Goethe, the great poet, was never a declared advocate of organic transformation, although he discussed it during his last years under the influence of the French transformationists. E. von Baer, the celebrated founder of embryology, became, especially after Darwin, a convinced transformationist; indeed he came very near recognizing evolution as a universal process.

At the beginning and in the first half of the nineteenth century, the doctrine of organic evolution was developed by the scientists in France in a manner much more definite than in Germany. It is especially Lamarck who contributed the most to this development in his "Philosophie zoologique," 1809, and in some earlier essays (the first one is dated 1801). Discussing the idea of species, Lamarck directs special attention to the artificial nature of this idea; to the numerous transitions from one species to another; to the fact of varieties and the connection of these varieties with different external circumstances; to the short duration of the life of existent species so far as we can establish the stability of these species. These are the principal arguments which he presents in favor of transmutability of species. While insisting upon the slow but continuous evolution of the earth's surface, he gains a partial idea of the direct connection which exists between this evolution and that of the organic world. But it is especially in the exposition of the causes of organic evolution that the work of Lamarck presents an extraordinary originality; a part of his work which we can not discuss here.

Geoffrey Saint-Hilaire united with his theory of the unity of plan, the doctrine of organic transformism, attributing the cause of these transformations to the ambient world.

But while Lamarck and Geoffrey Saint-Hilaire represent the doctrine of transformism, the opposing doctrine, that of the creation of species, has nowhere found advocates more enthusiastic and distinguished than Cuvier and Agassiz.

When once this last doctrine had been expressly introduced into natural history by the Swedish naturalist Linnaeus, Cuvier set himself to demonstrate it by observed facts. In linking the doctrine of fixity of species to that of the successive revolutions of the globe, he taught a series of successive creations of species; but, according to him, some of these species are not exterminated by the revolutions, and there have always been migrations of some species that survived. Above all, Agassiz became the typical advocate of the creation theory, teaching that God produced, in different geological periods, organic species more and more perfect, which, once created, remained unchanged.

Auguste Comte, founder of the positivist philosophy, although a resolute advocate of the intellectual and social evolution-especially

evidenced in his celebrated law of three stages-also remained a declared opponent of organic transformation.

Finally, at the beginning of the second half of the nineteenth century, Darwin succeeded in definitely establishing the doctrine of organic transformation in his celebrated work, "Origin of Species," 1859. The arguments brought forward by Darwin in support of this doctrine are so numerous and for the most part so original that they place this scientist quite above Lamarck, and it is not at all astonishing to see that the doctrine of transformation was adopted by the scientific world only after his vigorous and decisive arguments were published. Just as remarkable as this reasoning is the theory of natural selection which Darwin proposed (at the same time as Wallace) to support his theory of the evolution of the organic world; but upon this point the principle of Lamarck is perhaps of equal importance with that of Darwin. Darwin also holds an important place in the development of the theory of intellectual and social evolution through his work on the origin of man, "The Descent of Man," 1871.

Before Darwin, the great English geologist, Lyell, definitely destroyed the theory of cataclysms in geology and introduced instead the theory of slow and continuous changes due to agents still in action to-day at the surface of the earth. But after the triumph of the Darwinian theory of transformation, the idea of evolution was definitely adopted by geologists in a more precise sense than that of Lyell.

It was only when the doctrine of organic transformation was proposed and elaborated by Lamarck and Darwin that the philosophers began to glimpse the universal importance of the principle of evolution. Herbert Spencer was the first to grasp this importance, and while giving the formula of a general law of evolution, he applied this formula to the entire field of empirical reality, and even to the totality of things in the universe, but he never tried to examine the conditions necessary to a total evolution of the world. Ed. Hartmann was the first among speculative philosophers to set forth clearly, in his celebrated "Philosophie des Unbewussten," 1869, the problem of the world evolution, and while determining some of the essential conditions of that evolution, to try to give for the first time a positive solution of this problem.

Finally, H. Bergson, in "L'Évolution Créatrice," 1907, tried to state the principle of world evolution as identical with that of organic evolution, and with the actual duration of psychic time. Thus Bergson's doctrine is an example of a phenomenon which is not at all rare in the history of general ideas, a universal truth which has been found and elaborated according to scientific research (Laplace, La

marck, Lyell, and Darwin are the four greatest scientists who devoted themselves to this research) ends by being proclaimed by a philosopher as, so to speak, a logical necessity.

