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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

common and widespread species which become the parents of new forms, and thus the non-variability of any number of rare or local species offers no difficulty whatever in the way of the theory of evolution. Concluding Remarks. We have now shown in some detail, at the risk of being tedious, that individual variability is a general character of all common and widespread species of animals or plants; and, further, that this variability extends, so far as we know, to every part and organ, whether

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

, and moths, among insects, all indicate an enormous amount of extinction among the comparatively low forms by which, on any theory of evolution, these higher and more specialised groups must have been preceded. Circumstances favourable to the Origin of New Species by Natural Selection. We have already seen that, when there is no change in the physical or organic conditions of a country, the effect of natural selection is to keep all the species inhabiting it in a state of perfect health and full

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

new species. This was the keynote of Mr. Vernon Wollaston's essay on Variation of Species, published in 1856, and it is adopted by the Rev. J. G. Gulick in his paper on Diversity of Evolution under one Set of External Conditions Journ. Linn. Soc. Zool., vol. xi. p. 496). The idea seems to be that there is an inherent tendency to variation in certain divergent lines, and that when one portion of a species is isolated, even though under identical conditions, that tendency sets up a divergence

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

another on the same side an equal distance apart. In a very lengthy paper, presented to the Linnean Society last year, on Divergent Evolution through Cumulative Segregation, Mr. Gulick endeavours to work out his views into a complete theory, the main point of which may perhaps be indicated by the following passage: No two portions of a species possess exactly the same average character, and the initial differences are for ever reacting on the environment and on each other in such a way as to

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

-eight different divisions and subdivisions, with an elaborate terminology, and he argues that these will frequently bring about divergent evolution without any change in the environment or any action of natural selection. The discussion of the problem here given will, I believe, sufficiently expose the fallacy of his contention; but his illustration of the varied and often recondite modes by which practical isolation may be brought about, may help to remove one of the popular difficulties in the

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

adjacent to the continental land of the period. The great thickness of some of the formations is no indication of a deep sea, but only of slow subsidence during the time that the deposition was in progress. This view is now adopted by many of the most experienced geologists, especially by Dr. Archibald Geikie, Director of the Geological Survey of Great Britain, who, in his lecture on Geographical Evolution, says: From all this evidence we may legitimately conclude that the present land of the globe

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

earth.1 Admitting, however, the extreme imperfection of the geological record as a whole, it may be urged that certain limited portions of it are fairly complete as, for example, the various Miocene deposits of India, Europe, and North America, and that in these we ought to find many examples of species and genera linked together by intermediate forms. It may be replied that in several cases this really occurs; and the reason why it does not occur more often is, that the theory of evolution requires

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

produces those puzzling discordances so generally met with in geological formations of marine origin. While a case of the kind now described affords evidence of the origin of species complete and conclusive, though on a necessarily very limited scale, the very rarity of the conditions which are essential to such completeness serves to explain why it is that in most cases the direct evidence of evolution is not to be obtained. [page] 38

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

to have migrated in early Miocene times, when a mild climate and luxuriant vegetation prevailed far within the arctic circle, it gave rise to the Ceratorhinus and the various horned rhinoceroses of late Tertiary times and of those now living. In America a 1 On Stagonolepis Robertsoni and on the Evolution of the Crocodilia, in Q. J. of Geological Society, 1875; and abstract in Nature, vol. xii. p. 38. [page] 38

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

of a good millstone. 1 We thus see that the Equid differ very widely in structure from most other mammals. Assuming the truth of the theory of evolution, we should expect to find traces among extinct animals of the steps by which this great modification has been effected; and we do really find traces of these steps, imperfectly among European fossils, but far more completely among those of America. It is a singular fact that, although no horse inhabited America when discovered by Europeans, yet

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

any kind of special creation, or by sudden advances of organisation in the offspring of preceding types, such close relationship would not be found; and facts of this kind become, therefore, to some extent a test of evolution under natural selection or some other law of gradual change. Of course the relationship will not appear when extensive migration has occurred, by which the inhabitants of one region have been able to take possession of another region, and destroy or drive out its original

