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Página 159 - In looking at Nature, it is most necessary to keep the foregoing considerations always in mind — never to forget that every single organic being around us may be said to be striving to the utmost to increase in numbers ; that each lives by a struggle at some period of its life ; that heavy destruction inevitably falls either on the young or old, during each generation or at recurrent intervals. Lighten any check, mitigate the destruction ever so little, and the number of the species will almost...
Página 170 - Owing to this struggle for life, any variation, however slight, and from whatever cause proceeding, if it be in any degree profitable to an individual of any species, in its infinitely complex relations to other organic beings and to its physical conditions of life, will tend to the preservation of that individual, and will generally be inherited by its offspring.
Página 159 - The face of Nature may be compared to a yielding surface, with ten thousand sharp wedges packed close together and driven inwards by incessant blows, sometimes one wedge being struck, and then another with greater force.
Página 170 - The offspring, also, will thus have a better chance of surviving, for, of the many individuals of any species which are periodically born, but a small number can survive. I have called this principle, by which each slight variation, if useful, is preserved, by the term of Natural Selection, in order to mark its relation to man's power of selection.
Página 168 - If selection consisted merely in separating some very distinct variety, and breeding from it, the principle would be so obvious as hardly to be worth notice ; but its importance consists in the great effect produced by the accumulation in one direction, during successive generations, of differences absolutely inappreciable by an uneducated eye — differences which I for one have vainly attempted to appreciate.
Página 221 - ... to be struck by other bodies in the same movement." This is a somewhat vague hypothesis, not supported by experiment or observation ; but whatever its value may be as regards them, the more artificial forms already found, however few in comparison, are amply sufficient to destroy the value of the doubt as affecting the general question. With regard to the more highly finished of those described by Mr. Evans, they show a uniformity of shape, a correctness of outline, and a sharpness about the...
Página 272 - So extensive are the ironstone beds of the coal measures, that they furnish in themselves the greater part of the iron produced in Great Britain; but the iron-making resources of the kingdom are by no means confined to them. The carboniferous, or mountain limestones of Lancashire, Cumberland, Durham, the Forest of Dean, Derbyshire, Somersetshire, and South Wales, all furnish important beds and veins of haematite ; those of Ulverston, Whitehaven, and the Forest of Dean are the most extensively worked,...
Página 140 - Another account in the same volume, by Pietro Jacobeo di Toledo, describing the same fact, adds, — " Some of the stones were larger than an ox. They were thrown up, the larger ones, about a cross-bow's shot in height from the opening, and then fell down, some on the edge of the mouth, some back into it. The mud ejected (ashes mixed with water) was at first very liquid, then less so, and in such quantities that, with the help of the aforementioned stones, a mountain was raised a thousand paces in...