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  • 母亲为大一女儿招聘保姆洗衣做饭:孩子不会,我又没时间
    英国刚说5G能用华为,美国又来这招威胁 2020-08-02 10:44:56 关键字:疫苗 而且,我并不是想向你展示一些统计数据或什么神奇的公式来说服你选择一种生活方式而非另一种——显然,这种选择取决于你自己,而且我相信正在看这篇文章的每个人都有足够的判断力,能够综合考虑多种因素以及自己最看重的东西,然后在初创公司和大厂之间做一个选择——当然,两者都各有利弊。
  • 售7.58万-8.88万 吉利缤瑞新增三款车型
    生猪生产回暖势头显现(保供稳价在行动) 2020-08-07 10:44:56 关键字:汽车   "Well, what do you say to this?" asked Drouet, innocently, whileCarrie's mind bubbled with favourable replies.
  • 【武汉十四日】英雄的城市,你定能过关!
    中共中央政治局召开会议 习近平主持 2020-07-27 10:44:56 关键字:教育 上赛季,桑普多利亚老将夸利亚雷拉也追平了巴蒂斯图塔。
  • 真正靠实力吃肉!桂林一班级奖励优秀学生:每人两斤猪肉
    多人购票无法上火车?官方:有人到站不下车致超载 2020-07-26 10:44:56 关键字:科技 在此之前,白云先生曾在中国香港就职于麦肯锡公司,担任咨询顾问,辅助多家金融、电信、互联网和工业客户企业制定增长和数字化转型战略。
  • 安倍称不考虑再连任自民党总裁,列出自己中意的四位继任人选
    男子做心肺复苏压断老太12根肋骨 被告后法院力挺 2020-07-30 10:44:56 关键字:财经 完善游戏广告的立法,明确游戏广告不得含有的内容,才能有效规范游戏广告
  •  CBA-浙江广厦客场对阵上海 刘铮强行攻击篮筐
    香港“黄丝”被澳门拒绝入境,有人直言“活该” 2020-07-29 10:44:56 关键字:健康   Noemon then went back to his father's house, but Antinous andEurymachus were very angry. They told the others to leave off playing,and to come and sit down along with themselves. When they came,Antinous son of Eupeithes spoke in anger. His heart was black withrage, and his eyes flashed fire as he said:
  • 伊朗回应导弹击落乌航客机传闻
    华为2019年智能手机发货量超2.4亿台 2020-07-27 10:44:56 关键字:汽车 可第二天柳传志又接到密报,说掌握着1700万资金的企业部,有人打算携款潜逃。
  • 白岩松陈道明一开口 这台没有现场观众的元宵晚会看哭网友
    疫病斗争史中,那些不能忘却的人和事 2020-07-23 10:44:56 关键字:海事 那么会不会是和地震有关呢?咸阳市秦都区地震工作办公室主任李靠社对此也予以否定:这块地方,从地质构造上来说,不可能有断裂,所以说水温升高不可能是地壳深部热水上来。
  • 有道Q3财报解读:网易有道,道而不径
    4月份70个大中城市有67城新房价格上涨 商住价格稳中略升 2020-07-28 10:44:56 关键字:汽车 It is a struggle for power contained by understandings and institutions.
  • 美总统选举首场初选陷入计票混乱,内部数据显示拜登惨败
    四闺蜜首秀小S最显老? 2020-07-27 10:44:56 关键字:防控 警方赶到时,发现沃尔克正在殴打55岁的受害人唐纳德·安博那,沃尔克的狗在旁不断撕咬着他
  • 泰国举行国王加冕大典彩排 仪式预计耗资10亿泰铢
    微信扫一扫学习更高效 2020-08-07 10:44:56 关键字:文化 据国家新闻出版广电总局介绍,中国的电影票房收益在2017年上涨了13.45%,达559亿元(86亿美元),国产影片为该市场做了53.84%的贡献。
  • 习近平年度“金句”:我将无我,不负人民
    从轻处罚,法院为何仍对“乐清失联男孩”母亲判实刑? 2020-07-23 10:44:56 关键字:健康 一条好的规则是:如果一个页面不能获得平均每个月100的浏览量,那么就可以考虑删掉它了。
  • “中国功率器件领路人”陈星弼院士逝世,享年89岁
    疫情之下,蔚来销量还行吗? 2020-07-21 10:44:56 关键字:海事   I jumped up, took my muff and umbrella, and hastened into theinn-passage: a man was standing by the open door, and in thelamp-lit street I dimly saw a one-horse conveyance.
