period, for though the individuals of any species commonly so resemble one another at any given time, as to enable us to generalize from them, at the date of our observing them, yet species are not fixed and immutable through all time: they change, though with such extreme slowness that we do not observe their doing so, and when we come upon a species that _has_ changed, we consider it as a new one, and as having always been such as we now see it.[218]

"It is none the less true that when we compare the same kind of organs in different individuals, we can quickly and easily tell whether they are very like each other or not, and hence, whether the animals or plants in which they are found, should be set down as members of the same or of a different species. It is only therefore the general inference drawn from the apparent immutability of species, that has been too inconsiderately drawn.[219]

"The a.n.a.logies and points of agreement between living organisms, are always incomplete when based upon the consideration of any single organ only. But though still incomplete, they will be much more important according as the organ on which they are founded is an essential one or otherwise.

"With animals, those a.n.a.logies are most important which exist between organs most necessary for the conservation of their life. With plants, between their organs of generation. Hence, with animals, it will be the interior structure which will determine the most important a.n.a.logies: with plants it will be the manner in which they fructify.[220]

"With animals we should look to nerves, organs of respiration, and those of the circulation; with plants, to the embryo and its accessories, the s.e.xual organs of their flowers, &c.[221] To do this, will set us on to the Natural Method, which is as it were a sketch traced by man of the order taken by Nature in her productions.[222] Nevertheless the divisions which we shall be obliged to establish, will still be arbitrary and artificial, though presenting to our view sections arranged in the order which Nature has pursued.[223]

"What, then," he asks,[224] "_is_ species--and can we show that species has changed--however slowly?" He now covers some of the ground since enlarged upon in Mr. Darwin's second chapter, in which the arbitrary nature of the distinction between species and varieties is so well exposed. "I shall show," says Lamarck (in substance, but I am compelled to condense much), "that the habits by which we now recognize any species, are due to the conditions of life [_circonstances_] under which it has for a long time existed, and that these habits have had such an influence upon the structure of each individual of the species, as to have at length modified this structure, and adapted it to the habits which have been contracted.[225]

"The individuals of any species," he continues, "certainly resemble their parents; it is a universal law of nature that all offspring should differ but little from its immediate progenitors, but this does not justify the ordinary belief that species never vary. Indeed, naturalists themselves are in continual difficulty as regards distinguishing species from varieties; they do not recognize the fact that species are only constant as long as the conditions in which they are placed are constant. Individuals vary and form breeds which blend so insensibly into the neighbouring species, that the distinctions made by naturalists between species and varieties, are for the most part arbitrary, and the confusion upon this head is becoming day by day more serious.[226]

"Not perceiving that species will not vary as long as the conditions in which they are placed remain essentially unchanged, naturalists have supposed that each species was due to a special act of creation on the part of the Supreme Author of all things. a.s.suredly, nothing can exist but by the will of this Supreme Author, but can we venture to a.s.sign rules to him in the execution of his will? May not his infinite power have chosen to create an order of things which should evolve in succession all that we know as well as all that we do not know? Whether we regard species as created or evolved, the boundlessness of his power remains unchanged, and incapable of any diminution whatsoever. Let us then confine ourselves simply to observing the facts around us, and if we find any clue to the path taken by Nature, let us say fearlessly that it has pleased her Almighty Author that she should take this path.[227]

"What applies to species applies also to genera; the further our knowledge extends, the more difficult do we find it to a.s.sign its exact limits to any genus. Gaps in our collections are being continually filled up, to the effacement of our dividing lines of demarcation. We are thus compelled to settle the limits of species and variety arbitrarily, and in a manner about which there will be constant disagreement. Naturalists are daily cla.s.sifying new species which blend into one another so insensibly that there can hardly be found words to express the minute differences between them. The gaps that exist are simply due to our not having yet found the connecting species.

"I do not, however, mean to say that animal life forms a simple and continuously blended series. Life is rather comparable to a ramification. In life we should see, as it were, a ramified continuity, if certain species had not been lost. The species which, according to this ill.u.s.tration, stands at the extremity of each bough, should bear a resemblance, at least upon one side, to the other neighbouring species; and this certainly is what we observe in nature.

"Having arranged living forms in such an order as this, let us take one, and then, pa.s.sing over several boughs, let us take another at some distance from it; a wide difference will now be seen between the species which the forms selected represent. Our earliest collections supplied us with such distantly allied forms only; now, however, that we have such an infinitely greater number of specimens, we can see that many of them blend one into the other without presenting noteworthy differences at any step."[228]