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according acquired action adapted advantage amount animals appear beak become bees believe birds breeds called cause cells chapter characters climate closely colour common considered continued crossed descendants developed difficulty distinct domestic doubt effects eggs existence extinct extremely facts favourable flowers forms genera genus give given greater groups habits hand Hence highly important improved increase individuals inhabitants inherited insects instance instincts intermediate kind known laws less living look males manner marked means modified namely natural selection naturalists nearly nest never object observed occasionally occur organs origin parent perfect period pigeons plants points present preserved principle probably produced races rank rarely reason relation remarked resemble respect seeds seems seen shown side similar slight sometimes species structure struggle supposed tend tion tree variability variations varieties vary whole widely young
Página 103 - It may be said that natural selection is daily and hourly scrutinising, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working, whenever and wherever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life.
Página 84 - The action of climate seems at first sight to be quite independent of the struggle for existence; but in so far as climate chiefly acts in reducing food, it brings on the most severe struggle between the individuals, whether of the same or of distinct species, which subsist on the same kind of food.
Página 203 - Our ignorance of the laws of variation is profound. Not in one case out of a hundred can we pretend to assign any reason why this or that part differs, more or less, from the same part in the parents.
Página 321 - 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.
Página xx - The Archetypal idea was manifested in the flesh, under divers modifications, upon this planet, long prior to the existence of those animal species that actually exemplify it.
Página 35 - It would seem as if they had chalked out upon a wall a form perfect in itself, and then had given it existence." In Saxony the importance of the principle of selection in regard to merino sheep is so fully recognised, that men follow it as a trade: the sheep are placed on a table and are studied, like a picture by a connoisseur; this is done three times at intervals of months, and the sheep are each time marked and classed, so that the very best may ultimately be selected for breeding.
Página 110 - Let us take the case of a wolf, which preys on various animals, securing some by craft, some by strength, and some by fleetness; and let us suppose that the fleetest prey, a deer for instance, had from any change in the country increased in numbers, or that other prey had decreased in numbers, during that season of the year when the wolf was hardest pressed for food. Under such circumstances the swiftest and slimmest wolves would have the best chance of surviving...
Página 88 - ... plantations, which were not to be seen on the heath ; and the heath was frequented by two or three distinct insectivorous birds. Here we see how potent has been the effect of the introduction of a single tree...
Página 162 - The limbs divided into great branches, and these into lesser and lesser branches, were themselves once, when the tree was small, budding twigs; and this connection of the former and present buds by ramifying branches may well represent the classification of all extinct and living species in groups subordinate to groups.