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物种起源|The Origin of Species

第六章　学说的难点|CHAPTER VI　DIFFICULTIES ON THEORY

属类： 双语小说 【分类】其他读物 阅读：[7138]
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伴随着变异的遗传学说的难点——过渡——过渡变种的不存在或稀有——生活习性的过渡——同一物种中的多样化习性——具有与近缘物种极其不同习性的物种——极端完善的器官——过渡方式——难点的个案——自然界没有飞跃——重要性小的器官——器官并不统统都是绝对完善的——自然选择学说所包括的模式统一法则和生存条件法则

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Difficulties on the theory of descent with modification— Transitions—Absence or rarity of transitional varieties—Transitions in habits of life—Diversified habits in the same species—Species with habits widely different from those of their allies—Organs of extreme perfection—Means of transition—Cases of difficulty— Natura non facit saltum—Organs of small importance—Organs not in all cases absolutely perfect—The law of Unity of Type and of the Conditions of Existence embraced by the theory of Natural Selection

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读者远在读到本章之前，想来已经遇到了成堆的难点。有些难点很严重，今日我想到它们还不免触目惊心。但是，据我所知，大多数的难点只是表面现象，而那些真实的难点，我想，对于这一学说也不是致命的。

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Long before having arrived at this part of my work, a crowd of difficulties will have occurred to the reader. Some of them are so grave that to this day I can never reflect on them without being staggered; but, to the best of my judgment, the greater number are only apparent, and those that are real are not, I think, fatal to my theory.

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这些难点和异议可以分作以下几类：第一，如果物种是从其他物种一点点地无缝逐渐遗传变成的，那么，为什么我们没有到处看到无数的过渡类型呢？为什么物种恰像我们所见到的那样界限分明，而整个自然界不呈混乱状态呢？

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These difficulties and objections may be classed under the following heads:—Firstly, why, if species have descended from other species by insensibly fine gradations, do we not everywhere see innumerable transitional forms? Why is not all nature in confusion instead of the species being, as we see them, well defined?

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第二，一种动物，比方说，具有像蝙蝠那样构造和习性的动物，有可能由别种习性大相径庭的动物变化而成吗？我们能够相信自然选择一方面可以产生出很不重要的器官，如只能用作拂蝇的长颈鹿的尾巴，另一方面，可以产生出像眼睛那样的奇妙器官吗？眼睛无法模仿的完美性，我们至今没有充分领悟。

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Secondly, is it possible that an animal having, for instance, the structure and habits of a bat, could have been formed by the modification of some animal with wholly different habits? Can we believe that natural selection could produce, on the one hand, organs of trifling importance, such as the tail of a giraffe, which serves as a fly-flapper, and, on the other hand, organs of such wonderful structure, as the eye, of which we hardly as yet fully understand the inimitable perfection?

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第三，本能能够通过自然选择获得和改变吗？引导蜜蜂营造蜂房的神奇本能实际上预示着学识渊博的数学家的发现，对此我们应当做何解说呢？

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Thirdly, can instincts be acquired and modified through natural selection? What shall we say to so marvellous an instinct as that which leads the bee to make cells, which have practically anticipated the discoveries of profound mathematicians?

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第四，对于物种杂交时的不育性及其后代的不育性，对于变种杂交时的能育性的不受损害，我们怎样解释呢？

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Fourthly, how can we account for species, when crossed, being sterile and producing sterile offspring, whereas, when varieties are crossed, their fertility is unimpaired?

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前两项将在这里讨论；本能和杂种状态（hybridism）在另外的两章讨论。

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The two first heads shall be here discussed—Instinct and Hybridism in separate chapters.

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论过渡变种的不存在或稀有。——因为自然选择的作用仅仅在于保存有利的变异，所以在充满生物的区域内，每一新的类型都倾向于代替并且最后消灭比自己改进较少的亲类型以及与它竞争而受益较少的类型。因此我们看到，灭绝和自然选择是并行不悖的。所以，如果我们把每一物种都看作是从某未知类型传下来的，那么亲种和一切过渡的变种，一般在这个新类型的形成完善过程中就已经被消灭了。

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On the absence or rarity of transitional varieties.—As natural selection acts solely by the preservation of profitable modifications, each new form will tend in a fully-stocked country to take the place of, and finally to exterminate, its own less improved parent or other less-favoured forms with which it comes into competition. Thus extinction and natural selection will, as we have seen, go hand in hand. Hence, if we look at each species as descended from some other unknown form, both the parent and all the transitional varieties will generally have been exterminated by the very process of formation and perfection of the new form.

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但是，依这种理论，无数过渡的类型一定曾经存在过，为什么我们看不到它们大量埋存在地壳里呢？在“论地质记录的不完全”一章里讨论这一问题，将会更加便利；我在这里只说明，我认为关于这一问题的答案主要在于地质记录的不完全实非一般所能想象。记录不全的主要原因是生物并不潜居深海，其遗体只有在足够厚实宽广的沉积体中才能嵌入保存到未来年代，抵御大量的未来剥蚀；而这种含化石的沉积体只有在缓慢下沉的浅海床上大量沉积时才能积累起来。这种偶发条件可遇不可求，万年才能遇到一次。海床可静止可抬升，沉积较少的，地质史就出现空白了。地壳是个巨大的博物馆，但自然界的收藏是在长久的间隔时期中间歇进行的。

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But, as by this theory innumerable transitional forms must have existed, why do we not find them embedded in countless numbers in the crust of the earth? It will be much more convenient to discuss this question in the chapter on the imperfection of the geological record; and I will here only state that I believe the answer mainly lies in the record being incomparably less perfect than is generally supposed; the imperfection of the record being chiefly due to organic beings not inhabiting profound depths of the sea, and to their remains being embedded and preserved to a future age only in masses of sediment sufficiently thick and extensive to withstand an enormous amount of future degradation; and such fossiliferous masses can be accumulated only where much sediment is deposited on the shallow bed of the sea, whilst it slowly subsides. These contingencies will concur only rarely, and after enormously long intervals. Whilst the bed of the sea is stationary or is rising, or when very little sediment is being deposited, there will be blanks in our geological history. The crust of the earth is a vast museum; but the natural collections have been made only at intervals of time immensely remote.

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但是，可以主张，当若干亲缘密切的物种栖息在同一地域内时，确实应该在今日看到许多过渡类型才对。举一个简单的例子：当在大陆上从北往南旅行时，我们一般会时不时看到亲缘密切的或代表的物种显然在自然组成里占据着几乎相同的位置。这些代表的物种常常相遇交叉，此消彼长，终于彼此淘汰。但如果在这些物种相混的地方来比较它们，就可以看出构造的各个细点一般都绝对不同，就像从各个物种的中心栖息地点采集来的标本一样。按照我的理论，这些近缘物种是从一个共同亲种传下来的；在变异的过程中，各个物种都已适应了自己区域里的生活条件，并淘汰消灭了原来的亲种以及一切连接过去和现在的过渡变种。因此，我们今日不应该希望在各地都遇到大量的过渡变种，虽然它们必定在那里存在过，并且可能以化石状态在那里埋存着。但是在具有中间生活条件的中间地带，为什么现在看不到密切连接的中间变种呢？这一难点在长久期间内颇使我惶惑，但是我想，它大体是能够解释的。

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But it may be urged that when several closely-allied species inhabit the same territory we surely ought to find at the present time many transitional forms. Let us take a simple case: in travelling from north to south over a continent, we generally meet at successive intervals with closely allied or representative species, evidently filling nearly the same place in the natural economy of the land. These representative species often meet and interlock; and as the one becomes rarer and rarer, the other becomes more and more frequent, till the one replaces the other. But if we compare these species where they intermingle, they are generally as absolutely distinct from each other in every detail of structure as are specimens taken from the metropolis inhabited by each. By my theory these allied species have descended from a common parent; and during the process of modification, each has become adapted to the conditions of life of its own region, and has supplanted and exterminated its original parent and all the transitional varieties between its past and present states. Hence we ought not to expect at the present time to meet with numerous transitional varieties in each region, though they must have existed there, and may be embedded there in a fossil condition. But in the intermediate region, having intermediate conditions of life, why do we not now find closely-linking intermediate varieties? This difficulty for a long time quite confounded me. But I think it can be in large part explained.

