Outlines of Evolutionary Biology

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D. Appleton, 1912 - 454 páginas
 

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Página 223 - From these remarks it will be seen that I look at the term species, as one arbitrarily given for the sake of convenience to a set of individuals closely resembling each other, and that it does not essentially differ from the term variety, which is given to less distinct and more fluctuating forms.
Página 392 - But as my conclusions have lately been much misrepresented, and it has been stated that I attribute the modification of species exclusively to natural selection, I may be permitted to remark that in the first edition of this work, and subsequently, I placed in a most conspicuous position — namely, at the close of the Introduction — the following words : " I am convinced that natural selection has been the main but not the exclusive means of modification.
Página 392 - This has been effected chiefly through the natural selection of numerous successive, slight, favorable variations ; aided in an important manner by the inherited effects of the use and disuse of parts; and in an unimportant manner, that is, in relation to adaptive structures, whether past or present, by the direct action of external conditions, and by variations which seem to us in our ignorance...
Página 390 - It would be in all respects better adapted to secure its safety, and to prolong its individual existence and that of the race. Such a variety could not return to the original form; for that form is an inferior one, and could never compete with it for existence. Granted, therefore, a 'tendency...
Página 383 - The whole train of animated beings, from the simplest and oldest up to the highest and most recent, are, then, to be regarded as a series of advances of the principle of development, which have depended upon external physical circumstances, to which the resulting animals are appropriate.
Página 393 - The hypothesis of Lamarck — that progressive changes in species have been produced by the attempts of animals to increase the development of their own organs, and thus modify their structure and habits — has been repeatedly and easily refuted by all writers on the subject of varieties and species...
Página 389 - It is, as we commenced by remarking, "a struggle for existence," in which the weakest and least perfectly organized must always succumb. Now it is clear that what takes place among the individuals of a species must also occur among the several allied species of a group — viz. that those which are best adapted to obtain a regular supply of food, and to defend themselves against the attacks of their enemies and the vicissitudes of the seasons, must necessarily obtain and preserve a superiority in...
Página 387 - The same spot will support more life if occupied by very diverse forms. We see this in the many generic forms in a square yard of turf...
Página 164 - The child, strictly speaking, does not grow into the man, but includes germs which slowly and successively become developed and form the man.
Página 373 - ... himself, as he is not naturally a carnivorous animal. So the horns of the stag are sharp to offend his adversary, but are branched for the purpose of parrying or receiving the thrusts of horns similar to his own, and have, therefore, been formed for the purpose of combating other stags for the exclusive possession of the females; who are observed, like the ladies in the time of chivalry, to attend the car of the victor.

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