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  • 熊黛林晒双胞胎女儿艺术照
    美要限制AI软件出口,专家:将激发中国自研 2020-08-03 12:28:56 关键字:娱乐   Voices
  • 中国海关:7天进口口罩5622.8万个,确保通关
    湖北红十字会该“委屈”吗? 2020-07-24 12:28:56 关键字:新闻 据菲媒ABS-CBN新闻报道,当地警方10日已确认,被绑架女子名叫周梅(音译),于9日晚9点多被两名男子拖进一辆车牌为LSA-880的灰色面包车。
  • 电竞魔幻现实:主播身价过亿 电竞小镇很难
    外媒记者能否进入武汉报道? 外交部:遵守有关规定 2020-07-19 12:28:56 关键字:财经 本轮融资将主要用于产品优化、线下门店扩张。
  • 迷路老人接通老伴电话大哭:没你没法过
    平成时代落幕!日本明仁天皇正式退位 2020-08-07 12:28:56 关键字:汽车 展开全文目前,特斯拉除了上海基地外,全部在美国本土生产。
  • 病情加重、核酸
    林书豪遭全场包夹拿16分 孙悦送追身大帽赢五棵松欢呼 2020-07-30 12:28:56 关键字:美容 12月初,记者下载爱又米App,很快接到来自杭州的电话。
  • 武汉通报:无新增新型冠状病毒感染的肺炎病例
    买房可打5折!深圳住房新政让“深漂”有盼了? 2020-08-01 12:28:56 关键字:科普 2018年,京东商城确立了以信赖为基础、以客户为中心的价值创造的经营理念。
  • 孟晚舟案首轮引渡聆讯解析:控辩争议点何在?后续有何走向?
    国务院:涉及缓报、瞒报、漏报疫情等行为将严肃处理 2020-07-24 12:28:56 关键字:科普 平顶山市红十字人道救援队相关负责人杜先生向新京报记者称,通过连续3天搜寻,女生最后现身地点,位于一公园的门口,有目击者见到。
  • 5个小贴士帮你重新振作
    节后股市或有重大转变 2020-08-03 12:28:56 关键字:漫画 班固(公元32-92年),字孟坚,扶风安陵(今陕西省咸阳市)人。东汉杰出的历史学家和文学家。他的《汉书》是我国第一部断代史,为后世封建王朝官修正史的楷模(对此将有专章介绍)。作为赋家,他的创作活动主要表现在身体力行地提倡散体大赋上。班固有浓厚的忠于皇室的正统思想。
  • 亚马逊中国官网挂了?回应:技术部门已着手处理
    习近平主持政治局会议 研究加强疫情防控工作 2020-07-31 12:28:56 关键字:观点 不论是针对不合格研究生,还是清退92名留学生,都说明对学生的学习过程性评价和淘汰机制正越来越严格,也渐成常态。
  • 大雾黄色预警:冀豫鲁川新局地能见度不足50米
    特朗普拒绝握手、佩洛西手撕演讲稿,美总统议长互撕成热点 2020-08-02 12:28:56 关键字:咨询 在这次苗民大起义中,“逐客民、复故地”是个有号召力的战斗口号,它主要是打击清朝官吏和掠夺苗民田地的汉族地主。汉族农民、手工业者、小商贩却有不少人参加了苗民起义。《黔南识略》总结说,石柳邓、白老寅等先后起义,“实亦受愚于汉奸,非尽其性好仇杀也”。汉族人民久居苗地营生,“若夫与苗渐狎,而诡为苗语、苗装,以通婚姻者,俗为之变苗,实则乱民也”。
  • 美国总统大选初选正式开启 特朗普将发表国情咨文
    李霄鹏:足协杯鲁能将轮换七八个人 给更多年轻人机会 2020-07-20 12:28:56 关键字:图片   I think these views further explain what has sometimes been noticed namely that we know nothing about the origin or history of any of our domestic breeds. But, in fact, a breed, like a dialect of a language, can hardly be said to have had a definite origin. A man preserves and breeds from an individual with some slight deviation of structure, or takes more care than usual in matching his best animals and thus improves them, and the improved individuals slowly spread in the immediate neighbourhood. But as yet they will hardly have a distinct name, and from being only slightly valued, their history will be disregarded. When further improved by the same slow and gradual process, they will spread more widely, and will get recognised as something distinct and valuable, and will then probably first receive a provincial name. In semi-civilised countries, with little free communication, the spreading and knowledge of any new sub-breed will be a slow process. As soon as the points of value of the new sub-breed are once fully acknowledged, the principle, as I have called it, of unconscious selection will always tend, perhaps more at one period than at another, as the breed rises or falls in fashion, perhaps more in one district than in another, according to the state of civilisation of the inhabitants slowly to add to the characteristic features of the breed, whatever they may be. But the chance will be infinitely small of any record having been preserved of such slow, varying, and insensible changes.I must now say a few words on the circumstances, favourable, or the reverse, to man's power of selection. A high degree of variability is obviously favourable, as freely giving the materials for selection to work on; not that mere individual differences are not amply sufficient, with extreme care, to allow of the accumulation of a large amount of modification in almost any desired direction. But as variations manifestly useful or pleasing to man appear only occasionally, the chance of their appearance will be much increased by a large number of individuals being kept; and hence this comes to be of the highest importance to success. On this principle Marshall has remarked, with respect to the sheep of parts of Yorkshire, that 'as they generally belong to poor people, and are mostly in small lots, they never can be improved.' On the other hand, nurserymen, from raising large stocks of the same plants, are generally far more successful than amateurs in getting new and valuable varieties. The keeping of a large number of individuals of a species in any country requires that the species should be placed under favourable conditions of life, so as to breed freely