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第一，如果一个地方现在是连续的，就推论它长期也是连续的，对此应当极端慎重。地质学使我们相信：大多数的大陆，甚至在第三纪末期也还分裂成岛屿；这样的岛屿上没有中间变种在中间地带生存的可能性，不同的物种大概是分别形成的。由于地形和气候的变迁，现在连续的海面在最近以前的时期，一定远远不像今日那样连续和一致。但是我不取这条道路来逃避困难；因为我相信许多定义明确的物种是在本来严格连续的地面上形成的；虽然我并不怀疑现今连续地面的以前断离状态，对于新种形成，特别对于自由杂交而漫游的动物的新种形成，有着重要作用。

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In the first place we should be extremely cautious in inferring, because an area is now continuous, that it has been continuous during a long period. Geology would lead us to believe that almost every continent has been broken up into islands even during the later tertiary periods; and in such islands distinct species might have been separately formed without the possibility of intermediate varieties existing in the intermediate zones. By changes in the form of the land and of climate, marine areas now continuous must often have existed within recent times in a far less continuous and uniform condition than at present. But I will pass over this way of escaping from the difficulty; for I believe that many perfectly defined species have been formed on strictly continuous areas; though I do not doubt that the formerly broken condition of areas now continuous has played an important part in the formation of new species, more especially with freely-crossing and wandering animals.

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观察一下现今在广大地域内分布的物种，我们一般会看到它们在一个大界域内是相当多的，而在边界处就多少突然地逐渐稀少下来，最后终于消失。因此，两个代表物种之间的中立地带比起各自的独占地带，一般总是狭小的。在登山时我们可以看到同样的事实，有时正如德康多尔所说的，一种普通的高山植物非常突然地消失了，这是十分值得注意的。福布斯在用捞网采集器探查深海时，也曾注意到同样的事实。有些人把气候和物理的生活条件看作是分布的最重要因素，这等事实应该令人惊异，因为气候和高度或深度都是不知不觉地逐渐改变的。但是如果我们记得，几乎每一物种，甚至在分布的中心地方，倘没有竞争的物种，个体数目将巨幅增加；几乎一切物种不是吃别的物种便是被吃掉；总而言之，每一生物都与别的生物以极重要的方式直接间接地发生关系，那么我们就会知道，任何地方的生物分布范围决不单单决定于不知不觉地变化着的物理条件，而是大部分决定于其他物种的存在，依赖其他物种而生活，或者被其他物种所毁灭，或者与其他物种相竞争；由于这些物种都已经是定义分明的实物（不管是怎么形成的），没有被不可觉察的各级类型混淆在一起，任何一个物种的分布范围，因依存于其他物种的分布范围，都倾向于清晰的定义。此外，各个物种在分布范围的边缘上，个体数目生存较少，由于敌害、猎物数量的波动，或季节变动，将极易遭到彻底消灭；因此，它的地理分布范围的界限就更加清晰了。

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In looking at species as they are now distributed over a wide area, we generally find them tolerably numerous over a large territory, then becoming somewhat abruptly rarer and rarer on the confines, and finally disappearing. Hence the neutral territory between two representative species is generally narrow in comparison with the territory proper to each. We see the same fact in ascending mountains, and sometimes it is quite remarkable how abruptly, as Alph. De Candolle has observed, a common alpine species disappears. The same fact has been noticed by Forbes in sounding the depths of the sea with the dredge. To those who look at climate and the physical conditions of life as the all-important elements of distribution, these facts ought to cause surprise, as climate and height or depth graduate away insensibly. But when we bear in mind that almost every species, even in its metropolis, would increase immensely in numbers, were it not for other competing species; that nearly all either prey on or serve as prey for others; in short, that each organic being is either directly or indirectly related in the most important manner to other organic beings, we must see that the range of the inhabitants of any country by no means exclusively depends on insensibly changing physical conditions, but in large part on the presence of other species, on which it depends, or by which it is destroyed, or with which it comes into competition; and as these species are already defined objects (however they may have become so), not blending one into another by insensible gradations, the range of any one species, depending as it does on the range of others, will tend to be sharply defined. Moreover, each species on the confines of its range, where it exists in lessened numbers, will, during fluctuations in the number of its enemies or of its prey, or in the seasons, be extremely liable to utter extermination; and thus its geographical range will come to be still more sharply defined.

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亲缘的或代表的物种生存在连续的地域内时，各物种一般都有广大的分布范围，之间有比较狭小的中立地带，它们在那里会突然地越来越稀少；如果我的这个观点正确，那么又因为变种和物种没有本质上的区别，所以同样的法则大概可以应用于两者；如果我们假想让一个正在变异中的物种适应于一片广大区域，那势必要让两个变种适应于两片大区域，并且要让第三个变种适应于狭小的中间地带。结果，中间变种由于栖息在狭小的区域内，个体数目就较少；实际上，据我所能理解的来说，这一规律是适合于自然状态下的变种的。关于藤壶属（Balanus）里的显著变种的中间变种，我看到这一规律的显著例子。沃森先生、阿萨·格雷博士和沃拉斯顿先生给我的材料表明，当介于两个类型之间的中间变种存在的时候，其个体数目一般比所连接的两个类型要少得多。如果我们相信这些事实和推论，并且断定连接两个变种的变种个体，一般较所连接的类型少的话，那我想就能理解中间变种为什么不会存续很久——中间变种为什么照例比被原来所连接的那些类型灭绝和消失得早些。

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If I am right in believing that allied or representative species, when inhabiting a continuous area, are generally so distributed that each has a wide range, with a comparatively narrow neutral territory between them, in which they become rather suddenly rarer and rarer; then, as varieties do not essentially differ from species, the same rule will probably apply to both; and if we in imagination adapt a varying species to a very large area, we shall have to adapt two varieties to two large areas, and a third variety to a narrow intermediate zone. The intermediate variety, consequently, will exist in lesser numbers from inhabiting a narrow and lesser area; and practically, as far as I can make out, this rule holds good with varieties in a state of nature. I have met with striking instances of the rule in the case of varieties intermediate between well-marked varieties in the genus Balanus. And it would appear from information given me by Mr. Watson, Dr. Asa Gray, and Mr. Wollaston, that generally when varieties intermediate between two other forms occur, they are much rarer numerically than the forms which they connect. Now, if we may trust these facts and inferences, and therefore conclude that varieties linking two other varieties together have generally existed in lesser numbers than the forms which they connect, then, I think, we can understand why intermediate varieties should not endure for very long periods;—why as a general rule they should be exterminated and disappear, sooner than the forms which they originally linked together.

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如前所述，任何个体数目较少的类型，比个体数目多的类型，会遇到更大的灭绝机会；在这种情况下，中间类型极容易被两边存在着的亲缘密切的类型所侵犯。但我认为还有更加重要的理由：在我假定两个变种改变完善为两个不同物种的进一步变异过程中，个体数目较多的两个变种，由于栖息在较大的地域内，就比在狭小中间地带内个体数较少的中间变种占有强大优势。个体数较多的类型，比个体数较少的类型，在任何给定的时期内，都有更好的机会去呈现更有利的变异，以供自然选择利用。因此，较普通的类型在生活竞争里，就倾向于压倒淘汰较不普通的类型，因为后者的改变改良是比较缓慢的。我相信，如第二章所指出的，这一同样的原理也可说明为什么每一地区的普通物种比稀少的物种平均能呈现较多的特征显著的变种。可以举例说明我的意思，假定饲养着三个绵羊变种，一个适应于广大的山区；一个适应于比较狭小的丘陵地带；第三个适应于广阔的平原。假定这三处的居民都有同样的决心和技巧，利用选择来改良品种；此时，拥有多数羊的山区或平原饲养者，将有更多的机会，比拥有少数羊的狭小中间丘陵地带饲养者在改良品种上要快些；结果，改良的山地或平原品种就会很快代替改良较少的丘陵品种；这样，本来个体数目较多的这两个品种，便会彼此密切相接，而没有那被淘汰的丘陵中间变种夹在其中。

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For any form existing in lesser numbers would, as already remarked, run a greater chance of being exterminated than one existing in large numbers; and in this particular case the intermediate form would be eminently liable to the inroads of closely allied forms existing on both sides of it. But a far more important consideration, as I believe, is that, during the process of further modification, by which two varieties are supposed on my theory to be converted and perfected into two distinct species, the two which exist in larger numbers from inhabiting larger areas, will have a great advantage over the intermediate variety, which exists in smaller numbers in a narrow and intermediate zone. For forms existing in larger numbers will always have a better chance, within any given period, of presenting further favourable variations for natural selection to seize on, than will the rarer forms which exist in lesser numbers. Hence, the more common forms, in the race for life, will tend to beat and supplant the less common forms, for these will be more slowly modified and improved. It is the same principle which, as I believe, accounts for the common species in each country, as shown in the second chapter, presenting on an average a greater number of well-marked varieties than do the rarer species. I may illustrate what I mean by supposing three varieties of sheep to be kept, one adapted to an extensive mountainous region; a second to a comparatively narrow, hilly tract; and a third to wide plains at the base; and that the inhabitants are all trying with equal steadiness and skill to improve their stocks by selection; the chances in this case will be strongly in favour of the great holders on the mountains or on the plains improving their breeds more quickly than the small holders on the intermediate narrow, hilly tract; and consequently the improved mountain or plain breed will soon take the place of the less improved hill breed; and thus the two breeds, which originally existed in greater numbers, will come into close contact with each other, without the interposition of the supplanted, intermediate hill-variety.