  • 家居众筹成为一大热点 参与仍需全方位考量
    春节假期是否会进一步延长?卫健委:关注疫情变化 2020-07-24 10:44:56 关键字:科普   When we see any part or organ developed in a remarkable degree or manner in any species, the fair presumption is that it is of high importance to that species; nevertheless the part in this case is eminently liable to variation. Why should this be so? On the view that each species has been independently created, with all its parts as we now see them, I can see no explanation. But on the view that groups of species have descended from other species, and have been modified through natural selection, I think we can obtain some light. In our domestic animals, if any part, or the whole animal, be neglected and no selection be applied, that part (for instance, the comb in the Dorking fowl) or the whole breed will cease to have a nearly uniform character. The breed will then be said to have degenerated. In rudimentary organs, and in those which have been but little specialized for any particular purpose, and perhaps in polymorphic groups, we see a nearly parallel natural case; for in such cases natural selection either has not or cannot come into full play, and thus the organisation is left in a fluctuating condition. But what here more especially concerns us is, that in our domestic animals those points, which at the present time are undergoing rapid change by continued selection, are also eminently liable to variation. Look at the breeds of the pigeon; see what a prodigious amount of difference there is in the beak of the different tumblers, in the beak and wattle of the different carriers, in the carriage and tail of our fantails, &c., these being the points now mainly attended to by English fanciers. Even in the sub-breeds, as in the short-faced tumbler, it is notoriously difficult to breed them nearly to perfection, and frequently individuals are born which depart widely from the standard. There may be truly said to be a constant struggle going on between, on the one hand, the tendency to reversion to a less modified state, as well as an innate tendency to further variability of all kinds, and, on the other hand, the power of steady selection to keep the breed true. In the long run selection gains the day, and we do not expect to fail so far as to breed a bird as coarse as a common tumbler from a good short-faced strain. But as long as selection is rapidly going on, there may always be expected to be much variability in the structure undergoing modification. It further deserves notice that these variable characters, produced by man's selection, sometimes become attached, from causes quite unknown to us, more to one sex than to the other, generally to the male sex, as with the wattle of carriers and the enlarged crop of pouters.Now let us turn to nature. When a part has been developed in an extraordinary manner in any one species, compared with the other species of the same genus, we may conclude that this part has undergone an extraordinary amount of modification, since the period when the species branched off from the common progenitor of the genus. This period will seldom be remote in any extreme degree, as species very rarely endure for more than one geological period. An extraordinary amount of modification implies an unusually large and long-continued amount of variability, which has continually been accumulated by natural selection for the benefit of the species. But as the variability of the extraordinarily-developed part or organ has been so great and long-continued within a period not excessively remote, we might, as a general rule, expect still to find more variability in such parts than in other parts of the organisation, which have remained for a much longer period nearly constant. And this, I am convinced, is the case. That the struggle between natural selection on the one hand, and the tendency to reversion and variability on the other hand, will in the course of time cease; and that the most abnormally developed organs may be made constant, I can see no reason to doubt. Hence when an organ, however abnormal it may be, has been transmitted in approximately the same condition to many modified descendants, as in the case of the wing of the bat, it must have existed, according to my theory, for an immense period in nearly the same state; and thus it comes to be no more variable than any other structure. It is only in those cases in which the modification has been comparatively recent and extraordinarily great that we ought to find the generative variability, as it may be called, still present in a high degree. For in this case the variability will seldom as yet have been fixed by the continued selection of the individuals varying in the required manner and degree, and by the continued rejection of those tending to revert to a former and less modified condition.The principle included in these remarks may be extended. It is notorious that specific characters are more variable than generic. To explain by a simple example what is meant. If some species in a large genus of plants had blue flowers and some had red, the colour would be only a specific character, and no one would be surprised at one of the blue species varying into red, or conversely; but if all the species had blue flowers, the colour would become a generic character, and its variation would be a more unusual circumstance. I have chosen this example because an explanation is not in this case applicable, which most naturalists would advance, namely, that specific characters are more variable than generic, because they are taken from parts of less physiological importance than those commonly used for classing genera. I believe this explanation is partly, yet only indirectly, true; I shall, however, have to return to this subject in our chapter on Classification. It would be almost superfluous to adduce evidence in support of the above statement, that specific characters are more variable than generic; but I have repeatedly noticed in works on natural history, that when an author has remarked with surprise that some important organ or part, which is generally very constant throughout large groups of species, has differed considerably in closely-allied species, that it has, also, been variable in the individuals of some of the species. And this fact shows that a character, which is generally of generic value, when it sinks in value and becomes only of specific value, often becomes variable, though its physiological importance may remain the same. Something of the same kind applies to monstrosities: at least Is. Geoffroy St. Hilaire seems to entertain no doubt, that the more an organ normally differs in the different species of the same group, the more subject it is to individual anomalies.On the ordinary view of each species having been