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Chapter IV of "the origin of species" Natural Selection -- its power compared with man's selection -- its power on characters of trifling importance -- its power at all ages and on both sexes -- Sexual Selection -- On the generality of intercrosses between individuals of the same species -- Circumstances favourable and unfavourable to the results of Natural Selection, namely, intercrossing, isolation, number of individuals -- Slow action -- Extinction caused by Natural Selection -- Divergence of Character, related to the diversity of inhabitants of any small area and to naturalisation -- Action of Natural Selection, through Divergence of Character and Extinction, on the descendants from a common parent -- Explains the Grouping of all organic beings -- Advance in organisation -- Low forms preserved -- Convergence of character -- Indefinite multiplication of species -- Summary of chapter.
Published: Mon, 13 Apr 2020 14:55:23 GMT
La théorie de la sélection naturelle telle qu'elle a été initialement décrite par Charles Darwin, repose sur trois principes : le principe de variation, le principe d'adaptation, et le principe d'hérédité.
Published: Tue, 07 Apr 2020 12:59:14 GMT
Inasmuch as peculiarities often appear under domestication in one sex and become hereditarily attached to that sex, so no doubt it will be under nature. Thus it is rendered possible for the two sexes to be modified through natural selection in relation to different habits of life, as is sometimes the case; or for one sex to be modified in relation to the other sex, as commonly occurs. This leads me to say a few words on what I have called sexual selection. This form of selection depends, not on a struggle for existence in relation to other organic beings or to external conditions, but on a struggle between the individuals of one sex, generally the males, for the possession of the other sex. The result is not death to the unsuccessful competitor, but few or no offspring. Sexual selection is, therefore, less rigorous than natural selection. Generally, the most vigorous males, those which are best fitted for their places in nature, will leave most progeny. But in many cases victory depends not so much on general vigour, but on having special weapons, confined to the male sex.
Published: Tue, 07 Apr 2020 12:24:03 GMT
Extract of the Introduction
THE NATURE of the following work will be best understood by a brief account of how it came to be written. During many years I collected notes on the origin or descent of man, without any intention of publishing on the subject, but rather with the determination not to publish, as I thought that I should thus only add to the prejudices against my views. It seemed to me sufficient to indicate, in the first edition of my Origin of Species, that by this work "light would be thrown on the origin of man and his history"; and this implies that man must be included with other organic beings in any general conclusion respecting his manner of appearance on this earth. Now the case wears a wholly different aspect. When a naturalist like Carl Vogt ventures to say in his address as President of the National Institution of Geneva (1869), "personne, en Europe au moins, n'ose plus soutenir la creation independante et de toutes pieces, des especes," it is manifest that at least a large number of naturalists must admit that species are the modified descendants of other species; and this especially holds good with the younger and rising naturalists.
Published: Sun, 01 Mar 2020 15:56:20 GMT
Extact of the INTRODUCTION.
When on board H.M.S. Beagle, as naturalist, I was much struck with certain facts in the distribution of the organic beings inhabiting South America, and in the geological relations of the present to the past inhabitants of that continent. These facts, as will be seen in the latter chapters of this volume, seemed to throw some light on the origin of species--that mystery of mysteries, as it has been called by one of our greatest philosophers. On my return home, it occurred to me, in 1837, that something might perhaps be made out on this question by patiently accumulating and reflecting on all sorts of facts which could possibly have any bearing on it. After five years' work I allowed myself to speculate on the subject, and drew up some short notes; these I enlarged in 1844 into a sketch of the conclusions, which then seemed to me probable: from that period to the present day I have steadily pursued the same object. I hope that I may be excused for entering on these personal details, as I give them to show that I have not been hasty in coming to a decision.
Published: Sun, 01 Mar 2020 15:53:32 GMT
extract of the Preface :
I have stated in the preface to the first Edition of this work, and in the Zoology of the Voyage of the Beagle, that it was in consequence of a wish expressed by Captain Fitz Roy, of having some scientific person on board, accompanied by an offer from him of giving up part of his own accommodations, that I volunteered my services, which received, through the kindness of the hydrographer, Captain Beaufort, the sanction of the Lords of the Admiralty. As I feel that the opportunities which I enjoyed of studying the Natural History of the different countries we visited, have been wholly due to Captain Fitz Roy, I hope I may here be permitted to repeat my expression of gratitude to him; and to add that, during the five years we were together, I received from him the most cordial friendship and steady assistance. Both to Captain Fitz Roy and to all the Officers of the Beagle  I shall ever feel most thankful for the undeviating kindness with which I was treated during our long voyage.