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总而言之，我认为物种终究是定义相当分明的实物，在任何一个时期内，不会有无数变异着的中间环节而造成不可分解的混乱：第一，因为新变种的形成是很缓慢的，由于变异就是一个缓慢的过程，除非有利的变异碰巧发生，同时这个地区的自然系统中有位置可以让一个或更多改变的生物更好地占据，自然选择就无所作为。这样的新位置决定于气候的缓慢变化或者新生物的偶尔移入，更重要的，也许决定于某些旧生物的徐缓变异，由此产生的新类型，便和旧类型互相发生作用和反作用。所以在任何一处地方，在任何一个时候，我们应该只看到有少数物种在构造上表现出好歹持久的轻微变异；而这的确是我们看到的情形。

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To sum up, I believe that species come to be tolerably well-defined objects, and do not at any one period present an inextricable chaos of varying and intermediate links: firstly, because new varieties are very slowly formed, for variation is a very slow process, and natural selection can do nothing until favourable variations chance to occur, and until a place in the natural polity of the country can be better filled by some modification of some one or more of its inhabitants. And such new places will depend on slow changes of climate, or on the occasional immigration of new inhabitants, and, probably, in a still more important degree, on some of the old inhabitants becoming slowly modified, with the new forms thus produced and the old ones acting and reacting on each other. So that, in any one region and at any one time, we ought only to see a few species presenting slight modifications of structure in some degree permanent; and this assuredly we do see.

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第二，现在连续的地域，在过去不久的时期一定常常是隔离的部分，那里可能有许多类型，特别属于每次生育须进行交配和漫游甚广的那些纲，已经分别变得十分不同，足以列为代表物种。在此，若干代表物种和它们的共同祖先之间的中间变种，先前在这个地区的各个隔离部分内一定存在过，但是这些环节在自然选择的过程中都已淘汰灭绝，所以现今就看不到活体存在了。

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Secondly, areas now continuous must often have existed within the recent period in isolated portions, in which many forms, more especially amongst the classes which unite for each birth and wander much, may have separately been rendered sufficiently distinct to rank as representative species. In this case, intermediate varieties between the several representative species and their common parent, must formerly have existed in each broken portion of the land, but these links will have been supplanted and exterminated during the process of natural selection, so that they will no longer exist in a living state.

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第三，如有两个以上的变种在一个严密连续地域的不同部分形成，那很可能中间地带起先有中间变种形成，但是一般存在的时间不长。因为中间变种由于已经说过的理由（即由于我们所知道的亲缘密切的物种或代表物种的实际分布情形，以及公认的变种的实际分布情形），生存在中间地带的个体数量要比所连接的变种少。单从这种原因来看，中间变种就难免偶然灭绝；在通过自然选择进一步变异的过程中，它们几乎一定要被所连接的类型所压倒淘汰；因为这些类型的个体数量多，整体上有更多的变异，这样便能通过自然选择得到进一步的改进，而进一步扩大优势。

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Thirdly, when two or more varieties have been formed in different portions of a strictly continuous area, intermediate varieties will, it is probable, at first have been formed in the intermediate zones, but they will generally have had a short duration. For these intermediate varieties will, from reasons already assigned (namely from what we know of the actual distribution of closely allied or representative species, and likewise of acknowledged varieties), exist in the intermediate zones in lesser numbers than the varieties which they tend to connect. From this cause alone the intermediate varieties will be liable to accidental extermination; and during the process of further modification through natural selection, they will almost certainly be beaten and supplanted by the forms which they connect; for these from existing in greater numbers will, in the aggregate, present more variation, and thus be further improved through natural selection and gain further advantages.

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最后，不是看任何一个时期，而是看所有时期，如果我的学说正确，那无数中间变种肯定存在过，而把同群的全部物种密切连接起来；但是正如屡次说过的，自然选择这个过程，常常倾向于使亲类型和中间环节灭绝。结果，它们曾经存在的证明只能见于化石的遗物中，而这些化石的保存，如以后的一章里所要指出的，是极不完全而且间断的记载。

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Lastly, looking not to any one time, but to all time, if my theory be true, numberless intermediate varieties, linking most closely all the species of the same group together, must assuredly have existed; but the very process of natural selection constantly tends, as has been so often remarked, to exterminate the parent forms and the intermediate links. Consequently evidence of their former existence could be found only amongst fossil remains, which are preserved, as we shall in a future chapter attempt to show, in an extremely imperfect and intermittent record.

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论具有特殊习性和构造的生物之起源和过渡。——反对我的意见的人曾经问道：比方说，陆栖食肉动物怎样能够转变成具有水栖习性的食肉动物？在过渡状态中怎么能生存？不难阐明，在同一个群中现今有许多食肉动物呈现着从严格的陆栖习性到水栖习性之间密切连接的中间各级；并且由于各自为求生而斗争，显然其习性很好适应于其在自然界所处的位置。试看北美洲的水貂（Mustela vison），脚有蹼，毛皮、短腿以及尾的形状都像水獭。在夏季这种动物潜水捕鱼为食，但在漫长的冬季离开冰冻的水，像鸡貂（polecats）一样，捕食家鼠和陆栖动物。如果用另一个例子来问：食虫的四足兽怎样能够转变成能飞的蝙蝠？这个问题要难得多，我将哑口无言。然而我想，这种难点无足轻重。

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On the origin and transitions of organic beings with peculiar habits and structure.—It has been asked by the opponents of such views as I hold, how, for instance, a land carnivorous animal could have been converted into one with aquatic habits; for how could the animal in its transitional state have subsisted? It would be easy to show that within the same group carnivorous animals exist having every intermediate grade between truly aquatic and strictly terrestrial habits; and as each exists by a struggle for life, it is clear that each is well adapted in its habits to its place in nature. Look at the Mustela vison of North America, which has webbed feet and which resembles an otter in its fur, short legs, and form of tail; during summer this animal dives for and preys on fish, but during the long winter it leaves the frozen waters, and preys like other polecats on mice and land animals. If a different case had been taken, and it had been asked how an insectivorous quadruped could possibly have been converted into a flying bat, the question would have been far more difficult, and I could have given no answer. Yet I think such difficulties have very little weight.

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在这里，正如在其他场合，我处于严重不利的局面，因为从我搜集的许多惊人事例里，我只能举出一两个，来说明同属密切亲缘物种的过渡习性和构造，以及同一物种中无论恒久或暂时的多种习性。依我看，像蝙蝠这种特殊的情况，非把过渡状态的个案列成一张长表，就不足以减少其中的困难。

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Here, as on other occasions, I lie under a heavy disadvantage, for out of the many striking cases which I have collected, I can give only one or two instances of transitional habits and structures in closely allied species of the same genus; and of diversified habits, either constant or occasional, in the same species. And it seems to me that nothing less than a long list of such cases is sufficient to lessen the difficulty in any particular case like that of the bat.

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看一看松鼠科，这里的分级可谓细腻。从有的种类开始，其尾巴仅仅稍微扁平，还有一些种类，如理查森（J. Richardson）爵士所论述过的，其身体后部相当宽阔，两胁的皮膜相当丰满，直到所谓飞鼠；飞鼠的四肢甚至尾巴的基部，都由广阔的皮膜联结在一起，作用就像降落伞，可以在空中从这树滑翔到那树，距离之远实在惊人。不能怀疑，每一种构造对于每一种松鼠在其栖息的地区都各有用处，可以逃避食肉鸟兽，可以较快地采集食物，或者，有理由相信，可以减少偶然跌落的危险。然而，不能从这一事实就得出结论，每一种松鼠的构造在一切自然条件下都是所能想象的最佳构造。假设气候和植被变化了，假设与它竞争的其他啮齿类或新的食肉动物迁移进来了，旧有的食肉动物变异了，如此类推，会使我们相信，至少有些松鼠要减少数量或者灭绝，除非它们的构造也能相应变异改进，所以，特别是在变化着的生活条件下，那些肋旁皮膜越来越丰满的个体将继续保存下来，我看是不难的，它的每一变异都是有用的，都会传衍下去，这种自然选择过程的累积效果，终于会有一种完美的所谓飞鼠产生出来了。

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Look at the family of squirrels; here we have the finest gradation from animals with their tails only slightly flattened, and from others, as Sir J. Richardson has remarked, with the posterior part of their bodies rather wide and with the skin on their flanks rather full, to the so-called flying squirrels; and flying squirrels have their limbs and even the base of the tail united by a broad expanse of skin, which serves as a parachute and allows them to glide through the air to an astonishing distance from tree to tree. We cannot doubt that each structure is of use to each kind of squirrel in its own country, by enabling it to escape birds or beasts of prey, or to collect food more quickly, or, as there is reason to believe, by lessening the danger from occasional falls. But it does not follow from this fact that the structure of each squirrel is the best that it is possible to conceive under all natural conditions. Let the climate and vegetation change, let other competing rodents or new beasts of prey immigrate, or old ones become modified, and all analogy would lead us to believe that some at least of the squirrels would decrease in numbers or become exterminated, unless they also became modified and improved in structure in a corresponding manner. Therefore, I can see no difficulty, more especially under changing conditions of life, in the continued preservation of individuals with fuller and fuller flank-membranes, each modification being useful, each being propagated, until by the accumulated effects of this process of natural selection, a perfect so-called flying squirrel was produced.

