Page:Encyclopædia Britannica, Ninth Edition, v. 8.djvu/787

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EVOLUTION

apply to species, it would not only SOlVC the problem of their evolution, but that it would account for the facts of teleology, as well as for those of morpholog ; aml for the persistence of some forms of life unchanged through long epochs of time, while others undergo comparatively rapid metamorphosis.

How far “ natural selection ” suffices for the production of species remains to be seen. Few can doubt that, if not the whole cause, it is a very important factor in that operation ; and that it nmst play a great part in the Sorting out of varieties into those which are transitory and those which are permanent.

But the causes and conditions of variation have yet to be thoroughly explored ; and the importance of natural selec- tion will not be impaired, even if further inquiries should prove that variability is definite, and is determined in certain directions rather than in others, by conditions inherent in that which varies. It is quite conceivable that every species tends to produce varieties of a limited number and kind, and that the effect of natural selection is to favour the develop- ment of some of these, while it opposes the development of others along their predetermined lines of modiﬁcation.

7. N o truths brought to light by biological investigation were better calculated to inspire distrust of the dogmas intruded upon science in the name of theolog, than those which relate to the distribution of animals and plants on the surface of the earth. Very skilful accommodation was ueedful, if the limitation of sloths to South America, and of the ornithorhynchus to Australia, was to be reconciled with the literal interpretation of the history of the deluge; and, with the establishment of the existence of distinct provinces of distribution, any serious belief in the peopling of the world by migration from Mount Ararat came to an end.

Under these circumstances, only one alternative was left for those who denied the occurrence of evolution ; namely, the supposition that the characteristic animals and plants of each great province were created, as such, within the limits in which we ﬁnd them. And as the hypothesis of “speciﬁc centres,” thus formulated, was heterodox from the theological point of view, and unintelligible under its scientific aspect, it may be passed over without further notice, as a phase of transition from the creational to the evolutional hypothesis.

8. In fact, the strongest and most conclusive arguments in favour of evolution are those which are based upon the facts of geographical, taken in conjunction with those of geological, distribution.

Both Mr Darwin and Mr \Vallace lay great stress on the close relation which obtains between the existing fauna of any region and that of the immediately antecedent geological epoch in the same region; and rightly, for it is in truth inconceivable that there should be no genetic connection between the two. It is possible to put into words the proposition, that all the animals and plants of each geological epoch were annihilated, and that a new set of very similar forms was created for the next epoch, but it may be doubted if any one who ever tried to form a (listiIICt mental image of this process of spontaneous generation on the grandest scale, ever really succeeded in realizing it.

Within the last twenty years, the attention of the best pala‘ontologists has been withdrawn from the hodman’s work of making “ new species” of fossils, to the scientiﬁc

' task of completing our knowledge of individual species, and

tracing out the succession of the forms presented by any giVen type in time.

Those who desire to inform themselves of the nature and extent of the evidence bearing on these questions may

consult the works of Iliitimeyer, Gaudry, liowalewsky,l

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Marsh, and the writer of the present article. It must suffice, in this place, to say that the successive forms of the Equine type have been fully worked out ; while those of nearly all the other existing types of Ungulate mammals and of the Carnivora have been nearly as closely followed through the Tertiary deposits ; the gradations between birds and reptiles have been traced ; and the modiﬁcations undergone by the Crocodilia, from the Triassic epoch to the present day, have been demonstrated. On the evidence of palaeontology, the evolution of many existing forms of animal life from their predecessors is no longer an hypo- thesis, but an historical fact ; it is only the nature of the physiological factors to which that evolution is due which is still open to discussion. ('1‘. H. H.)

II. EVOLUTION IN PHILOSUPHY.

Deﬁnition—The modern biological doctrine of evolu- tion, which regards the higher forms of life as gradually arising out of the lower, owes its chief philosophic signi- ﬁcance to the fact that it renders deﬁnite and precise one part of a general theory of the world viewed as an orderly succession of events or as a process of be- coming. This theory is put forward as an answer to one of the two problems of philosophy conceived as an interpretation of real existence. The ﬁrst of these pro- blems concerns itself with what may be called the stati- cal 'aspect of the world, and inquires into the ultimate nature of all reality (matter and mind), viewed as coexistent and apart from time. The second problem treats of the dynamical aspect of the World, and has to do with the pro- cess by which the totality of things has come to be what it is, and is still being transformed. It is this latter problem which the various theories of evolution seek to solve.

The most general meaning of evolution may be deﬁned as follows: Evolution includes all theories respecting the origin and order of the world which regard the higher or more complex forms of existence as following and depend- ing on the lower and simple forms, which represent the course of the world as a gradual transition from the inde- terminate to the determinate, from the uniform to the varied, and which assume the cause of this process to be immanent in the world itself that is thus transformed. All theories of evolution, properly so called, regard the physical world as a gradual progress from the simple to the complex, look upon the development of organic life as conditioned by that of the inorganic world, and view the course of mental life both of the individual and of the race as correlated with a material process. This deﬁnition covers roughly the principal historical systems bearing the name of evolution, as well as others which have hardly as yet been characterized by this title.

It is clear by this definition that we cannot now press the etymological force of the word. Evolution has no doubt often been conceived as an unfolding of something already contained in the original, and this view is still com- monly applied to organic evolution both of the individual and.of the species. It will be found that certain metaphy- sical systems of evolution imply this idea of an unfolding of something existing in germ or at least potentially _1n the antecedent. On the other hand, the modern doctriue of evolution, with its ideas of elements which combine, and -of causation as transformation of energy, does not necessarily imply this notion. It may be remarked that some of the arguments brought against the modern doctrine rest .on the fallacious assumption that the word is still used in 1ts ety— mological sense, and that consequently that which eVolves must contain in some shape what is evolved (0.0., Inorganic matter must contain life and consciousness).

Evolution is thus almost synonymous with progress,