As the present short outline of the historical development of the idea of evolution shows, this idea has been established much more by scientific research than by philosophic speculation. And while the inorganic evolution was recognized by some of the Greek philosophers and by Descartes and Kant, the idea of organic evolution was never an integral part of any of the great systems of philosophy, and no great philosopher before Darwin had recognized the general and universal bearing of the idea of evolution. It is a rather extraordinary fact that an idea of an eminently philosophic importance, such as the idea of universal evolution, should never have been recognized as such until after science had demonstrated itthis is a bit humiliating to philosophers; and it shows us that human knowledge, if it wishes to attain its total unity, must find its support and its inspiration as much in scientific research as in pure speculation.

THE HEREDITY OF ACQUIRED CHARACTERS.1

By L. CUENOT,

Professor of the College of Sciences at Nancy.

An acquired character is a modification appearing in a plant or an animal, at any age whatsoever, which is plainly the effect of an exterior and accidental cause, of such nature that if this cause had not intervened, the modification would certainly not have been produced. Acquired characters are legion. We will cite a few to fix our conception of them and to illustrate the definition: The immunity which follows an infectious disease; the sensibility to injections of equine serum which is exhibited by the Tartar peoples nourished by the milk and meat of the horse; the pigmentation of the bare parts of the human skin exposed to the action of the open air and especially of light rich in ultra-violet rays; an accidental mutilation; the modifications presented by plants of the plain when transplanted to Alpine regions; the enlargement and the strength of a muscle systematically exercised; everything which man learns during his lifetime, such as his language, his writing, any form of sport, etc. It is understood that an acquired character is just the difference between the normal condition, or the condition which served as the point of departure before the action of the modifying cause, and the new condition after the action of that cause.

In order to consider a character as acquired, it is necessary that the relation of cause to effect should be evident, either when the cause has been made to act experimentally, or when the observation of nature has been made with the care and exactness of an experiment (which is rare). It is well known that for a long time, until about 1883, it was believed without question that the acquired character was hereditary to a more or less marked degree; that is, that parents having acquired a certain thing would procreate a generation presenting more or less completely, at least in the shape of an indication or a rudiment, the acquired bodily modification, in the absence of the exterior cause which had produced it in the parents. Lamarck and his school made of this heredity of acquired

1 Translated by permission from the Revue Générale des Sciences, Oct. 15, 1921.

characters the pivotal point of their theory of evolution and of adaptation. Darwin and Herbert Spencer also fully accepted it. It is useless to insist on the capital importance of the phenomenon for the general explanation of adaptations. Without for the moment asking ourselves why, we can see that the reactions of the individual to any exterior action whatever have very generally an adaptive or protective value: A tanned skin is less penetrable by ultraviolet rays; immunity protects against a new attack of disease; a muscle, a joint, exercised within certain limits, functions more easily and more effectively than before the training. If the heredity of acquired characters exists, to however slight a degree, we possess the key to an enormous number of adaptations. If it does not exist, we must find other explanations.

This is not alone a question which interests speculative scholars isolated from the world; it is also a question of importance to society. When it is repeated to the public at large that the practice of sports, even to excess, prepares for vigorous new generations, the idea is certainly entertained that the "all-round athletes" or even those who are abnormally specialized by exercise, will bequeath to their descendants at least a rudiment of their acquired qualities. It is surely the opinion of breeders, who believe that the effects of the training of race horses, of the good or bad nutrition of cattle, are transmissible in certain measure.

3

It was not until 1883 that, for theoretical reasons whose value has not been diminished by time, Pflüger, on the one hand, and Weismann, on the other (Essay on Heredity, read at a public meeting when he was tendered the position of vice rector of the University of Freiburg, on June 21, 1883), were led to formally doubt this heredity. Weismann presented arguments of such force-he examined the whole question with so penetrating a critique-that it is only just to give him the credit for the change of opinion which dates from his lecture of 1883. But if he convinced many biologists, he encountered also unyielding opponents so powerful that for 37 years, in spite of numerous and remarkable researches, the heredity of acquired characters has remained a problem continually presented. It may be said that all the experimental proofs which have been contributed to the support of the transmission (E. Fischer, Standfuss, Kammerer, etc.) are mediocre and do not lead to conviction, or are susceptible of criticism and interpretations which weaken their demonstrative value, or, indeed, are frankly contradicted (as in the

Pflüger, Ueber den Einfluss der Schwerkraft auf die Theilung der Zellen und auf die Entwicklung des Embryo, Arch. f. Phys., t. XXXII, 1883, p. 68.

Weismann, Essais sur l'Hérédité et la sélection naturelle, trad. de Varigny, Paris,