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现在看一看猫猴类（Galeopithecus）飞狐猴，先前曾错放在蝙蝠类中。它那肋旁极阔的皮膜，从额角起一直延伸到尾巴，把生着长指的四肢也包含在内了，皮膜还生有伸张肌。虽然还没有适于空中滑翔构造的各级环节把猫猴类与狐猴科联结起来，然而不难设想，这样的环节先前存在过，而且各自就以滑翔不完全的飞鼠那样的步骤形成，而各级构造对于它的所有者都有用处。我觉得也没有任何不能超越的难点来进一步相信，猫猴类膜连接的指头与前臂，由于自然选择而大大增长了；这一点，就飞翔器官来讲，就可以使那动物变成蝙蝠。在某些蝙蝠里，翼膜从肩端起一直延伸到尾巴，并且把后腿都包含在内，约莫可以看到一种原来适于滑翔而不适于飞翔的构造痕迹。

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Now look at the Galeopithecus or flying lemur, which formerly was falsely ranked amongst bats. It has an extremely wide flank-membrane, stretching from the corners of the jaw to the tail, and including the limbs and the elongated fingers: the flank-membrane is, also, furnished with an extensor muscle. Although no graduated links of structure, fitted for gliding through the air, now connect the Galeopithecus with the other Lemuridae, yet I can see no difficulty in supposing that such links formerly existed, and that each had been formed by the same steps as in the case of the less perfectly gliding squirrels; and that each grade of structure had been useful to its possessor. Nor can I see any insuperable difficulty in further believing it possible that the membrane-connected fingers and fore-arm of the Galeopithecus might be greatly lengthened by natural selection; and this, as far as the organs of flight are concerned, would convert it into a bat. In bats which have the wing-membrane extended from the top of the shoulder to the tail, including the hind-legs, we perhaps see traces of an apparatus originally constructed for gliding through the air rather than for flight.

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假如有十二个属左右的鸟类灭绝了或者不为人知，谁敢冒险推测，只把翅膀用作击水的一些鸟，如大头鸭（Micropterus of Eyton）；在水中把翅膀当作鳍用，在陆上当作前脚用的一些鸟，如企鹅；把翅膀当作风帆用的一些鸟，如鸵鸟；以及翅膀在机能上没有任何用处的一些鸟，如几维鸟（Apteryx），曾经存在过呢？然而上述每一种鸟的构造，在所处的生活条件下都是有用的，因为每一种都势必在斗争中求生存，但是并不一定在一切可能条件下都是最佳的。切勿从这些话去推论，这里所讲的各级翅膀的构造（大概都由于不使用的结果），都表示鸟类实际获得完全飞翔能力所经过的步骤；但是至少表示有多少多样化过渡方式是可能的。

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If about a dozen genera of birds had become extinct or were unknown, who would have ventured to have surmised that birds might have existed which used their wings solely as flappers, like the logger-headed duck (Micropterus of Eyton); as fins in the water and front legs on the land, like the penguin; as sails, like the ostrich; and functionally for no purpose, like the Apteryx. Yet the structure of each of these birds is good for it, under the conditions of life to which it is exposed, for each has to live by a struggle; but it is not necessarily the best possible under all possible conditions. It must not be inferred from these remarks that any of the grades of wing-structure here alluded to, which perhaps may all have resulted from disuse, indicate the natural steps by which birds have acquired their perfect power of flight; but they serve, at least, to show what diversified means of transition are possible.

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看到像甲壳动物（Crustacea）和软体动物（Mollusca）这些水中呼吸动物的少数种类可以适应陆地生活；又看到飞鸟、飞兽，形形色色的飞虫，先前存在过的飞爬虫，就可以想象那些依靠鳍拍击而稍稍上升、旋转和在空中滑翔很远的飞鱼，是可以变为完全有翅膀的动物的。如果这种事情曾经发生，谁会想象到，它们在早先的过渡状态中是大洋里的居民呢？而且据我们所知，它们的初步飞翔器官是专门用来逃脱别种鱼的吞食的呢！

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Seeing that a few members of such water-breathing classes as the Crustacea and Mollusca are adapted to live on the land, and seeing that we have flying birds and mammals, flying insects of the most diversified types, and formerly had flying reptiles, it is conceivable that flying-fish, which now glide far through the air, slightly rising and turning by the aid of their fluttering fins, might have been modified into perfectly winged animals. If this had been effected, who would have ever imagined that in an early transitional state they had been inhabitants of the open ocean, and had used their incipient organs of flight exclusively, as far as we know, to escape being devoured by other fish?

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看到适应于任何特殊习性而达到高度完善的构造，如飞翔的鸟翅，我们必须记住，表现有早期过渡各级构造的动物很少会留到今日，而通过自然选择会被完善过程所淘汰。另外，我们可以断言，适于不同生活习性的构造之间的过渡状态，在早期很少大量发展，也很少具有许多从属的类型。这样，我们再回到假想的飞鱼例子，真正会飞的鱼，大概不是为了在陆上和水中用许多方法捕捉许多种类的食物，而在许多从属的类型里发展起来，直到飞翔器官达到高度完善的阶段，使得它们在生活斗争中相对于其他动物得到决定性的优势。因此，在化石状态中发现具有过渡各级构造的物种的机会总是不多的，因为个体数目少于那些构造上充分发达的物种。

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When we see any structure highly perfected for any particular habit, as the wings of a bird for flight, we should bear in mind that animals displaying early transitional grades of the structure will seldom continue to exist to the present day, for they will have been supplanted by the very process of perfection through natural selection. Furthermore, we may conclude that transitional grades between structures fitted for very different habits of life will rarely have been developed at an early period in great numbers and under many subordinate forms. Thus, to return to our imaginary illustration of the flying-fish, it does not seem probable that fishes capable of true flight would have been developed under many subordinate forms, for taking prey of many kinds in many ways, on the land and in the water, until their organs of flight had come to a high stage of perfection, so as to have given them a decided advantage over other animals in the battle for life. Hence the chance of discovering species with transitional grades of structure in a fossil condition will always be less, from their having existed in lesser numbers, than in the case of species with fully developed structures.

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现在我举两三个事例来说明同种个体间习性多样化和习性的改变。不论哪种情况下，自然选择都能轻易使动物改变构造适应其改变了的习性，或者专门适应若干习性中的一种。然而难以决定的是，究竟习性变化一般先于构造，还是构造的稍微变化引起了习性变化呢？大概两者往往同时发生的。但这些对于我们并不重要。关于习性改变的情形，只要举出现在许多英国昆虫专吃外来植物或人造食物就足够了。关于习性多样化，例子不胜枚举：我在南美洲常常观察霸鹟（Saurophagus sulphuratus）像茶隼（kestrel）似的盘旋来盘旋去，要么静静伫立在水边，然后像翠鸟（kingfisher）似的冲入水中捕鱼。在英国，有时可以看到大山雀（Parus major）几乎像旋木雀（creeper）似的攀行枝上，有时又像伯劳（shrike）似的啄小鸟的头部，把它们弄死。我好多次看见并且听到，它们像五子雀（nuthatch）似的在枝上啄食紫杉（yew）的种子。赫恩（Hearne）在北美洲看到黑熊大张其嘴在水里游泳数小时，像鲸鱼似的捕捉水中的昆虫。哪怕是如此极端的个案，如果昆虫供应源源不断，而且区域内没有更加适应环境的竞争者捷足先登，我看不难出现一个熊种族通过自然选择在构造和习性上越来越适应水族生活，嘴巴越来越大，直到产生鲸鱼一样的畸形动物。

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I will now give two or three instances of diversified and of changed habits in the individuals of the same species. When either case occurs, it would be easy for natural selection to fit the animal, by some modification of its structure, for its changed habits, or exclusively for one of its several different habits. But it is difficult to tell, and immaterial for us, whether habits generally change first and structure afterwards; or whether slight modifications of structure lead to changed habits; both probably often change almost simultaneously. Of cases of changed habits it will suffice merely to allude to that of the many British insects which now feed on exotic plants, or exclusively on artificial substances. Of diversified habits innumerable instances could be given: I have often watched a tyrant flycatcher (Saurophagus sulphuratus) in South America, hovering over one spot and then proceeding to another, like a kestrel, and at other times standing stationary on the margin of water, and then dashing like a kingfisher at a fish. In our own country the larger titmouse (Parus major) may be seen climbing branches, almost like a creeper; it often, like a shrike, kills small birds by blows on the head; and I have many times seen and heard it hammering the seeds of the yew on a branch, and thus breaking them like a nuthatch. In North America the black bear was seen by Hearne swimming for hours with widely open mouth, thus catching, like a whale, insects in the water. Even in so extreme a case as this, if the supply of insects were constant, and if better adapted competitors did not already exist in the country, I can see no difficulty in a race of bears being rendered, by natural selection, more and more aquatic in their structure and habits, with larger and larger mouths, till a creature was produced as monstrous as a whale.

