Comentarios de la gente - Escribir un comentario
Otras ediciones - Ver todas
action adapted advantage allied America amount ancient animals appear become believe birds breeds called cause chapter characters climate closely common compared considered continuous crossed descended developed difficulty distinct domestic doubt effects existing extinct extremely facts families favourable fertility flowers follow formations forms genera genus geological give given greater groups habits hand Hence hybrids important improved increase individuals inhabitants inherited insects instance instincts intermediate islands kind known land laws less lines living look male manner means modification namely natural selection naturalists nearly never occur offspring organic origin parent perfect period plants points present principle probably produced range ranked reason remarked seeds seems seen separated single slight sometimes species sterility structure struggle successive suppose tend theory tion variability variation varieties vary whole widely
Página 424 - In the distant future I see open fields for far more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. Light will be thrown on the origin of man and his history.
Página 79 - I may be allowed to personify the natural preservation or survival of the fittest, cares nothing for appearances, except in so far as they are useful to any being. She can act on every internal organ, on every shade of constitutional difference, on the whole machinery of life. Man selects only for his own good: Nature only for that of the being which she tends.
Página 70 - I counted thirtytwo little trees ; and one of them, with twenty-six rings of growth, had during many years tried to raise its head above the stems of the heath, and had failed. No wonder that, as soon as the land was enclosed, it became thickly clothed with vigorously growing young firs. Yet the heath was so extremely barren and so extensive that no one would ever have imagined that cattle would have so closely and effectually searched it for food. Here we see that cattle absolutely determine the...
Página 169 - If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down.
Página 63 - Hence as more individuals are produced than can possibly survive, there must in every case be a struggle for existence, either one individual with another of the same species, or with the individuals of distinct species, or with the physical conditions of life.
Página 167 - To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree.
Página 378 - Nothing can be more hopeless than to attempt to explain this similarity of pattern in members of the same class, by utility or by the doctrine of final causes. The hopelessness of the attempt has been expressly admitted by Owen in his most interesting work on the 'Nature of Limbs.
Página 187 - Under changed conditions of life, it is at least possible that slight modifications of instinct might be profitable to a species; and if it can be shown that instincts do vary ever so little, then I can see no difficulty in natural selection preserving and continually accumulating variations of instinct to any extent that was profitable. It is thus, as I believe, that all the most complex and wonderful instincts have originated.