in that country. When the individuals of any species are scanty, all the individuals, whatever their quality may be, will generally be allowed to breed, and this will effectually prevent selection. But probably the most important point of all, is, that the animal or plant should be so highly useful to man, or so much valued by him, that the closest attention should be paid to even the slightest deviation in the qualities or structure of each individual. Unless such attention be paid nothing can be effected. I have seen it gravely remarked, that it was most fortunate that the strawberry began to vary just when gardeners began to attend closely to this plant. No doubt the strawberry had always varied since it was cultivated, but the slight varieties had been neglected. As soon, however, as gardeners picked out individual plants with slightly larger, earlier, or better fruit, and raised seedlings from them, and again picked out the best seedlings and bred from them, then, there appeared (aided by some crossing with distinct species) those many admirable varieties of the strawberry which have been raised during the last thirty or forty years.In the case of animals with separate sexes, facility in preventing crosses is an important element of success in the formation of new races, at least, in a country which is already stocked with other races. In this respect enclosure of the land plays a part. Wandering savages or the inhabitants of open plains rarely possess more than one breed of the same species. Pigeons can be mated for life, and this is a great convenience to the fancier, for thus many races may be kept true, though mingled in the same aviary; and this circumstance must have largely favoured the improvement and formation of new breeds. Pigeons, I may add, can be propagated in great numbers and at a very quick rate, and inferior birds may be freely rejected, as when killed they serve for food. On the other hand, cats, from their nocturnal rambling habits, cannot be matched, and, although so much valued by women and children, we hardly ever see a distinct breed kept up; such breeds as we do sometimes see are almost always imported from some other country, often from islands. Although I do not doubt that some domestic animals vary less than others, yet the rarity or absence of distinct breeds of the cat, the donkey, peacock, goose, &c., may be attributed in main part to selection not having been brought into play: in cats, from the difficulty in pairing them; in donkeys, from only a few being kept by poor people, and little attention paid to their breeding; in peacocks, from not being very easily reared and a large stock not kept; in geese, from being valuable only for two purposes, food and feathers, and more especially from no pleasure having been felt in the display of distinct breeds.To sum up on the origin of our Domestic Races of animals and plants. I believe that the conditions of life, from their action on the reproductive system, are so far of the highest importance as causing variability. I do not believe that variability is an inherent and necessary contingency, under all circumstances, with all organic beings, as some authors have thought. The effects of variability are modified by various degrees of inheritance and of reversion. Variability is governed by many unknown laws, more especially by that of correlation of growth. Something may be attributed to the direct action of the conditions of life. Something must be attributed to use and disuse. The final result is thus rendered infinitely complex. In some cases, I do not doubt that the intercrossing of species, aboriginally distinct, has played an important part in the origin of our domestic productions. When in any country several domestic breeds have once been established, their occasional intercrossing, with the aid of selection, has, no doubt, largely aided in the formation of new sub-breeds; but the importance of the crossing of varieties has, I believe, been greatly exaggerated, both in regard to animals and to those plants which are propagated by seed. In plants which are temporarily propagated by cuttings, buds, &c., the importance of the crossing both of distinct species and of varieties is immense; for the cultivator here quite disregards the extreme variability both of hybrids and mongrels, and the frequent sterility of hybrids; but the cases of plants not propagated by seed are of little importance to us, for their endurance is only temporary. Over all these causes of Change I am convinced that the accumulative action of Selection, whether applied methodically and more quickly, or unconsciously and more slowly, but more efficiently, is by far the predominant power.