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由于我们有时候看到一些个体具有不同于同种和同属异种所固有的习性，依我看，我们可以预期这些个体偶尔会产生新种，具有异常的习性，而且构造上或多或少地改变原种的模式。自然界里是有这样的事例的。啄木鸟攀登树木并从树皮裂缝里捕捉昆虫，我们能够举出比这种适应性更加动人的例子吗？然而北美洲有些啄木鸟主要以果实为食，另有一些啄木鸟却生着长翅飞行捉捕昆虫。拉普拉塔平原没有生长一株树，那里有一种啄木鸟，在每一个基本体制上，甚至在羽色、粗糙的音调、波动式的飞翔，清清楚楚地告诉我其与英国普通啄木鸟的密切血缘关系；但是这种啄木鸟从来不爬树！

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As we sometimes see individuals of a species following habits widely different from those both of their own species and of the other species of the same genus, we might expect, on my theory, that such individuals would occasionally have given rise to new species, having anomalous habits, and with their structure either slightly or considerably modified from that of their proper type. And such instances do occur in nature. Can a more striking instance of adaptation be given than that of a woodpecker for climbing trees and for seizing insects in the chinks of the bark? Yet in North America there are woodpeckers which feed largely on fruit, and others with elongated wings which chase insects on the wing; and on the plains of La Plata, where not a tree grows, there is a woodpecker, which in every essential part of its organisation, even in its colouring, in the harsh tone of its voice, and undulatory flight, told me plainly of its close blood-relationship to our common species; yet it is a woodpecker which never climbs a tree!

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海燕（petrels）是最具空中性和海洋性的鸟，但是在恬静的火地海峡间有一种名叫水雉鸟（Puffinuria berardi）的，在一般习性上，在惊人的潜水力上，在游泳姿态和被迫起飞时的飞翔姿态上，任何人都会把它误为海雀（auk）或（grebe）的；尽管如此，它在本质上还是一种海燕，只是体制的许多部分已经起了深刻的变异。关于水鸫（water-ouzel），最敏锐的观察者根据尸体检验，也决不会想象到它有半水栖的习性；然而这种陆栖鸫科鸟的异数却以潜水为生——水中使用翅膀，两脚抓握石子。

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Petrels are the most a?rial and oceanic of birds, yet in the quiet Sounds of Tierra del Fuego, the Puffinuria berardi, in its general habits, in its astonishing power of diving, its manner of swimming, and of flying when unwillingly it takes flight, would be mistaken by any one for an auk or grebe; nevertheless, it is essentially a petrel, but with many parts of its organisation profoundly modified. On the other hand, the acutest observer by examining the dead body of the water-ouzel would never have suspected its sub-aquatic habits; yet this anomalous member of the strictly terrestrial thrush family wholly subsists by diving,—grasping the stones with its feet and using its wings under water.

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有些人相信各种生物创造出来就像今日所看到的那样，他们遇到一种动物的习性与构造不相一致时，一定会大惊小怪。鹅鸭蹼脚的形成是为了游泳，还有什么更为明显的呢？然而产于高地的鹅，虽然生着蹼脚，却很少走近水边，除却奥杜邦（Audubon）外，没有人看见过四趾都有蹼的军舰鸟（frigate-bird）降落在海面上的。另一方面，和骨顶鸡（coots）都是显著的水栖鸟，但趾仅在边缘上生着膜。涉禽类（Grallatores）无膜长趾的形成，是为了便于在沼泽地和浮草上行走，还有更为明显的吗？可是美洲骨顶鸡（water-hen）几乎和骨顶鸡一样是水栖性的，而秧鸡（landrail）几乎和鹌鹑（quail）、鹧鸪（partridge）一样是陆栖性的。这些例子，可以举一反三，都是习性已经变化而构造并不相应变化。高地鹅的蹼脚在机能上可以说已经变得几乎是残迹了，虽然构造上并非如此。军舰鸟趾间深凹的膜，表明它的构造已开始变化了。

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He who believes that each being has been created as we now see it, must occasionally have felt surprise when he has met with an animal having habits and structure not at all in agreement. What can be plainer than that the webbed feet of ducks and geese are formed for swimming? yet there are upland geese with webbed feet which rarely or never go near the water; and no one except Audubon has seen the frigate-bird, which has all its four toes webbed, alight on the surface of the sea. On the other hand, grebes and coots are eminently aquatic, although their toes are only bordered by membrane. What seems plainer than that the long toes of grallatores are formed for walking over swamps and floating plants, yet the water-hen is nearly as aquatic as the coot; and the landrail nearly as terrestrial as the quail or partridge. In such cases, and many others could be given, habits have changed without a corresponding change of structure. The webbed feet of the upland goose may be said to have become rudimentary in function, though not in structure. In the frigate-bird, the deeply-scooped membrane between the toes shows that structure has begun to change.

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相信分别而无数次生物创造行为的人会说，这些例子里，造物主喜欢使一种模式的生物去代替别种模式的生物；但在我看来这只是巧言重复罢了。相信生存斗争和自然选择原理的人，则会承认各种生物都不断在努力增加个体数目，而任何生物无论在习性或构造上只要发生很小的变异，从而较同一地方的别种生物占便宜，就能攫取该生物的位置，不管与自己原来的位置有多大的不同。这样，也就不会感到奇怪了：具有蹼脚的鹅和军舰鸟生活于干燥的陆地，很少降落在水面上；具有长趾的秧鸡生活于草地、沼泽地上；啄木鸟生长在几乎没有树木的地方；鸫潜水，而海燕具有海雀的习性。

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He who believes in separate and innumerable acts of creation will say, that in these cases it has pleased the Creator to cause a being of one type to take the place of one of another type; but this seems to me only restating the fact in dignified language. He who believes in the struggle for existence and in the principle of natural selection, will acknowledge that every organic being is constantly endeavouring to increase in numbers; and that if any one being vary ever so little, either in habits or structure, and thus gain an advantage over some other inhabitant of the country, it will seize on the place of that inhabitant, however different it may be from its own place. Hence it will cause him no surprise that there should be geese and frigate-birds with webbed feet, either living on the dry land or most rarely alighting on the water; that there should be long-toed corncrakes living in meadows instead of in swamps; that there should be woodpeckers where not a tree grows; that there should be diving thrushes, and petrels with the habits of auks.

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极端完善的和复杂的器官。——眼睛具有不能模仿的装置，可以对不同距离调节其焦点，接纳不同的光量，校正像差、色差。我坦承，设想眼睛能由自然选择而形成，好像是荒谬透顶。可是理性告诉我，若能明示从简单而不完全的眼睛到复杂而完全的眼睛之间有众多级差存在，并且每级对于它的所有者都有用处；若眼睛果然有细微变异，并且变异得到遗传，而这肯定是事实；若这些变异对于处在变化着的生活条件下的任何动物是有用的；那么，相信完善而复杂的眼睛能够由自然选择而形成的这个难点就不能当真，虽然在我们想象中这是难以克服的。神经怎样对光有感觉，正如生命本身是怎样起源的一样，不是我们研究的范围。但我可以指出，若干事实令我猜测，任何敏感的神经都能够变得感光，同时感觉到发出声音的那些空气的粗糙震荡。

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Organs of extreme perfection and complication.—To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree. Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real. How a nerve comes to be sensitive to light, hardly concerns us more than how life itself first originated; but I may remark that several facts make me suspect that any sensitive nerve may be rendered sensitive to light, and likewise to those coarser vibrations of the air which produce sound.

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探求任何物种的器官得以完善的分级，应当专门观察它的直系祖先；但这几乎不可能，于是便不得不每次去观察同群的物种，即观察共同始祖类型的旁系后代，以便看出有哪些分级是可能的，也许还有机会看出早期遗传下来的不改变或小改变的某些分级。在现存的脊椎动物里，我们仅找到极少量的眼睛构造分级，从化石物种上也了解不到什么。在脊椎动物大纲内，也许得深入地层，到达已知最低的化石层，才能发现那些眼睛完善的早期阶段。

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In looking for the gradations by which an organ in any species has been perfected, we ought to look exclusively to its lineal ancestors; but this is scarcely ever possible, and we are forced in each case to look to species of the same group, that is to the collateral descendants from the same original parent-form, in order to see what gradations are possible, and for the chance of some gradations having been transmitted from the earlier stages of descent, in an unaltered or little altered condition. Amongst existing Vertebrata, we find but a small amount of gradation in the structure of the eye, and from fossil species we can learn nothing on this head. In this great class we should probably have to descend far beneath the lowest known fossiliferous stratum to discover the earlier stages, by which the eye has been perfected.

