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 EVOLUTION

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EVOLUTION

evolved into higher plants and animals, man included. As one of his main arguments, Haeckel refers to the so- called "biogenetic law of development". The sup- posed law maintams that ontogeny is a short and rapid repetition of phylogeny, that is, the stages in the individual development of an organism correspond more or less to the stages which the species passed through in their evolution. The causes of develop- ment are, according to Haeckel, the same as were proposed by Darwin and by Lamarck; but Haeckel denies the existence of God and rejects the idea of tele- ology.

Our leading scientists do not care to support the un- founded generalities of Haeckel 's doctrines. They have even, most severely, but justly, censured Haeck- eVs scientific methods, mainly his frauds, his want of distinction between fact and hypothesis, his neglect to correct wrong statements, his disregard of facts not agreeing with his aprioristic conceptions and his im- acquaintance with history, physics, and even modern biology. They have also pointed out that the bio- genetic law of development is by no means a trust- worthy guide in retracing the phylogenetic succession of species, and that many other theories suggested by Haeckel are without foundation. But above all we must reject Haeckel's popular writings because they contain numerouserrorsof every kind, and ridicule in a shameful manner the most sacred convictions and moral principles of Christianity. It is a sad fact, that especially through the influence of "Die Weltratsel" great harm was done to religion and morality, especially in Germany and in the English-speaking countries.

The present leader of extreme Darwinism is August Weismann of Freiburg (Vortrage tlber Descendenzthe- orie, 2d ed., 1904), the energetic opponent of Lamarck's idea that acquired characters are inherited. .Accord- ing to Weismann, every individual and specific char- acter which may be transmitted by heredity is pre- formed and prearranged in the architecture of certain ultra-microscopical particles composing the chromatin of the germ-cells. On account of qualitative differ- ences the various groups of these ultimate particles or "biophores" have a different power of assimilation. Besides, they are present in different numbers. In consequence thereof an intracellular struggle for exist- ence will arise, especially after the germ-cells are united in fertilization. The outcome of the struggle will be that the weaker particles always or at times succumb. Thus the principle of the survival of the fittest is transferred to the germ-cells. Weismann, moreover, admits an indirect influence of the environ- ment upon the germ-cells. In order to account for the facts of regeneration and reorganization established by Driesch, Morgan, and others, Weismann appeals at times to unknown forces of vital affinities, without, however, dismissing his thoroughly materialistic and antiteleological suppositions. It will be superfluous to add that WeLsmann's theory is a mere hypothesis whose foundation can probably never be controlled by obser\'ation and experiment. But it must be ac- knowledged that Weismann was among the first to point out the intrinsic connexion between the evolu- tion of species and the science of the cell. As extreme scientific opponents of Darwinism and evolution we mention above all the botanist Albert Wiegand and the zoologist and pala?ontologist Louis Agassiz, the well-known adversary of Asa Gray. These men pro- duced many an excellent argument against the ex- treme defenders of pure Darwinism, but, probably by attending too much to the exceedingly weak founda- tion.s of the current theory of the general development by small changes, they rejected evolution almost en- tirely. The most recent representative of such ex- treme views is the zoologist .\lbert Fleischmann, who has become a complete scientific agno.stic.

Third Period. — The third period in the history of the biological evolution theory has only in recent years

assumed the form which marks it as a new epoch. It8 path was prepared by the fact that two classes of nat- uralists had in course of time been drawing nearer to one another. On the one hand were those whose work was merely critical, by discriminating clearly between Darwinism and evolution, and on the other hand those who gave their undivided attention to the work of experimental investigation. Only in recent years have the two classes jomed hands and, in men like de Vries, Bateson, Morgan, have gained very effi- cient assistance. At the present time the greatest importance is laid on the explanation of the gaps in species, on the adaptation of organisms to environ- ment, and on the inheritance of characters thus ac- quired, and above all on the idea of the segregation and the independence of biological characters, as was pointed out almost fifty years ago by Gregor Johann Mendel.

.\s far back as 1865, K. von Nageli decided in favour of the general theory of evolution and against Darwin- ism. According to him progressive evolution required intrinsic laws of development, which, however, as he added, were to be sought for in molecular forces. Natural selection alone could only eliminate, that is to say, could only explain the survival of the more use- ful, but not its origin. Like Spencer, Nageli was a determined precursor of neo-Lamarckism. This the- ory, which is now defended by many evolutionists, attempts to reconcile Lamarck's principle of the use and disuse of organs with Saint-Hilaire's theory of the influence of external circumstances. There are many evolutionists, such as Th. Eimer, Packard, Cunning- ham, Cope, who defend this view. However, the experimental evidence for the foundation of neo-La- marckism — namely, the inheritance of acquired char- acters — is still wanting, or at least strongly debated. Nageli's most important work, " Mechanisch-physiol- ogische Theorie der .\bstammungslehre ", appeared in 1884. The embryologist K. E. von Baer, who did not share the antiteleological views of Nageli, opposed no less energetically Darwin's theorj- of natural selec- tion, because, as he argued, that theory does not ex- plain teleology and correlation, and is at the same time in contradiction to the persistence of species and varieties. He also vigorously controverted Haeckel's system, especially his biogenetic law of development. But he maintained the transformation of species within certain limits through the agency of grad- ual and sudden changes. This leads us to the theory of saltatory evolution which is to-day most strongly defended by Bateson, de Vries and others. Some of the first scientific expositors of this view were R. von KoUiker and St. George Mivart. In his work " On the Genesis of Species" (1871) Mivart proposed a number of convincing arguments against the opinion of the power of natural selection as a prevailing factor. Ac- cording to him species are suddenly born and originate by some innate force, which works orderly and with design. Mivart concedes that external conditions play an important part in stimulating, evoking, and in some way determining evolutionary processes. But the transformation of species will mainly, if not ex- clusively, be produced by some constitutional affec- tion of the generative system of the parental forms, an hypothesis which Mivart would extend also to the first genesis of the body o€ man. Hugo de Vries (Die Mutationstheorie, 1901-03) is, with Bateson, Reinke, and Morgan, a typical representative of the exponents of the modern theory of saltatory evolution. He first endeavoured to show experimentally that new species cannot arise by selection. Then he attempted to de- monstrate the origin of new forms by saltatory evolu- tion. The principal illustration to establish his theory of " mutation ' ' was the large flower, evening primrose ((Etwthera I.amarckiana) . Th. H. Morgan ("Evolu- tion and .adaptation", 1903) summarizes this view as follow. : "If we suppose that new mutations and