  • 这些90后眼前,是战场,是重症隔离区
    英国52例新型冠状病毒肺炎疑似病例均为阴性 2020-07-19 12:28:56 关键字:法治 “We do things for other reasons than a profit motive, we do things because they are right and just,” Mr Cook growled. Whether in human rights, renewable energy or accessibility for people with special needs, “I don’t think about the bloody ROI,” Mr Cook said, in the same stern, uncompromising tone that Apple employees hope they never have to hear. “Just to be very straightforward with you, if that’s a hard line for you?.?.?.?then you should get out of the stock.”
  • 2020年彩票市场春节休市时间延长
    高速上行车飞来20斤铁块,春运将至这种事千万别出 2020-07-21 12:28:56 关键字:资讯 很多医美机构认为是冬天来了,我反而认为这是新的春天,就是要更加规范、更加守法,更加以核心技术来竞争,更加以优质的服务来面对,这样才能够保持行业长期健康可持续性发展。
  • 90%的人都缺乏的一种能力
    太空人单局四分带走比赛主场4-1逆转战胜印第安人 2020-07-23 12:28:56 关键字:美食   BEF0RE entering on the subject of this chapter, I must make a few preliminary remarks, to show how the struggle for existence bears on Natural Selection. It has been seen in the last chapter that amongst organic beings in a state of nature there is some individual variability; indeed I am not aware that this has ever been disputed. It is immaterial for us whether a multitude of doubtful forms be called species or sub-species or varieties; what rank, for instance, the two or three hundred doubtful forms of British plants are entitled to hold, if the existence of any well-marked varieties be admitted. But the mere existence of individual variability and of some few well-marked varieties, though necessary as the foundation for the work, helps us but little in understanding how species arise in nature. How have all those exquisite adaptations of one part of the organisation to another part, and to the conditions of life, and of one distinct organic being to another being, been perfected? We see these beautiful co-adaptations most plainly in the woodpecker and missletoe; and only a little less plainly in the humblest parasite which clings to the hairs of a quadruped or feathers of a bird; in the structure of the beetle which dives through the water; in the plumed seed which is wafted by the gentlest breeze; in short, we see beautiful adaptations everywhere and in every part of the organic world.Again, it may be asked, how is it that varieties, which I have called incipient species, become ultimately converted into good and distinct species, which in most cases obviously differ from each other far more than do the varieties of the same species? How do those groups of species, which constitute what are called distinct genera, and which differ from each other more than do the species of the same genus, arise? All these results, as we shall more fully see in the next chapter, follow inevitably from the struggle for life. Owing to this struggle for life, any variation, however slight and from whatever cause proceeding, if it be in any degree profitable to an individual of any species, in its infinitely complex relations to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring. The offspring, also, will thus have a better chance of surviving, for, of the many individuals of any species which are periodically born, but a small number can survive. I have called this principle, by which each slight variation, if useful, is preserved, by the term of Natural Selection, in order to mark its relation to man's power of selection. We have seen that man by selection can certainly produce great results, and can adapt organic beings to his own uses, through the accumulation of slight but useful variations, given to him by the hand of Nature. But Natural Selection, as we shall hereafter see, is a power incessantly ready for action, and is as immeasurably superior to man's feeble