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在关节动物（Articulata）这一大纲里，起初是单纯色素层包围着的视神经，没有任何视觉机制。从这个低级阶段，可以证明存在着大量构造分级，以两条根本不同的线路分叉，直到比较完善的高级阶段。例如，某些甲壳纲具有双角膜，内角膜分成若干眼面，其中都有透镜形状的隆起。其他甲壳纲的透明视锥包围着色素，其正常行为仅仅是排除测光线锥，上端呈凸面，必须做会聚动作，而下端似乎有一个不完善的玻璃体。这里的事实陈述实在过于简短不全，却表明了现存甲壳纲眼睛存在非常多样化的分级。考虑到现存动物相对于灭绝动物来说数量极少，我看（相对于许多其他构造来说）不会特别难以相信，自然选择已经把区区色素层包围着的、透明膜遮盖着的简单视神经装置，变成了关节动物大纲里任何动物都具有的完善视觉器官了。

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In the Articulata we can commence a series with an optic nerve merely coated with pigment, and without any other mechanism; and from this low stage, numerous gradations of structure, branching off in two fundamentally different lines, can be shown to exist, until we reach a moderately high stage of perfection. In certain crustaceans, for instance, there is a double cornea, the inner one divided into facets, within each of which there is a lens shaped swelling. In other crustaceans the transparent cones which are coated by pigment, and which properly act only by excluding lateral pencils of light, are convex at their upper ends and must act by convergence; and at their lower ends there seems to be an imperfect vitreous substance. With these facts, here far too briefly and imperfectly given, which show that there is much graduated diversity in the eyes of living crustaceans, and bearing in mind how small the number of living animals is in proportion to those which have become extinct, I can see no very great difficulty (not more than in the case of many other structures) in believing that natural selection has converted the simple apparatus of an optic nerve merely coated with pigment and invested by transparent membrane, into an optical instrument as perfect as is possessed by any member of the great Articulate class.

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已经走到此处的人，如果读完本书之后，发现其中的大量事实别法无解，通过遗传学说却得到了解释，就应当进一步勇往直前，承认连鹰眼那样完善的构造也可能是自然选择形成的，虽然还并不知道过渡分级。理性应该战胜妄想；但我痛感困难之大，若有人不愿把自然选择原理扩展到这种惊人的程度，我并不奇怪。

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He who will go thus far, if he find on finishing this treatise that large bodies of facts, otherwise inexplicable, can be explained by the theory of descent, ought not to hesitate to go further, and to admit that a structure even as perfect as the eye of an eagle might be formed by natural selection, although in this case he does not know any of the transitional grades. His reason ought to conquer his imagination; though I have felt the difficulty far too keenly to be surprised at any degree of hesitation in extending the principle of natural selection to such startling lengths.

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不把眼睛比作望远镜简直不可能。我们知道望远镜是由人类的最高智者经过锲而不舍的努力而完善的，自然会推论眼睛也是通过差不多的过程而形成的。但这种推论难道不自以为是吗？我们有权去假定造物主是以人类那样的智力来工作的吗？如果必须把眼睛比作光学器具，就应当想象，有厚层的透明组织，底下有感光的神经，然后假定这一厚层内各部分缓慢而持续地改变密度，以便分离成不同密度和厚度的各层，彼此距离各不相同，各层的表面也慢慢地改变着形状。进而必须假定有一种力量，时刻密切注意着各透明层的每个轻微的偶然改变；并且根据变化的环境，仔细选择无论以任何方式或任何程度产生较明晰影像的每一个变异。必须假定，该器官的每一种新状态，都是成百万地倍增着；每种状态要一直保存到更好的状态产生出来，然后旧的状态灰飞烟灭。在生物体里，变异会引起一些轻微的改变，生殖作用会使这些改变几乎无限地倍增着，而自然选择以准确的技巧挑选每一次的改进。让这种过程成百万年地进行着；每年作用于成百万的多种类个体；难道我们不相信，这种活的光学器具会比玻璃器具制造得更好，正如造物主的工作比人做得更好吗？

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It is scarcely possible to avoid comparing the eye to a telescope. We know that this instrument has been perfected by the long-continued efforts of the highest human intellects; and we naturally infer that the eye has been formed by a somewhat analogous process. But may not this inference be presumptuous? Have we any right to assume that the Creator works by intellectual powers like those of man? If we must compare the eye to an optical instrument, we ought in imagination to take a thick layer of transparent tissue, with a nerve sensitive to light beneath, and then suppose every part of this layer to be continually changing slowly in density, so as to separate into layers of different densities and thicknesses, placed at different distances from each other, and with the surfaces of each layer slowly changing in form. Further we must suppose that there is a power always intently watching each slight accidental alteration in the transparent layers; and carefully selecting each alteration which, under varied circumstances, may in any way, or in any degree, tend to produce a distincter image. We must suppose each new state of the instrument to be multiplied by the million; and each to be preserved till a better be produced, and then the old ones to be destroyed. In living bodies, variation will cause the slight alterations, generation will multiply them almost infinitely, and natural selection will pick out with unerring skill each improvement. Let this process go on for millions on millions of years; and during each year on millions of individuals of many kinds; and may we not believe that a living optical instrument might thus be formed as superior to one of glass, as the works of the Creator are to those of man?

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若能证明有任何复杂器官不可能经过无数的、连续的、轻微的变异而形成，我的理论就要完全破产。但是我没有发现这种情形。无疑有许多器官，我们不知道其过渡诸级，考虑到那些孤立的物种就更加如此，因为根据我的理论，周围的类型已大都灭绝了。还有，考虑到一个大纲内所有成员共有的一种器官，想必是遥远的时代里形成的，此后，本纲内一切成员才发展起来，为要找寻那器官早先经过的过渡诸级，我们必须观察极古的始祖类型，可是这些类型早已灭绝了。

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If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find out no such case. No doubt many organs exist of which we do not know the transitional grades, more especially if we look to much-isolated species, round which, according to my theory, there has been much extinction. Or again, if we look to an organ common to all the members of a large class, for in this latter case the organ must have been first formed at an extremely remote period, since which all the many members of the class have been developed; and in order to discover the early transitional grades through which the organ has passed, we should have to look to very ancient ancestral forms, long since become extinct.

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我们必须极端慎言一种器官不可能通过某种过渡级而形成。低等动物里，可以举出大量例子来说明同样的器官同时能够进行全然不同的机能；如蜻蜓的幼虫和泥鳅（Cobites），消化管兼营呼吸、消化和排泄的机能。再如水螅（Hydra）可以把身体的内部翻出来，然后外层就营消化，而胃部就营呼吸了。此时，如果可以得到任何利益的话，自然选择可以轻易使本来营两种机能的部分或器官专营一种机能，于是以不知不觉的步骤，器官的性质就整体改变了。两种不同的器官，有时候同时在同一个体里营相同的机能；举一个例子——鱼类用鳃呼吸溶解在水中的空气，同时用鳔呼吸游离的空气，鳔被富有血管的隔膜分开，并有鳔管（ductus pneumaticus）供给它空气。此时，两种器官当中的一个可轻易地改变和完善，以单独担当全部的工作，在变异的过程中，可受到另一种器官的帮助；于是另一种器官可能为着完全不同的另一目的而改变，或者可能被消灭掉。

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We should be extremely cautious in concluding that an organ could not have been formed by transitional gradations of some kind. Numerous cases could be given amongst the lower animals of the same organ performing at the same time wholly distinct functions; thus the alimentary canal respires, digests, and excretes in the larva of the dragon-fly and in the fish Cobites. In the Hydra, the animal may be turned inside out, and the exterior surface will then digest and the stomach respire. In such cases natural selection might easily specialise, if any advantage were thus gained, a part or organ, which had performed two functions, for one function alone, and thus wholly change its nature by insensible steps. Two distinct organs sometimes perform simultaneously the same function in the same individual; to give one instance, there are fish with gills or branchiae that breathe the air dissolved in the water, at the same time that they breathe free air in their swimbladders, this latter organ having a ductus pneumaticus for its supply, and being divided by highly vascular partitions. In these cases, one of the two organs might with ease be modified and perfected so as to perform all the work by itself, being aided during the process of modification by the other organ; and then this other organ might be modified for some other and quite distinct purpose, or be quite obliterated.

