Page:Catholic Encyclopedia, volume 5.djvu/734

 EVOLUTION

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EVOLUTION

stancy of species was universally acknowledged, and this all the more because it seemed to be con- nected with the first chapter of the Bible. Georges Louis Leclerc BufFon (1707-SS), the "suggestive" author of the "Histoire naturelle g^n^rale et particu- here", was the first to dispute the Linna-an dogma on scientific grounds. Till 1761 he had defended the theory of constancy, but he then became an extreme evolutionist, and finally held that through the direct influence of environment species could undergo mani- fold modifications of structure. Similar views were expressed by the German Gottfried Reinliold Tre- viranus in his work " Biologie oder Philosophic tier lebenden Xatur" (1S02), and by "the poet of evolu- tion", J. W. Goethe (17-19-1832). However, none of these men worked out the details of a definite theory. The same must be said of the grandfather of Charles Darwin, Erasmus Darwin (1731-1S02), physician, poet, and naturalist, the first who seems to have an- ticipated Lamarck's main views. " All animals un- dergo transformations which are in part produced by their own exertions in response to pleasures and pains, and many of these acquired forms and propensities are transmitted to their posterity" (Zoonomia, 1794). Jean-Baptiste de Lamarck (b. 17-14) was the scientific foimder of the modern theory of evolution and its spe- cial form, known as Lamarckism. At the age of forty-nine Lamarck was elected professor of inverte- brate zoologj' at the Jardin des Plantes (Paris). In 1819 he became completely blind, and died ten years later in great poverty and neglected bj' his contem- poraries, socially and scientifically. The main ideas of his theory are contained in his "Philosophic zoolo- gique" (1809) and liis "Histoire des animaux sans vertebres" (1816-22). Lamarck disputes the immu- tability of specific characters, and denies that there is any objective criterion for determining, with any de- gree of accuracy, W'hich forms ought to be considered as true species. Consequently, according to him, the name species has only a relative value. It refers to a collection of similar individuals " que la generation perpetuedans le meme etat tant que les circonstances tie leur situation ne changent pas assez pour fair varier Icurs habitudes, leur caractere et leur forme" (Phil, zool., I, p. 75). But how are species transformetl into new species? As to plants, Lamarck believes that all changes of structure antl function are due to the direct influence of environment. In animals the changed conditions of the environment first call forth new- wants and new acti\ities. New habits and instincts will be produced, and through use and disuse organs may be strengthenetl or weakened, newly adapteti to the requirements of new functions, or made to disap- pear. The acquiretl changes are handed flown to the offspring by the strong principle of inlieritance. Thus the web in the feet of water birtis was acquired through use, while the so-called rudimentarj' organs, e. g. the teeth of the baleen whale, the small eyes of the mole, were retluced to their imperfect condition through disuse. Lamarck did not mclude the origin of man in his system. He expressed his belief in abio- genesis, but he maintained at the same time that " rien n'existe que par la volonte du sublime Auteur de toutes choses" (Phil, zool., I, p. 56).

Lamarck's theorj' was not sufficiently supported by facts. Besides, it offereil no satisfactorj- explanation of the origin and development of new organs, though he did not ascribe the effect to a mere wish of the ani- mal. Finally, he offered no proof whatever for his position that acquired characters are inheritetl. La- marck had very little influence upon his own time. Shortly after his tlealh the famous discu-ssion took place between Cieoffroy Saint-Hilaire and Cuvicr. .\s professor of vertebrate zoologj- Saint-Hilaire (1772- 1814) had long been the colleague of Lamarck. Saint- Hilaire held the mutability of species, but ascribetl the main influence in its evolution to the "monde ambi-

ant". Besides, in order to account for the disconti- nuity of species, he imagined that the environment coultl produce sudden changes in the specific charac- ters of the embrj'o (Philosophie anatomique, 1818). In 1830 G. Saint-Hilaire presented to the French Academy of Sciences his doctrine of the tmiversal unity of plan and composition in the animal kingdom. Cuvier opposed it with his celebrated theory of the four "embranchements", and showed that his adver- sary had mistaken resemblance for imity. Cuvier brought convincing facts in support of his attitude; .Saint-Hilaire did not. That settleti the issue. The theorj' of evolution was officially abandoned. Natu- ralists left speculation and retm-ned for a few decades to an almost exchisive study of positive facts. A single writer of some celebrity, Borj' de Saint-Vincent (1780-1846), took up Lamarck's doctrines, but not without modifying them by insisting upon the final coiLstancy of specific characters through heretlity. Isidore Saint^HUaire (1805-61), who shared the views of his father concerning environment antl heredity, defendeti a verj- motierate theorj' of evolution. He assimied a limited variabilitj' of species according to the variability of the environment.

Second Period. — Charles Robert Darwin's book, on the " Origin of Species bj' means of natm-al selection or the preservation of fa-vouretl races in the struggle for life", published 24 November, 1859, marks a new epoch in the history of the evolution idea. Though the principal factors of Darwin's theory, namelj' "struggle, variation, selection "j had been emmciatetl by others, it was mainly Darwm who first combined them mto a sj'stem which he tried to support by an extensive empirical foundation. Assistetl by a num- ber of influential friends, he succeedeti in obtaining an almost universal acknowledgment for the general tlie- ory of evolution, though his special theorj- of natural selection gradually lost much of the significance at- tached to it, especiallj' by Darwin's extreme followers. Charles Robert Darwin was bom at Shrewsburj-, 12 Februarj', 1809. From 1831-36 he accompanied as naturalist an English scientific expedition to South America. In 1842 he retiretl to his villa at Down in Kent, w-here he wrote his niunerous works. He died on 19 April, 1882, and was buried in Westminster Abbej' a few feet from the grave of Newton. Bio- geographical observations on his voj'age to South America led Darwin to abandon the theory of special creation. " I had been deeplj' impressed ' ', he saj-s in his .\utobiographj', "bj' discovering in the Pampean formation great fossil animals covered with armoiu- like that on the existing armadillos; secondly bj- the manner in which closely allied animals replace one an- other in proceeding southward over the continent; antl thirdlj' bj' the South .American character of most of the productions of the Galapagos archipelago and more especially by the manner in which they differ slightly on each island of the group. ... It w-as evi- dent that such facts coultl onlj' be explained on the supposition that species graduallj- became modificil." In order to account for the transformation, Darwin began with a sj-steniatic studj- of nimierous facts re- ferring to domesticated animals and cultivated plants. This was in Julj-, 1837. He soon perceived that selec- tion was the kej-stone of man's success in making useful races, namelj-, bj' breetling onlj- from useful vari- ations. But it remained a mj-sterj- to him how- selec- tions could be applied to organisms living in nature. In October, 1838, Darwin read Malthus's "Essaj'on Population " and understood at once that in the strug- gle for existence described bj' Malthus "favourable variations would fend to be preserveti and unfa\-our- able ones to be destroj-eti. antl that the result of this selection or survival woultl be the formation of new species". The struggle itself appeared to him as a necessary consetiuence of the high rate at which or- ganic beings tend to increase. The result of the selec-