It is, in more scientific terms, the definition by Lamarck, “a collection of similar individuals which generation perpetuates in the same state, so that the circumstances of their situation do not sufficiently alter so as to make their habits, their character, or their form vary.”[295] Lamarck, to whom Isidore Geoffroy has rendered greater justice than any one else before or after him,[296] admitted the unlimited variableness of species. He admitted that we all descend, just as we are, from an anatomical element, developed in a determinate sense, and that we may have been worms, insects,[297] birds, and mammals before becoming men, running through all the phases through which animal organisation has passed during our uterine life. We see that Lamarck approached frankly and resolutely the problem of the origin of humanity.
In taking but superficially certain exaggerations into which Lamarck fell, at a time less rich in facts than our own, it is not difficult to give a certain grotesque turn to his ideas, and to laugh at them as being unnatural; but we must not thus judge the work of a man’s whole life, and we must appreciate Lamarck by the basis of his doctrine more than by the examples he has given us: “a profound philosopher,” said Étienne Geoffroy,[298] “able in laying down principles, less able in the choice of his proofs.”
We must judge Lamarck as Isidore Geoffroy has done in his Histoire Naturelle Générale, where we find a complete and impartial chronological statement concerning the grave question of species.[299] “Circumstances have an influence upon form and organisation,” such is the fundamental principle of Lamarck’s doctrine;[300] he says the same elsewhere:[301] “Circumstances determine positively what each body may be;” and he concludes, “among living bodies, nature only shows individuals who succeed one another. Species, amongst themselves, are only relative, and are only temporarily so.”[302]
If from these general considerations we enter in detail into Lamarck’s theory, we find room for the objections with which the opponents of the system of variety are engrossed, with which they have made those weapons of ridicule which act so well on minds which are not forewarned, and who are ignorant of this master’s whole system of ideas. The grandeur of Lamarck’s views, the majestic simplicity of his theory, ought to be sufficient to shield him from such attacks. He saw at the beginning organic matter grouping itself under simple forms. These first outlines, altered by time and circumstances, have successively given birth to radiated creatures, to the inferior molluscs, the articulate animals, then the lowest fishes, then man.
Here is a mistake, in our opinion; if there exists (until we know more) an immense and impassable difference somewhere in the animal kingdom, it is between the vertebrate and the invertebrate animals. Whilst the first show an admirable unity of organic composition, the second do not seem to have any at all, so that they do not admit of serial or linear classification. Each of the groups which they form is united by some particularity to all the other groups, and naturalists have even been able to differ about what must be considered as the highest round in the animal ladder. The organism of the invertebrata possesses a flexibility and immense variety, which is almost a characteristic special to these beings in which the nervous system ceases to present the profound unity which we see in the vertebrata; whilst the entire group has only a negative characteristic, the want of vertebræ, which is sufficient alone to show how unnatural it is. As for the rest, the vertebrate animal, even at the first moment of his embryo life, is absolutely irreducible to any invertebrate type whatsoever, contrary to Lamarck’s opinion. A vertebrate is to an invertebrate as two first numbers are to one another; all the vertebrata, on the contrary, are one to another as a simple number raised to different powers; they can all be brought back to their origin, and both the most complicated and the most elevated of the series are only the most simple ones arrived at a state of considerable perfection.
A still weaker side of Lamarck’s theory is certainly the decided influence which he attributes to the actions and habits of organised beings, so as to modify them by their own means. The pedantic caprice of his enemies has always hit on this point. “The habit of exercising an organ,” he says, “makes it acquire developments and dimensions which insensibly change it, so that in time it becomes very different. On the contrary, the faulty continual exercise of an organ impoverishes it gradually, and ends by destroying it.”[303] But it must not be thought that Lamarck gave an appreciable alteration to the organ,—an alteration sufficiently rapid to be noticed by ourselves. If some passages of his works make the reader think so, it is plain that they are only the wanderings of a great mind, always weak on the side of the ideas which he has created, and which he cherishes. Lamarck knew very well that an infinite time is the condition of unlimited variability.[304]
Darwin is the direct successor of Lamarck, and, in our opinion, the success of his book both in England and France is an index of the progress which scientific ideas have made, since the days of Cuvier, in the path of liberty and independence. Darwin, like Lamarck, admits unlimited variety; he thinks that all animals must descend from four or five primitive types, and plants from about an equal number; he is almost disposed to admit but one primordial type for all organic nature.[305]
Darwin, however, seems to us to have fallen into a grievous exaggeration, or error of interpretation, formerly laid to Lamarck’s charge, while he is at the same time defending an excellent cause. Without speaking here of the relationship (forced, in our opinion) which Darwin makes out between wild and domestic animals (of which we have before spoken), the learned Englishman seems to have accorded too much to individual action in the production of specific modification. He sees a powerful activity, which he calls natural selection, where we can only see absolute passiveness. We will explain what we mean: in the midst of this vital concurrence, which he has in part so well described,—in the midst of this immense struggle, where all which has life on our planet is engaged in combat one against the other, or against all, on this eternal field of battle, where the victors become the victims, Darwin supposes that an animal brings into the world with him, by chance, some psychological modification, or some anatomical disposition, which is individually advantageous to him in the great struggle for life; after this he will have a chance of being among the victors, of uniting himself to another animal as happily endowed by birth by having also conquered; they will together leave a numerous posterity, and there is every chance that some of the descendants of such a couple may inherit either the same instinctive disposition or the same conformation; definitively, and by the repeated action of this natural proceeding, a new variety can be formed, and may either supplant the parent species or coexist with it.[306]
Such is, in a few words, the theory of natural selection. In our ideas, there is here a false interpretation of facts; we do not believe in this chance of a native disposition, which thus transmits itself in order to become in time a specific characteristic. We have shown, while speaking of hybridity, that a native individual disposition ought always to disappear by the mere fact of its being individual; it quickly disappears through cross-breeding at the tenth generation, if not at the first, in the midst of a population which does not possess it. We fully admit, like Lamarck, that species are formed from one another by the appearance of organic modifications, more or less decided; but we do not leave anything to chance in this phenomenon, as Darwin does, and we can only see there the application of general laws.
It is not one or two animals, born with some special psychological or anatomical disposition, who are destined to generalise themselves by generation: it will be all the individuals of the same species in a certain radius, who will be born with a scarcely appreciable organic modification, resulting, as far as we can tell, in an action of the medium also nearly inappreciable by ourselves, but which long ago will have made itself felt by the parents. The new variety will be propagated quite naturally, since it is general, and can but increase with each generation as long as the modifying cause continues to act.