independently created, why should that part of the structure, which differs from the same part in other independently-created species of the same genus, be more variable than those parts which are closely alike in the several species? I do not see that any explanation can be given. But on the view of species being only strongly marked and fixed varieties, we might surely expect to find them still often continuing to vary in those parts of their structure which have varied within a moderately recent period, and which have thus come to differ. Or to state the case in another manner: the points in which all the species of a genus resemble each other, and in which they differ from the species of some other genus, are called generic characters; and these characters in common I attribute to inheritance from a common progenitor, for it can rarely have happened that natural selection will have modified several species, fitted to more or less widely-different habits, in exactly the same manner: and as these so-called generic characters have been inherited from a remote period, since that period when the species first branched off from their common progenitor, and subsequently have not varied or come to differ in any degree, or only in a slight degree, it is not probable that they should vary at the present day. On the other hand, the points in which species differ from other species of the same genus, are called specific characters; and as these specific characters have varied and come to differ within the period of the branching off of the species from a common progenitor, it is probable that they should still often be in some degree variable, at least more variable than those parts of the organisation which have for a very long period remained constant.In connexion with the present subject, I will make only two other remarks. I think it will be admitted, without my entering on details, that secondary sexual characters are very variable; I think it also will be admitted that species of the same group differ from each other more widely in their secondary sexual characters, than in other parts of their organisation; compare, for instance, the amount of difference between the males of gallinaceous birds, in which secondary sexual characters are strongly displayed, with the amount of difference between their females; and the truth of this proposition will be granted. The cause of the original variability of secondary sexual characters is not manifest; but we can see why these characters should not have been rendered as constant and uniform as other parts of the organisation; for secondary sexual characters have been accumulated by sexual selection, which is less rigid in its action than ordinary selection, as it does not entail death, but only gives fewer offspring to the less favoured males. Whatever the cause may be of the variability of secondary sexual characters, as they are highly variable, sexual selection will have had a wide scope for action, and may thus readily have succeeded in giving to the species of the same group a greater amount of difference in their sexual characters, than in other parts of their structure.It is a remarkable fact, that the secondary sexual differences between the two sexes of the same species are generally displayed in the very same parts of the organisation in which the different species of the same genus differ from each other. Of this fact I will give in illustration two instances, the first which happen to stand on my list; and as the differences in these cases are of a very unusual nature, the relation can hardly be accidental. The same number of joints in the tarsi is a character generally common to very large groups of beetles, but in the Engidae, as Westwood has remarked, the number varies greatly; and the number likewise differs in the two sexes of the same species: again in fossorial hymenoptera, the manner of neuration of the wings is a character of the highest importance, because common to large groups; but in certain genera the neuration differs in the different species, and likewise in the two sexes of the same species. This relation has a clear meaning on my view of the subject: I look at all the species of the same genus as having as certainly descended from the same progenitor, as have the two sexes of any one of the species. Consequently, whatever part of the structure of the common progenitor, or of its early descendants, became variable; variations of this part would it is highly probable, be taken advantage of by natural and sexual selection, in order to fit the several species to their several places in the economy of nature, and likewise to fit the two sexes of the same species to each other, or to fit the males and females to different habits of life, or the males to struggle with other males for the possession of the females.Finally, then, I conclude that the greater variability of specific characters, or those which distinguish species from species, than of generic characters, or those which the species possess in common; that the frequent extreme variability of any part which is developed in a species in an extraordinary manner in comparison with the same part in its congeners; and the not great degree of variability in a part, however extraordinarily it may be developed, if it be common to a whole group of species; that the great variability of secondary sexual characters, and the great amount of difference in these same characters between closely allied species; that secondary sexual and ordinary specific differences are generally displayed in the same parts of the organisation, are all principles closely connected together. All being mainly due to the species of the same group having descended from a common progenitor, from whom they have inherited much in common, to parts which have recently and largely varied being more likely still to go on varying than parts which have long been inherited and have not varied, to natural selection having more or less completely, according to the lapse of time, overmastered the tendency to reversion and to further variability, to sexual selection being less rigid than ordinary selection, and to variations in the same parts having been accumulated by natural and sexual selection, and thus adapted for secondary sexual, and for ordinary specific purposes.Distinct species present analogous variations; and a variety of one species often assumes some of the characters of an allied species, or reverts to some of the characters of an early progenitor.
  • 习近平致函萨勒 祝贺中非合作论坛成立20周年
    新西兰火山喷发已致16人死亡,新总理:问责调查或需一年 2020-07-19 10:44:56 关键字:更多   So the bird was sent for and the case laid before him.
  • 疫情防控期间停止影视剧拍摄
    台“黑鹰”事故中“参谋总长”获救 2020-07-24 10:44:56 关键字:台湾   "That's the thing," said Drouet. "Now pay for it."