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鱼鳔是一个好例证，明确地向我们阐明了一个重要的事实：本来为了一种目的——漂浮而构成的器官，可转变成极其不同目的——呼吸器官。在某些鱼类里，鳔又为听觉器官的一种补助器，或者说听觉器官的一部分已经充当鳔的补充器，我不知道哪种观点现在占上风。所有生理学者都承认鳔在位置和构造上与高等脊椎动物的肺是同源的或是“理想地相似”：因此，似乎可以轻易认为，自然选择实际上已经把鳔变成了肺，即专营呼吸的器官。

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The illustration of the swimbladder in fishes is a good one, because it shows us clearly the highly important fact that an organ originally constructed for one purpose, namely flotation, may be converted into one for a wholly different purpose, namely respiration. The swimbladder has, also, been worked in as an accessory to the auditory organs of certain fish, or, for I do not know which view is now generally held, a part of the auditory apparatus has been worked in as a complement to the swimbladder. All physiologists admit that the swimbladder is homologous, or “ideally similar,” in position and structure with the lungs of the higher vertebrate animals: hence there seems to me to be no great difficulty in believing that natural selection has actually converted a swimbladder into a lung, or organ used exclusively for respiration.

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我不怀疑，一切具有真肺的脊椎动物是从具有漂浮器即鳔的古代未知原始型一代一代传下来的。这样，正如我根据欧文教授关于这些器官的有趣描述推论出来的，就可以理解一个奇怪的现象，我们咽下去的每一点食物和饮料都必须经过气管上的小孔，虽然有一种美妙的装置可以使声门紧闭，但还有落入肺部的危险。高等脊椎动物已经完全失去了鳃——但在胚胎里，颈两旁的裂缝和弯弓形的动脉仍然标志着鳃的先前位置。不过可以想象，现今完全失掉的鳃，大概被自然选择逐渐利用于某一不同的目的；同样，根据某些学者的观点，环节动物（Annelids）的鳃和背鳞，与昆虫的翅膀和鞘翅是同源的；所以，古时候一度用作呼吸的器官，实际上非常可能已转变成飞翔器官了。

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I can, indeed, hardly doubt that all vertebrate animals having true lungs have descended by ordinary generation from an ancient prototype, of which we know nothing, furnished with a floating apparatus or swimbladder. We can thus, as I infer from Professor Owen’s interesting description of these parts, understand the strange fact that every particle of food and drink which we swallow has to pass over the orifice of the trachea, with some risk of falling into the lungs, notwithstanding the beautiful contrivance by which the glottis is closed. In the higher Vertebrata the branchiae have wholly disappeared— the slits on the sides of the neck and the loop-like course of the arteries still marking in the embryo their former position. But it is conceivable that the now utterly lost branchiae might have been gradually worked in by natural selection for some quite distinct purpose: in the same manner as, on the view entertained by some naturalists that the branchiae and dorsal scales of Annelids are homologous with the wings and wing-covers of insects, it is probable that organs which at a very ancient period served for respiration have been actually converted into organs of flight.

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考察器官的过渡时必须记住一种机能有转变成另一种机能的可能性，所以我要再举一个例子。有柄蔓足类有两个很小的皮折，我把它叫作保卵系带，用分泌黏液的方法把卵维系在一起，直到卵在袋中孵化。这种蔓足类没有鳃，全身表皮和卵袋表皮以及小保卵系带都营呼吸。藤壶科即无柄蔓足类则不然，没有保卵系带，卵松散地置于袋底，外面包以紧闭的壳；却生有巨大的褶皱鳃。我想，现在没有人会争议，这一科里的保卵系带与别科里的鳃是严格同源的；实际上是彼此逐渐转化的。所以，毋庸怀疑，原来作为系带的同时也轻度帮助呼吸作用的那两个小皮折，已经通过自然选择，仅仅由于尺寸增大和黏液腺的消失，就转变成鳃了。如果一切有柄蔓足类都已灭绝，因其所遭到的灭绝远较无柄蔓足类为甚，谁能想到无柄蔓足类里的鳃原本是用来防止卵被冲出袋外的器官呢？

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In considering transitions of organs, it is so important to bear in mind the probability of conversion from one function to another, that I will give one more instance. Pedunculated cirripedes have two minute folds of skin, called by me the ovigerous frena, which serve, through the means of a sticky secretion, to retain the eggs until they are hatched within the sack. These cirripedes have no branchiae, the whole surface of the body and sack, including the small frena, serving for respiration. The Balanidae or sessile cirripedes, on the other hand, have no ovigerous frena, the eggs lying loose at the bottom of the sack, in the well-enclosed shell; but they have large folded branchiae. Now I think no one will dispute that the ovigerous frena in the one family are strictly homologous with the branchiae of the other family; indeed, they graduate into each other. Therefore I do not doubt that little folds of skin, which originally served as ovigerous frena, but which, likewise, very slightly aided the act of respiration, have been gradually converted by natural selection into branchiae, simply through an increase in their size and the obliteration of their adhesive glands. If all pedunculated cirripedes had become extinct, and they have already suffered far more extinction than have sessile cirripedes, who would ever have imagined that the branchiae in this latter family had originally existed as organs for preventing the ova from being washed out of the sack?

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虽然我们必须极端慎言任何器官不可能由连续的、过渡的分级所产生，可是无疑还有严重的难点。有些难点容后面著书讨论。

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Although we must be extremely cautious in concluding that any organ could not possibly have been produced by successive transitional gradations, yet, undoubtedly, grave cases of difficulty occur, some of which will be discussed in my future work.

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最大的难点之一是中性昆虫，其构造常与雄虫和能育的雌虫大有不同；这个个案将在下章讨论。鱼的发电器官是另一种特别难解的个案；无法想象这等奇异的器官是经过什么步骤产生的。但欧文等人说得对，这些器官和普通的肌肉之间，在内部构造上是密切类似的。最近有人证明，鳐（Ray）有一个器官密切类似于发电装置，但按照玛得希（Matteuchi）的观察，并不放电。所以我们必须承认，自己实在是无知得很，无权主张任何的过渡都不可能有。

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One of the gravest is that of neuter insects, which are often very differently constructed from either the males or fertile females; but this case will be treated of in the next chapter. The electric organs of fishes offer another case of special difficulty; it is impossible to conceive by what steps these wondrous organs have been produced; but, as Owen and others have remarked, their intimate structure closely resembles that of common muscle; and as it has lately been shown that Rays have an organ closely analogous to the electric apparatus, and yet do not, as Matteuchi asserts, discharge any electricity, we must own that we are far too ignorant to argue that no transition of any kind is possible.

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发电器官是另一种更大的难点；因为只见于约十二种鱼类的身上，其中有几个种类在亲缘关系上是相距很远的。如果同样的器官见于同一纲中的若干成员，特别是这些成员具有很不相同的生活习性时，一般可以将其存在归因于共同祖先的遗传，把某些成员不具有这器官归因于通过不使用或自然选择而招致的丧失。但假如发电器官是从这样规定的唯一古代祖先遗传下来的，就可以期望一切电鱼彼此都有特殊的亲缘关系。地质学也完全不能令人相信大多数鱼类先前有过发电器官，而变异了的后代大都已经将其失掉。属于不同科目的几种昆虫里发现的发光器官，是相等的难点。还有其他个案，例如在植物里，花粉块生在端头具有黏液腺的柄上，这种很奇妙的装置，在红门兰属（Orchis）和马利筋属（Asclepias）上是一样的，但它们在显花植物中几乎是相距最远的属。在不同物种呈现看起来相同的异常器官的所有这些个案中，应该指出，尽管器官的一般外表和机能一模一样，但一般能探测到根本性的差别。我倾向于认为，就像两个人有时候会独立地得到同一个发明一样，自然选择为了各生物的利益而工作着，利用着相似的变异，而在两个生物里，有时候以相似方式改变了两个部分，所以其共同构造并不能归因于共同祖先的遗传。

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The electric organs offer another and even more serious difficulty; for they occur in only about a dozen fishes, of which several are widely remote in their affinities. Generally when the same organ appears in several members of the same class, especially if in members having very different habits of life, we may attribute its presence to inheritance from a common ancestor; and its absence in some of the members to its loss through disuse or natural selection. But if the electric organs had been inherited from one ancient progenitor thus provided, we might have expected that all electric fishes would have been specially related to each other. Nor does geology at all lead to the belief that formerly most fishes had electric organs, which most of their modified descendants have lost. The presence of luminous organs in a few insects, belonging to different families and orders, offers a parallel case of difficulty. Other cases could be given; for instance in plants, the very curious contrivance of a mass of pollen-grains, borne on a foot-stalk with a sticky gland at the end, is the same in Orchis and Asclepias,—genera almost as remote as possible amongst flowering plants. In all these cases of two very distinct species furnished with apparently the same anomalous organ, it should be observed that, although the general appearance and function of the organ may be the same, yet some fundamental difference can generally be detected. I am inclined to believe that in nearly the same way as two men have sometimes independently hit on the very same invention, so natural selection, working for the good of each being and taking advantage of analogous variations, has sometimes modified in very nearly the same manner two parts in two organic beings, which owe but little of their structure in common to inheritance from the same ancestor.

