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El contenido de este p\u00e1rrafo pertenece enteramente al cap\u00edtulo primero. Nada semejante a lo que ocurre en una granja tiene lugar en la naturaleza. Adem\u00e1s, en las granjas no se producen nuevas especies.<\/p>\n
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160.<\/em><\/p>\n As has always been my practice, I have sought light on this head from our domestic productions. We shall here find something analogous. It will be admitted that the production of races so different as short-horn and Hereford cattle, race and cart horses, the several breeds of pigeons, etc., could never have been effected by the mere chance accumulation of similar variations during many successive generations. In practice, a fancier is, for instance, struck by a pigeon having a slightly shorter beak; another fancier is struck by a pigeon having a rather longer beak; and on the acknowledged principle that \u00abfanciers do not and will not admire a medium standard, but like extremes,\u00bb they both go on (as has actually occurred with the sub-breeds of the tumbler-pigeon) choosing and breeding from birds with longer and longer beaks, or with shorter and shorter beaks. Again, we may suppose that at an early period of history, the men of one nation or district required swifter horses, while those of another required stronger and bulkier horses. The early differences would be very slight; but, in the course of time, from the continued selection of swifter horses in the one case, and of stronger ones in the other, the differences would become greater, and would be noted as forming two sub-breeds. Ultimately after the lapse of centuries, these sub-breeds would become converted into two well-established and distinct breeds. As the differences became greater, the inferior animals with intermediate characters, being neither very swift nor very strong, would not have been used for breeding, and will thus have tended to disappear. Here, then, we see in man’s productions the action of what may be called the principle of divergence, causing differences, at first barely appreciable, steadily to increase, and the breeds to diverge in character, both from each other and from their common parent.<\/em><\/p>\n \u00a0<\/em><\/p>\n Siguiendo mi costumbre, he buscado alguna luz sobre este particular en las producciones dom\u00e9sticas. Encontraremos en ellas algo an\u00e1logo. Se admitir\u00e1 que la producci\u00f3n de razas tan diferentes como el ganado vacuno short-horn y el de Hereford, los caballos de carrera y de tiro, las diferentes razas de palomas, etc., no pudo efectuarse en modo alguno por la simple acumulaci\u00f3n casual de variaciones semejantes durante muchas generaciones sucesivas. En la pr\u00e1ctica llama la atenci\u00f3n de un cultivador una paloma con el pico ligeramente m\u00e1s corto; a otro criador llama la atenci\u00f3n una paloma con el pico un poco m\u00e1s largo, y -seg\u00fan el principio conocido de que \u00ablos criadores no admiran ni admirar\u00e1n un tipo medio, sino que les gustan los extremos\u00bb- ambos continuar\u00e1n, como positivamente ha ocurrido con las sub-razas de la paloma volteadora, escogiendo y sacando cr\u00edas de los individuos con pico cada vez m\u00e1s largo y con pico cada vez m\u00e1s corto. M\u00e1s a\u00fan: podemos suponer que, en un per\u00edodo remoto de la historia, los hombres de una naci\u00f3n o pa\u00eds necesitaron los caballos m\u00e1s veloces, mientras que los de otro necesitaron caballos m\u00e1s fuertes y corpulentos. Las primeras diferencias ser\u00edan peque\u00f1\u00edsimas; pero en el transcurso del tiempo, por la selecci\u00f3n continuada de caballos m\u00e1s veloces en un caso, y m\u00e1s fuertes en otro, las diferencias se har\u00edan mayores y se distinguir\u00edan como formando dos sub-razas. Por \u00faltimo, despu\u00e9s de siglos, estas dos sub-razas llegar\u00edan a convertirse en dos razas distintas y bien establecidas. Al hacerse mayor la diferencia, los individuos inferiores con caracteres intermedios, que no fuesen ni muy veloces ni muy corpulentos, no se utilizar\u00edan para la cr\u00eda y, de este modo, han tendido a desaparecer. Vemos, pues, en las producciones del hombre la acci\u00f3n de lo que puede llamarse el principio de divergencia, produciendo diferencias, primero apenas apreciables, que aumentan continuamente, y que las razas se separan, por sus caracteres, unas de otras y tambi\u00e9n del tronco com\u00fan.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":" El contenido de este p\u00e1rrafo pertenece enteramente al cap\u00edtulo primero. Nada semejante a lo que ocurre en una granja tiene lugar en la naturaleza. Adem\u00e1s, en las granjas no se producen nuevas especies. 160. As has always been my practice, I have sought light on this head from our domestic productions. We shall here find something analogous. It will be admitted that the production of races so different as short-horn and Hereford cattle, race and cart horses, the several breeds of pigeons, etc., could never have been effected by the mere chance accumulation of similar\u2026<\/p>\n","protected":false},"author":86,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"ngg_post_thumbnail":0},"categories":[467,14321],"tags":[],"blocksy_meta":{"styles_descriptor":{"styles":{"desktop":"","tablet":"","mobile":""},"google_fonts":[],"version":4}},"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.madrimasd.org\/blogs\/biologia_pensamiento\/wp-json\/wp\/v2\/posts\/135168"}],"collection":[{"href":"https:\/\/www.madrimasd.org\/blogs\/biologia_pensamiento\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.madrimasd.org\/blogs\/biologia_pensamiento\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.madrimasd.org\/blogs\/biologia_pensamiento\/wp-json\/wp\/v2\/users\/86"}],"replies":[{"embeddable":true,"href":"https:\/\/www.madrimasd.org\/blogs\/biologia_pensamiento\/wp-json\/wp\/v2\/comments?post=135168"}],"version-history":[{"count":2,"href":"https:\/\/www.madrimasd.org\/blogs\/biologia_pensamiento\/wp-json\/wp\/v2\/posts\/135168\/revisions"}],"predecessor-version":[{"id":136736,"href":"https:\/\/www.madrimasd.org\/blogs\/biologia_pensamiento\/wp-json\/wp\/v2\/posts\/135168\/revisions\/136736"}],"wp:attachment":[{"href":"https:\/\/www.madrimasd.org\/blogs\/biologia_pensamiento\/wp-json\/wp\/v2\/media?parent=135168"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.madrimasd.org\/blogs\/biologia_pensamiento\/wp-json\/wp\/v2\/categories?post=135168"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.madrimasd.org\/blogs\/biologia_pensamiento\/wp-json\/wp\/v2\/tags?post=135168"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}