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last a generation will appear which differs markedly from the original form. Let us suppose that a good many plants of the same kind are growing together in a very dry place. As the hairs on the leaves are very useful for drawing moisture from the air, it follows that in this unfavourable place where the plants are suffering from the want of water, and are struggling with each other to obtain water, the individuals with the hairiest leaves will be the most favoured. These only will survive, while the others with smoother leaves will die. The hairier kinds will reproduce themselves, and their descendants will be even more remarkable for having leaves with thick strong hairs than were the plants of the first generation. If this process is continued through many generations in the same place, this peculiarity will at length be so much increased, the number of hairs on the surface of the leaves will be so much greater, that the plant will appear to be a new species. And besides this, it must be remembered that all the parts of an organism are connected together, and that therefore, as a rule, no part can be altered without its affecting other parts also. For instance, if the number of hairs on the leaves of a plant increases, nourishment will probably be withdrawn from other parts of the plant ; the material which might go towards forming blossoms or seeds is diminished, the blossoms or seeds become smaller, and this will be the mediate or indirect result of the struggle for existence, which at first only produced a change in the leaves.
I add an example quoted by Darwin from the animal world. Wolves obtain their prey partly by craft, partly by strength, partly by fleetness. Let us suppose that the fleetest prey-a deer for instance—had increased in number in a certain region, or that other prey had decreased during that season of the year when the wolf is hardest pressed for food. Under these circumstances those wolves are the most likely to obtain nourishment who are most qualified to hunt down the swift-footed stags, that is, those wolves who are swiftest and slimmest. These will remain alive, and will reproduce themselves, while the short-legged, heavy wolves will die out under the given conditions. So that in this case a slim, swift variety of wolf will be produced, and other structural alterations will occur owing to the influence of the separate parts of the organism on one another, which I have alluded to above.
In describing this struggle for existence, and the natural selection which it brings about, Darwin also notices the fact which, as I mentioned above, was first discovered by Lamarck, namely, that the organs are strengthened and perfected by use, and stunted by disuse. For instance, in consequence of the increase of insect-eating mammals in a certain region, the food of the latter becomes scanty. Only ants or termites are left in any quantity. Some of the insect-eaters who are thus forced to feed on ants become accustomed to it and suffer no want, while the others who cannot accustom themselves to this food die out. Ant-eating specially develops certain muscles of the tongue. The mouth need not be opened widely for it, and it therefore remains small. In the course of several thousand generations the whole organization of the animal accommodates itself more and more to the new way of life, and thus an animal is formed which is, as it were, made for ant-eating. Ant-eating has therefore produced the peculiar shape of the ant-eater. Or a bird of prey accustoms itself to seeking its prey by night, because it gets more booty by surprising animals in their sleep, or by catching night animals. In him and his descendants the eye accustoms itself to the darkness, and becomes keener by continual usage, and thus the owl's eyes are produced. On the other hand, just as the owl's eye becomes keener in darkness, the mole becomes blind, because he tracks his prey by smell. And in subterranean caves we find animals who have only stunted rudimentary eyes. As the eye was not used, it no longer attained to its normal development, and in later generations it became more and more stunted. According to this supposition the blind or short-sighted animals found in dark caves might be descended from animals like themselves in all but sight. The difference between them came about in the course of ages through the struggle for existence, and the gradual harmonizing of the organism to the conditions of life.
Darwin admits in his latter work that he ascribed too much to natural selection. He now seeks to find a new support for his theory by taking sexual selection to aid natural selection. Sexual selection, he says, depends on the advantage which certain individuals possess over other individuals of the same species exclusively with regard to reproduction. Males who have better organs of sense, and locomotive and prehensile organs, better means of attack and defence than their rival males, and males who are more attractive to the females by reason of their form, the colour of their plumage, their song, etc., pair more easily than do the
less well-furnished males, and transmit the advantages they possess to their descendants.
For instance, it is well known that in the rutting season the male stag fights for the possession of the does. The principal weapons in these fights are the horns. Therefore those stags will always remain victorious, and will attain to reproduction, whose horns are best fitted for fighting, while those less well provided will not be able to pair. The individual advantage possessed by. the stags who are able to pair will be inherited by their offspring, and will probably be increased in each generation according to the rule which I mentioned when speaking of artificial selection. If, therefore, we go back in the history of stags, we may assume that the present shape of the horns has been formed by degrees; that the ancestors of the present stags many thousand years ago had only quite small horns, and therefore in this matter were not different from roes and goats; and that the present difference is the work of time and continued sexual selection. The mane is an important weapon of protection to the lion, as it preserves him from wounds on the head and neck while fighting with rivals. The lion who has the thickest mane is therefore in a position of advantage while fighting for the female, and therefore the formation of the lion's mane, like that of the stag's horns, may be a result of sexual selection.
In these cases the combat lies between individuals of the male sex; they seek to kill or drive away their rivals, while the females remain passive. In other cases the struggle takes place in a different way, the males vieing with one another to excite or charm the female,
Just published, in Two Vols., extra 8vo (about 1400 pp.), price 258.,
WILLIAM G. T. SHEDD, D.D.,
PROFESSOR OF SYSTEMATIC THEOLOGY IN UNION THEOLOGICAL SEMINARY,
NEW YORK; AUTHOR OF 'A HISTORY OF CHRISTIAN DOCTRINE,' 'SERMONS TO THE NATURAL MAN,'
SERMONS TO THE SPIRITUAL MAN,' ETC. ETC.
THEOLOGICAL INTRODUCTION. CHAP. I.—The True Method in Theological Science. II.- Plan, Divisions, and
Subdivisions. III.-Nature and Definition of Theological Science.
BIBLIOLOGY. Chap. I. -Revelation and Inspiration. II.-Authenticity of the Scriptures. III.
Credibility of the Scriptures. IV.-Canonicity of the Scriptures.
THEOLOGY (DOCTRINE OF GOD).
Arguments for the Divine Existence. IV.- Trinity in Unity. V.-Divine
IV.-Man's Probation and Apostasy. V.-Original Sin.
CHRISTOLOGY. CHAP. I.-Christ's Theanthropic Person. II.-Christ's Divinity. III.—Christ's
Humanity. IV.-Christ's Unipersonality. V.-Christ's Impeccability.
SOTERIOLOGY. CHAP. 1.-Christ's Mediatorial Offices. II.- Vicarious Atonement. III.-Re
generation. IV.-Conversion. V.- Justification. VI.-Sanctification. VII.-The Means of Grace.
ESCHATOLOGY. CHAP. I.-The Intermediate or Disembodied State. II.-Christ's Second Advent.
III.-The Resurrection. IV.- The Final Judgment. V.--Heaven. VI.
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