Popular Science Monthly/Volume 23/August 1883/Perrier on the Theory of Descent
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Perrier on the Theory of Descent
By Alfred Victor Espinas
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By M. A. ESPINAS.
THE preface of twenty pages with which M. Edmond Perrier has introduced M. Leveque's French translation of Mr. Darwin's essay on "Earth-Worms" is a masterly work, the importance of which will escape no one. We know that this eminent naturalist, after having given a quite cool reception to the theory of descent, at last, in his "Colonies Animales," accepted it, under reserves, the tendency of which was to restrict the bearing of evolution at different points. First, he denied that that theory could explain the passage from the P EERIER ON THE THEORY OF DESCENT. 525
inorganic to the organic. Secondly, he refused to account, by it alone, that is, by the combined action of the environment and of heredity, for living forms ; but had recourse, to explain some among them, to an internal nisus, or an original preformation analogous to final causes. Lastly, he believed that the general laws of evolution expired in some way at the threshold of the human world, and that human consciousness is formed after other laws than the organic consensus. It was the part of philosophy, now in possession of an idea of science which it owes largely to the scientific men themselves, to indicate these later reserves. For it is, after all, no small matter to know what is of science and what is not. It is imperatively necessary for us to fix our eyes on this capital point, and to decide among ourselves whether those who in their researches accord a part to final causes, and attribute an excep- tional position in nature to man, are performing a work of science or of metaphysics. This is why, without losing sight of the rare merits of the work we have named, we have thought it proper to point out the ambiguous character of some parts of it.
Now, M. Perrier has resolutely canceled most of his reserves. The second part of his preface, in which he for the first time traces the geographical distribution of the species of terrestrial lumbrici, and points out the consequences of such distribution both in respect to specific characteristics and from the geological point of view, is out of our province to consider. The first part, which is devoted to a gen- eral appreciation of Darwin's work, has a high philosophical signifi- cance ; and we here give a summary of the whole of it.
" Until within the last twenty years," says the author, " living beings were nearly always studied independently of the medium in which they live and of the relations which they form with each other. Each of them appeared to be a distinct entity, owing nothing except to itself, capable of abstracting itself from every modifying action on the part of external agents, created once for all in view of certain con- ditions of existence, marvelously adapted to these conditions, but unable to extricate itself from them except at the cost of perishing, in perfect equilibrium with the supposed unchangeable medium, but destined to disappear whenever the equilibrium was broken. This false conception of the living being has caused the failure of every essay at a philosophy of the natural sciences which has been attempted till now."
M. Perrier then shows by a small number of selected examples that each being, under the pressure of variable circumstances is, aside from any preconceived plan, adapted to its environment, even when it may not have seemed primarily destined to live in it ; some fishes to a life in the air, some mammals and some birds to an aquatic life. He re- marks that the living beings of the environment are the preponderant part of the medium for each species. Adaptations not less close than those which unite organisms to the physical medium, put organisms in
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dependence, one upon another, and provoke morphological variations which wholly change the aspect of each one of them. " The probosces of bees and of butterflies would be useless to them if there existed no flowers." The teeth of mammals tell what their regimen is. All their structure is likewise derived and by a kind of reaction from it. " The tongue of the ant-bear and its enormous salivary glands can evidently be useful only for the capture of ants, termites, and other insects liv- ing in societies. There are insects that never come out of the ant- hills ; some of them are blind, and others can not eat anything but the food with which the ants gorge them." Innumerable parasites have been modified in a similar manner by the animal environment accidentally chosen by them ; and all, starting from very different points, have, under the empire of analogous conditions of existence, put on similar characters. It is Darwin's glory to have established that while the physical and organic mediums are incessantly changing and endlessly producing the most varied and most unforeseen condi- tions, there are none among them to which organisms have not been able to bend themselves with a flexibility almost without limits.
These relations of the being with its medium furnished " the most powerful arguments for the doctrine of final causes. For this doc- trine will hereafter be substituted a higher, a broader philosophy, a conception of the living world which will be wonderful only by its majestic simplicity. Every adaptation of a living being to a deter- mined mode of existence has become no longer only a marvel to ad- mire, but is also a problem to be resolved. This study, in fact, is that of the whole of natural history."
At this point is given a brilliant picture, in which, reviewing the great divisions of the animal kingdom, the author designates in each of the dominant forms of living beings the effect of the conditions of their existence. Every type, we may say, is thus formed by these con- ditions. To them must be attributed not only the variations in detail which only are commonly called adaptations, but the essential traits of the type, " due also to an anterior adaptation, the effects of which have been transmitted from more or less remote ancestors to their jjos- terity." It results from this that the characteristics proceeding from the most ancient adaptations should be and are the most widely spread. And, as it is precisely the degree of generality of a characteristic which gives it its methodical value (the most general have been called dominant by Cuvier), their order of subordination is simply their order of antiquity. "The classifications, of which the dryness was formerly legendary, thus become all-palpitating with historical inter- est," for they relate to us the series of conditions of which the animal kingdom is the work and the witness.
Must man be excepted from the general operation of these laws ? In no way. It is from the natural sciences thus renovated that we must demand, says M. Perrier, " an exact and scientific notion of the
�� � place of man in nature."Whatever emotion the application of the doctrine of evolution to the moral world may cause, and however grave may be the shock it inflicts on the edifice of beliefs, it should be accepted with confidence, for it is true, and the truth can not be wrong. Even if it exacts a transformation of the social order by transforming beliefs, it must be faced resolutely. The natural sciences thus impose themselves on the attention even of the statesman." It is necessary attentively to follow their progress, to measure the bearing of their discoveries, to study their actual or possible influence on current beliefs and ideas, and to endeavor to construct a new edifice all the more quickly as the bases of the old one appear to be seriously threatened.
These declarations deserve a hearing. They have a considerable importance, not only because they come from a naturalist whose works and position assure him one of the first places among the French scientific men of his generation, but also and especially because this naturalist is not suspected of any inconsiderate enthusiasm for the doctrine of evolution, and because he only yesterday was defending the beliefs we have spoken of against it. The honorable scruples which have kept him back seem at last to have yielded to the force of accumulated proofs: he lets fall the barriers which he seemed disposed to keep up between nature and man; he perceives that mechanism and science blend, and does not hesitate to say so. We expected nothing less from his clear-sightedness and his sincerity.—Translated for the Popular Science Monthly from the Revue Philosophique.
- One of these works, a study of the organization of worms, has been pronounced "admirable" by Mr. Darwin.