Published: Sun, 01 Mar 2020 15:50:12 GMT
Les Mardis de l'Espace des sciences avec Pierre-Henri Gouyon, Directeur du Laboratoire Ecologie
Published: Fri, 03 Jun 2016 16:26:29 GMT
Why can't women just get pregnant without the menstrual cycle?
Published: Fri, 04 Apr 2014 12:13:36 GMT
Advanced forms of life existed on earth at least 3.5 billion years ago, ie. 1 billion years after the earth was formed.
In rocks of that age, fossilized imprints have been found of bacteria that look uncannily like cyanobacteria, the most highly evolved photosynthetic organisms present in the world today. Carbon deposits enriched in the lighter carbon12 isotope over the heavier carbon13 isotope, a sign of biological carbon assimilation, attest to an even older age. On the other hand, it is believed that our young planet, still in the throes of volcanic eruptions and battered by falling comets and asteroids, remained inhospitable to life for about half a billion years after its birth together with the rest of the solar system, some 4.5 billion years ago. This leaves a window of perhaps 200-300 million years for the appearance of life on earth.
Published: Wed, 02 Apr 2014 17:54:37 GMT
Voici une spéculation sur les origines d'Homo.sapiens.sapiens. Elle est suggérée par le livre de Jared Diamond "le troisième chimpanzé" c'est à dire nous les hommes modernes, Homo.sapiens.sapiens, qui sommes caractérisés par la propension à nous entre tuer, et qui sommes dotés, après 35 000 ans d'évolution culturelle et technique, des moyens techniques formidables de détruire l'environnement dont nous dépendons et la planète toute entière.
Published: Wed, 02 Apr 2014 17:51:37 GMT
Pascal Picq (né le 22 janvier 1954 à Bois-Colombes en France) est un paléoanthropologue français, maître de conférences au Collège de France où il collabore avec le professeur Yves Coppens. Il est l'auteur de plusieurs ouvrages et articles scientifiques autour de la question de « Qu'est-ce que l'humain ? ». Il cherche surtout à trouver ce qu'est le propre de l'espèce humaine : « Le propre de l'humain n'est-il pas justement de se poser cette question : « Qu'est ce que l'humain ? » Et est-ce ce sens propre à notre espèce Homo sapiens ? Dans ce cas, les autres hommes, dits préhistoriques, étaient-ils des humains1 ? »
Published: Wed, 02 Apr 2014 16:16:20 GMT
Nos origines sont africaines, mais il a fallu attendre 1959, soit exactement un siècle après la publication de « l’Origine des espèces au moyen de la sélection naturelle », pour qu’on vérifie l’hypothèse avancée par Charles Darwin dans « La filiation de l’Homme en relation avec la sélection sexuelle » de 1871. Comment a-t-il élaboré cette hypothèse ? Tout simplement en se fondant sur les relations de parenté entre l’Homme et les grands singes africains – les gorilles et les chimpanzés -. Les nombreux fossiles découverts depuis – Mr. Zinj, Ms. Ples, Lucy, Abel, Nariokotome Boy, Toumaï, Ida et tant d’autres – sortent des sédiments grâce à la plus grande théorie jamais forgée par le génie humain : l’évolution.
Published: Wed, 02 Apr 2014 16:04:12 GMT
Published: Thu, 19 May 2011 08:30:25 GMT
nous donne une biographie complète de Darwin et nous fait comprendre la continuité entre la sélection naturelle comme sélection des plus aptes, et l'évolution sociale vers la civilisation par laquelle l'homme échappe au processus de la sélection naturelle par ses capacités cognitives.
Published: Fri, 11 Mar 2011 09:59:14 GMT
Published: Thu, 10 Mar 2011 02:34:32 GMT