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 EVOLUTION

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EVOLUTION

fere directly with the natural ortler, where secondary causes suffice to produce the intended effect " (De opere sex dierum, II, c. x, n. 13). In the light of this prin- ciple of the Christian interpretation of nature, the his- tory of the animal and vegetable kingdoms on our planet is, as it were, a versicle in a volume of a million pages in which the natural development of the cosmos is described, and upon whose title-page is written: " In the beginning God created heaven and earth."

(2) The theory of evolution just stated rests on a theistic foundation. In contradistinction to this is another theory resting on a materialistic and atheistic basis, the first principle of which is the denial of a per- sonal Creator. This atheistic theory of evolution is ineffectual to account for the first beginning of the cosmos or for the law of its evolution, since it acknowl- edges neither creator nor lawgiver. Natural science, moreover, has proved that spontaneous generation — i. e. the independent genesis of a living being from non-living matter — contradicts the facts of observa- tion. For this reason the theistic theory of evolution postulates an intervention on the part of the Creator in the production of the first organisms. When and how the first seeds of life were implanted in matter, we, indeed, do not know. The Christian theory of evolution also demands a creative act for the origin of the human soul, since the soul cannot have its origin in matter. The atheistic theory of evolution, on the contrary, rejects the assumption of a soul separate from matter, and thereby sinks into blank materi- alism.

(3) Darwinism and the theory of evolution are by no means equivalent conceptions. The theory of evolu- tion was propounded before Charles Darwin's time, by Lamarck (1S09) and Geoffrey de Saint-Hilaire. Dar- win, in 1859, gave it a new form by endeavouring to explain the origin of species by means of natural selec- tion. According to this theory the breeding of new species depends on the sui-vival of the fittest in the struggle for existence. The Darwinian theory of se- lection is Darwinism — adhering to the narrower, and accurate, sense of the word. As a theory, it is scien- tifically inadequate, since it does not account for the origin of attributes fitted to the purpose, which must be referred back to the interior, original causes of evo- lution. Haeckel, with other materialists, has en- larged this selection theory of Darwin's into a philo- sophical world-idea, by attempting to account for the whole evolution of the cosmos by means of the chance survival of the fittest. This theory is Darwinism in the secondary, and wider, sense of the word. It is that atheistical form of the theory of evolution which was shomi above — under (2) — to be untenable. The third signification of the term Darwinism arose from the application of the theory of selection to man, which is likewise impossible of acceptance. In the fourth place, Darwinism frequently stands, in popular usage, for the theory of evolution in general. This use of the word rests on an evident confusion of ideas, and must therefore be set aside.

(4) To what extent is the theory of evolution appli- cable to man? — That God should have made use of natural, evolutionary, original causes in the produc- tion of man's body, is per se not improbable, and was propounded by St. Augustine (see Augu.stinb op Hippo, S.\int, under V. Aiiguslinism in History). The actual proofs of the descent of man's body from ani- mals is, however, inadequate, especially in respect to palaeontology. And the human soul could not have been derived through natural evolution from that of the brute, since it is of a spiritual nature; for which reason we must refer its origin to a creative act on the part of God.

For a thorough exposition, Wabmann, Modern Biology and Ihe Theory of Eitolulion (Freiburg im Br., 1904). Of the older literature, Mivart. On the Genesis of Species (London and New York, 1871).

E. Wasmann.

B. History and Scientific Foundations. — The world of organisms comprises a great system of in- dividual forms generally classified according to struc- tural resemblances into kingdoms, classes, orders, families, genera, species. The species is considered as the unit of the system. It is designated by a double name, the first of which indicates the genus, e. g. canis familiaris, the dog, and canis lupus, the wolf. Com- paring the species of the present day with their fossil representatives in the geological layers, we find that they differ from one another the more the farther we retrace the geological record. To explain this remark- able fact two theories have been proposed, the one maintaining the stability and special creation of species, the other the instability and evolution, or genetic relation, of species. As is plain from the preceding section of this article, the principal difference between the two theories consists in this: that the theory of evolution derives the species of to-day by a progressive development from one or more primitive types, whilst the theory of constancy insists upon the special creation of each true species. It is generally ad- mitted that the determination of specific forms de- pends largely on the subjective views and experience of the naturalist.

We shall here confine our attention to the history and scientific foundations of the biological theory of evolution, leaving all purely philosophical and theo- logical discussions to others. The entire subject will here be divided into the following parts: I. History OF THE Scientific Theories of Evolution; II. Definition of Species; III. Variability and Ex- periment.\l Facts Relating to the Evolution of Species; IV. The Pal.eontological Argument; V. The Morphological Argument; VI. The Onto- genetic Argu.ment; VII. The Biogeographical Argu.ment.

Before we begin, we wish to remind the reader of the important distinction brought out in the preceding essay, that the general theory referring to the mere fact of evolution must be well distinguished from all special theories which attempt to explain the assumed fact by ascribing it to certain causes, such as natural selection, the influence of environment, and the like. In other words, an evolutionist — that is, a defender of the general scientific theory of evolution — is not eo ipso a Darwinian, or a Lamarckian, or an adherent of any special evolutionary system. No less important are the other definitions and distinctions emphasized above under A.

I. History of the Scientific Theorie.9 of Evo- lution. — The historical development of the scientific theories of evolution may be divided into three peri- ods. The main figure of the first period is Lamarck. The period ends with an almost complete victory of the theory of constancy (1S30). The second period commences with Darwin's "Origin of Species" (1859). The idea of evolution, and in particular Darwin's the- ory of natural selection, enters into every department of the biological sciences and to a great extent trans- forms them. The third period is a time of critical reaction. Natural selection is generally considered as insufficient to explain the origin of new characters, while the ideas of Lamarck and G. Saint-Hilaire become prevalent. Besides, the theory of evolution is tested experimentally. Typical representatives of the period are Bateson, Hugo de Vries, Morgan.

First Period. — Linna;us based his important "Sys- tema naturie" on the principle of the constancy and special creation of every species — " Species tot numer- amus quot di versa: forma; in principio sunt creatse" (" Philosophia botanica", Stockholm, 1751, p. 99). For. "contemplating the works of God, it is plain to every one that organisms produce offspring perfectly similar to the parents" ("Systema", Leipzig, 1748, p. 21). Liniucus had a vast influence upon the nat- urahsts of his time. Thus his principle of the con-