{"product_id":"2940012308412","title":"THE ORIGIN OF SPECIES 6th EDITION","description":"CHAPTER I. VARIATION UNDER DOMESTICATION.\u003cbr\u003e\u003cbr\u003e Causes of Variability--Effects of Habit and the use and disuse of\u003cbr\u003e Parts--Correlated Variation--Inheritance--Character of Domestic\u003cbr\u003e Varieties--Difficulty of distinguishing between Varieties and\u003cbr\u003e Species--Origin of Domestic Varieties from one or more Species--Domestic\u003cbr\u003e Pigeons, their Differences and Origin--Principles of Selection,\u003cbr\u003e anciently followed, their Effects--Methodical and Unconscious\u003cbr\u003e Selection--Unknown Origin of our Domestic Productions--Circumstances\u003cbr\u003e favourable to Man's power of Selection.\u003cbr\u003e\u003cbr\u003e\u003cbr\u003eCAUSES OF VARIABILITY.\u003cbr\u003e\u003cbr\u003eWhen we compare the individuals of the same variety or sub-variety of\u003cbr\u003eour older cultivated plants and animals, one of the first points which\u003cbr\u003estrikes us is, that they generally differ more from each other than do\u003cbr\u003ethe individuals of any one species or variety in a state of nature. And\u003cbr\u003eif we reflect on the vast diversity of the plants and animals which have\u003cbr\u003ebeen cultivated, and which have varied during all ages under the most\u003cbr\u003edifferent climates and treatment, we are driven to conclude that this\u003cbr\u003egreat variability is due to our domestic productions having been raised\u003cbr\u003eunder conditions of life not so uniform as, and somewhat different from,\u003cbr\u003ethose to which the parent species had been exposed under nature. There\u003cbr\u003eis, also, some probability in the view propounded by Andrew Knight, that\u003cbr\u003ethis variability may be partly connected with excess of food. It seems\u003cbr\u003eclear that organic beings must be exposed during several generations to\u003cbr\u003enew conditions to cause any great amount of variation; and that, when\u003cbr\u003ethe organisation has once begun to vary, it generally continues varying\u003cbr\u003efor many generations. No case is on record of a variable organism\u003cbr\u003eceasing to vary under cultivation. Our oldest cultivated plants, such\u003cbr\u003eas wheat, still yield new varieties: our oldest domesticated animals are\u003cbr\u003estill capable of rapid improvement or modification.\u003cbr\u003e\u003cbr\u003eAs far as I am able to judge, after long attending to the subject, the\u003cbr\u003econditions of life appear to act in two ways--directly on the whole\u003cbr\u003eorganisation or on certain parts alone and in directly by affecting the\u003cbr\u003ereproductive system. With respect to the direct action, we must bear in\u003cbr\u003emind that in every case, as Professor Weismann has lately insisted,\u003cbr\u003eand as I have incidently shown in my work on \"Variation under\u003cbr\u003eDomestication,\" there are two factors: namely, the nature of the\u003cbr\u003eorganism and the nature of the conditions. The former seems to be much\u003cbr\u003ethe more important; for nearly similar variations sometimes arise under,\u003cbr\u003eas far as we can judge, dissimilar conditions; and, on the other hand,\u003cbr\u003edissimilar variations arise under conditions which appear to be\u003cbr\u003enearly uniform. The effects on the offspring are either definite or in\u003cbr\u003edefinite. They may be considered as definite when all or nearly all the\u003cbr\u003eoffspring of individuals exposed to certain conditions during several\u003cbr\u003egenerations are modified in the same manner. It is extremely difficult\u003cbr\u003eto come to any conclusion in regard to the extent of the changes which\u003cbr\u003ehave been thus definitely induced. There can, however, be little doubt\u003cbr\u003eabout many slight changes, such as size from the amount of food,\u003cbr\u003ecolour from the nature of the food, thickness of the skin and hair from\u003cbr\u003eclimate, etc. Each of the endless variations which we see in the plumage\u003cbr\u003eof our fowls must have had some efficient cause; and if the same cause\u003cbr\u003ewere to act uniformly during a long series of generations on many\u003cbr\u003eindividuals, all probably would be modified in the same manner. Such\u003cbr\u003efacts as the complex and extraordinary out growths which variably\u003cbr\u003efollow from the insertion of a minute drop of poison by a gall-producing\u003cbr\u003einsect, shows us what singular modifications might result in the case of\u003cbr\u003eplants from a chemical change in the nature of the sap.\u003cbr\u003e\u003cbr\u003eIn definite variability is a much more common result of changed\u003cbr\u003econditions than definite variability, and has probably played a more\u003cbr\u003eimportant part in the formation of our domestic races. We see in\u003cbr\u003edefinite variability in the endless slight peculiarities which\u003cbr\u003edistinguish the individuals of the same species, and which cannot be\u003cbr\u003eaccounted for by inheritance from either parent or from some more remote\u003cbr\u003eancestor. Even strongly-marked differences occasionally appear in the\u003cbr\u003eyoung of the same litter, and in seedlings from the same seed-capsule.\u003cbr\u003eAt long intervals of time, out of millions of individuals reared in the\u003cbr\u003esame country and fed on nearly the same food, deviations of structure so\u003cbr\u003estrongly pronounced as to deserve to be called monstrosities arise; but\u003cbr\u003emonstrosities cannot be separated by any distinct line from slighter\u003cbr\u003evariations.","brand":"SAP","offers":[{"title":"Default Title","offer_id":47165467295984,"sku":"2940012308412","price":0.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0737\/7593\/9824\/files\/2940012308412_p0.jpg?v=1763554514","url":"https:\/\/shop-qa.barnesandnoble.com\/products\/2940012308412","provider":"Barnes \u0026 Noble (DEV)","version":"1.0","type":"link"}