efforts, as the works of Nature are to those of Art.We will now discuss in a little more detail the struggle for existence. In my future work this subject shall be treated, as it well deserves, at much greater length. The elder De Candolle and Lyell have largely and philosophically shown that all organic beings are exposed to severe competition. In regard to plants, no one has treated this subject with more spirit and ability than W. Herbert, Dean of Manchester, evidently the result of his great horticultural knowledge. Nothing is easier than to admit in words the truth of the universal struggle for life, or more difficult at least I have found it so than constantly to bear this conclusion in mind. Yet unless it be thoroughly engrained in the mind, I am convinced that the whole economy of nature, with every fact on distribution, rarity, abundance, extinction, and variation, will be dimly seen or quite misunderstood. We behold the face of nature bright with gladness, we often see superabundance of food; we do not see, or we forget, that the birds which are idly singing round us mostly live on insects or seeds, and are thus constantly destroying life; or we forget how largely these songsters, or their eggs, or their nestlings are destroyed by birds and beasts of prey; we do not always bear in mind, that though food may be now superabundant, it is not so at all seasons of each recurring year.I should premise that I use the term Struggle for Existence in a large and metaphorical sense, including dependence of one being on another, and including (which is more important) not only the life of the individual, but success in leaving progeny. Two canine animals in a time of dearth, may be truly said to struggle with each other which shall get food and live. But a plant on the edge of a desert is said to struggle for life against the drought, though more properly it should be said to be dependent on the moisture. A plant which annually produces a thousand seeds, of which on an average only one comes to maturity, may be more truly said to struggle with the plants of the same and other kinds which already clothe the ground. The missletoe is dependent on the apple and a few other trees, but can only in a far-fetched sense be said to struggle with these trees, for if too many of these parasites grow on the same tree, it will languish and die. But several seedling missletoes, growing close together on the same branch, may more truly be said to struggle with each other. As the missletoe is disseminated by birds, its existence depends on birds; and it may metaphorically be said to struggle with other fruit-bearing plants, in order to tempt birds to devour and thus disseminate its seeds rather than those of other plants. In these several senses, which pass into each other, I use for convenience sake the general term of struggle for existence.A struggle for existence inevitably follows from the high rate at which all organic beings tend to increase. Every being, which during its natural lifetime produces several eggs or seeds, must suffer destruction during some period of its life, and during some season or occasional year, otherwise, on the principle of geometrical increase, its numbers would quickly become so inordinately great that no country could support the product. 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. It is the doctrine of Malthus applied with manifold force to the whole animal and vegetable kingdoms; for in this case there can be no artificial increase of food, and no prudential restraint from marriage. Although some species may be now increasing, more or less rapidly, in numbers, all cannot do so, for the world would not hold them.
  • 美国劝英国放弃华为 英首相:民众有权用最先进的科技
    强化IOT去家电化?家电头部企业正酝酿新格局 2020-08-05 12:28:56 关键字:武器 They leaped like deer, too, with a quick folding motion of the legs, drawn up and turned to one side with a sidelong twist of the body. I remembered the sprawling spread-eagle way in which some of the fellows used to come over the line--and tried to learn the trick. We did not easily catch up with these experts, however.
  • 变局中凝聚世界的思想引领
    习近平大国外交的中国智慧 2020-07-22 12:28:56 关键字:科普 普通人陪你唠嗑的音频内容,你可以当成是语音直播,你也可以把它当成一个纯语音秀场。