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

the llama; besides many other extinct forms of intermediate types or of uncertain affinities.2 The extinct Moas of New Zealand huge wingless birds allied to the living Apteryx illustrate the same general law. The examples now quoted, besides illustrating and enforcing the general fact of evolution, throw some light on the usual character of the modification and progression of animal forms. In the cases where the geological record is tolerably complete, we find a continuous development of some

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

even a conifer (Cordaites Robbii) in the Upper Silurian; while the beds of graphite in the Laurentian were probably formed from terrestrial vegetation. On the whole, then, we may affirm that, although the geological record of the insect life of the earth is exceptionally imperfect, it yet decidedly supports the evolution hypothesis. The most specialised order, Lepidoptera, is the most recent, only dating back to the Oolite; the Hymenoptera, Diptera, and Homoptera go as far as the Lias; while

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

Cretaceous, when they gave way to the true osseous fishes, which had first appeared in the Jurassic period, and have continued to increase till the present day. This much later appearance of the higher osseous fishes is quite in accordance with evolution, although some of the very lowest forms, the lancelet and the lampreys, together with the archaic ceratodus, have survived to our time. The Amphibia, represented by the extinct labyrinthodons, appear first in the Carboniferous rocks, and these

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

Philosophy as any explanation of organic evolution, 1 an expression of opinion which would be repudiated by every Darwinian. For, even admitting the interpretation which Mr. Spencer puts on the facts he adduces, they are all included in the causes which Darwin himself recognised as having acted in bringing about the infinitude of forms in the organic world. In the concluding chapter of the Origin of Species he says: I have now recapitulated the facts and considerations which have thoroughly

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

of the successive evolution of physical conditions, may be regarded as the originator of the fittest, while natural selection is the tribunal to which all results of accelerated growth are submitted. This preserves or destroys them, and determines the new points of departure on which accelerated growth shall build. 1 This notion of intelligence the intelligence of the animal itself determining its own variation, is so evidently a very partial theory, inapplicable to the whole vegetable kingdom

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

in others it is widely removed, giving the idea, so consonant with the theory of evolution as developed by Darwin, that all are derived from a common ancestor, from which the existing anthropoid apes as well as man have diverged. When, however, we turn from the details of anatomy to peculiarities of external form and motions, we find that, in a variety of characters, all these apes resemble each other and differ from man, so that we may fairly say that, while they have diverged somewhat from

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

universe as a grand consistent whole adapted in all its parts to the development of spiritual beings capable of indefinite life and perfectibility. To us, the whole purpose, the only raison d' tre of the world with all its complexities of physical structure, with its grand geological progress, the slow evolution of the vegetable and animal kingdoms, and the ultimate appearance of man was the development of the human spirit in association with the human body. From the fact that the spirit of man the

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

recognition, 226 warning colours of, 233 sexual coloration of, 269 importance of dull colours to female, 272 visiting one kind of flower at a time, 318 and flowers, the most brilliant not found together, 335 Insects, no proof of love of colour by, 336 and birds at sea, 357 in mid-ocean, 359 at great altitudes, 360 geological distribution of, 403 ancestral in Silurian, 405 fossil support evolution, 405 Instability of useless characters, 138 Instinct, the theory of, 441 Insular organisms illustrate

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A1015 Book: Wallace, A. R. 1889. Darwinism: an exposition of the theory of natural selection with some of its applications. London & New York: Macmillan & Co. Text

, 155 Recognition marks of herbivora, 218 of birds, 222 of tropical forest birds, 224 of insects, 226 Reproductive functions, susceptibility of, 153 Reptiles, geological distribution of, 406 Rhinoceroses, evidence of evolution afforded by fossil, 383 Rocks, all stratified formed in shallow water, 344 Rocky Mountains, scarcity of monocotyledons in, 401 Rodents, prevent woody vegetation in the pampas, 23 Romanes, Professor G. J., on useless characters, 131, 139 on meaningless peculiarities of