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虽然在许多情况下，要猜测器官经过什么样的过渡形式而达到今日的状态是极其困难的，但是考虑到生存的已知类型与灭绝的未知类型相比，数量极少，我感到惊异的，倒是很难举出一个器官不是经过过渡分级而形成的。此话的正确性有博物学史那古老的格言“自然界里没有飞跃”为证。有经验的学者的著作几乎都承认这句格言；米尔恩·爱德华兹说得好，自然界在玩花样方面挥霍，却在创新方面吝啬。如果依据神创论，为什么这样呢？许多独立生物既然是分别创造以适合于自然界的一定位置，为什么它们的所有部分和器官，却这样始终如一地被逐渐分级的步骤连接在一起呢？为什么自然界不采取从构造到构造的飞跃呢？依照自然选择的学说，就能够明白自然界为什么这样；因为自然选择只是利用微细的、连续的变异而发生作用；从来不可能采取飞跃，而一定是以最短最缓慢的步骤前进。

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Although in many cases it is most difficult to conjecture by what transitions an organ could have arrived at its present state; yet, considering that the proportion of living and known forms to the extinct and unknown is very small, I have been astonished how rarely an organ can be named, towards which no transitional grade is known to lead. The truth of this remark is indeed shown by that old canon in natural history of “Natura non facit saltum.” We meet with this admission in the writings of almost every experienced naturalist; or, as Milne Edwards has well expressed it, nature is prodigal in variety, but niggard in innovation. Why, on the theory of Creation, should this be so? Why should all the parts and organs of many independent beings, each supposed to have been separately created for its proper place in nature, be so invariably linked together by graduated steps? Why should not Nature have taken a leap from structure to structure? On the theory of natural selection, we can clearly understand why she should not; for natural selection can act only by taking advantage of slight successive variations; she can never take a leap, but must advance by the shortest and slowest steps.

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表面上不重要的器官。——自然选择是通过生死存亡——让具有任何有利变异的个体生存，让具有任何不利构造变异的个体灭亡——而发生作用的，所以对于次要简单部分的起源，我有时感到很难理解，因为似乎不足以让连续变异的个体生存啊。对于完美复杂器官如眼睛的个案，这方面我有时候也感到费解，虽然这是一种很不相同的困难。

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Organs of little apparent importance.—As natural selection acts by life and death,—by the preservation of individuals with any favourable variation, and by the destruction of those with any unfavourable deviation of structure,—I have sometimes felt much difficulty in understanding the origin of simple parts, of which the importance does not seem sufficient to cause the preservation of successively varying individuals. I have sometimes felt as much difficulty, though of a very different kind, on this head, as in the case of an organ as perfect and complex as the eye.

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第一，我们对于任何一种生物的全部机构太无知，说不出什么样的轻微变异重要与否。上一章举出过微细性状的一些事例，如果实上的茸毛，果肉的颜色，决定了昆虫是否来攻击，或与体质的差异相关，确实会承受自然选择的作用。长颈鹿的尾巴，宛如人造的蝇拂；说它适于现在的用途是经过连续的微细变异，每次变异都更适合驱蝇那样的琐事，初看来似乎难以置信。然而哪怕这种情况下，断言之前亦应三思；我们知道，在南美洲，牛和其他动物的分布和生存绝对取决于抗拒昆虫攻击的力量：好歹只要能防这等小敌害的个体，就能扩张到新牧场，获得巨大优势。倒不是大个的四足兽真的会被苍蝇消灭（除了少数的例外），而是不断骚扰会导致其体力降低，容易得病，有饥荒来袭时无力觅食，无力逃避猛兽攻击。

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In the first place, we are much too ignorant in regard to the whole economy of any one organic being, to say what slight modifications would be of importance or not. In a former chapter I have given instances of most trifling characters, such as the down on fruit and the colour of the flesh, which, from determining the attacks of insects or from being correlated with constitutional differences, might assuredly be acted on by natural selection. The tail of the giraffe looks like an artificially constructed fly-flapper; and it seems at first incredible that this could have been adapted for its present purpose by successive slight modifications, each better and better, for so trifling an object as driving away flies; yet we should pause before being too positive even in this case, for we know that the distribution and existence of cattle and other animals in South America absolutely depends on their power of resisting the attacks of insects: so that individuals which could by any means defend themselves from these small enemies, would be able to range into new pastures and thus gain a great advantage. It is not that the larger quadrupeds are actually destroyed (except in some rare cases) by the flies, but they are incessantly harassed and their strength reduced, so that they are more subject to disease, or not so well enabled in a coming dearth to search for food, or to escape from beasts of prey.

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现在不重要的器官，也许在某些情形里，对于早期的祖先是高度重要的，器官在以前的一个时期慢慢完善了之后，仍以近乎相同的状态传递下来，但现在已经用处极少了；构造上任何实际的有害偏差，总要受到自然选择的抑制。看到尾巴在大多数水栖动物里是何等重要的运动器官，大概就可以这样去解释它在多数陆栖动物（肺或变异了的鳔揭示了它们的水栖起源）里的一般存在和多种用途。充分发达的尾巴一旦在水栖动物里形成，其后它大概可以培养各种各样的用途，如作为蝇拂，作为握持器官，或者像狗尾那样帮助转弯，虽然转弯助力想必不大，野兔没有尾巴，照样迅速调头。

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Organs now of trifling importance have probably in some cases been of high importance to an early progenitor, and, after having been slowly perfected at a former period, have been transmitted in nearly the same state, although now become of very slight use; and any actually injurious deviations in their structure will always have been checked by natural selection. Seeing how important an organ of locomotion the tail is in most aquatic animals, its general presence and use for many purposes in so many land animals, which in their lungs or modified swim-bladders betray their aquatic origin, may perhaps be thus accounted for. A well-developed tail having been formed in an aquatic animal, it might subsequently come to be worked in for all sorts of purposes, as a fly-flapper, an organ of prehension, or as an aid in turning, as with the dog, though the aid must be slight, for the hare, with hardly any tail, can double quickly enough.

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第二，我们有时很重视实际上无足轻重的性状，它们来自次等的原因，跟自然选择无关。应该记住，气候、食物等等也许对体制没有直接影响，性状复现是由于返祖法则，相关生长在改变各种构造中影响巨大，最后，性选择常常明显改变有意志动物的外在性状，让一个雄性得到与另一个雄性打斗或者吸引异性的优点。而且，构造变异主要来自上述或者其他未知原因时，起初对于物种可能并没有什么利益，此后却会被后代在新的生活条件下和新获得的习性里所利用。

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In the second place, we may sometimes attribute importance to characters which are really of very little importance, and which have originated from quite secondary causes, independently of natural selection. We should remember that climate, food, etc., probably have some little direct influence on the organisation; that characters reappear from the law of reversion; that correlation of growth will have had a most important influence in modifying various structures; and finally, that sexual selection will often have largely modified the external characters of animals having a will, to give one male an advantage in fighting with another or in charming the females. Moreover when a modification of structure has primarily arisen from the above or other unknown causes, it may at first have been of no advantage to the species, but may subsequently have been taken advantage of by the descendants of the species under new conditions of life and with newly acquired habits.

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举例说明上面最后的话。如果只有绿色的啄木鸟生存着，就不知道还有许多种黑色和杂色的啄木鸟，我敢说我们一定会以为绿色是一种美妙的适应，使这种频繁往来于树木之间的鸟类得以在敌害面前隐蔽自己；结果就会认为这是一种重要的性状，并且是通过自然选择而获得的；其实毋庸置疑这颜色出于截然不同的原因，也许是来自性选择。马来群岛有一种藤棕榈（trailing bamboo），依靠丛生在枝端的构造精致的钩，攀缘最高的树木，这种装置对于这植物无疑是极有用处的；但是我们在许多非攀缘性的树上也看到极相似的钩，所以藤棕榈的钩最初可能来自未知的生长法则，后来当该植物进一步发生变异，成为攀缘植物的时候，钩就被利用了。秃鹫（vulture）头上裸出的皮，普遍被认为是为了吞食腐败物的一种直接适应；也许是这样，也许可能是由于腐败物质的直接作用；但是当我们看到吃清洁食物的雄火鸡头皮也这样裸出时，就要慎于做任何这样的推论。幼小哺乳动物头骨上的缝被认为是帮助产出的美妙适应而改进，毫无疑问，这能使生产容易，也许这是为生产所必需的；但是，幼小的鸟类和爬行动物只要从破裂蛋壳里爬出来，头骨也有缝，所以我们可以推想这种构造的发生来自生长法则，不过高等动物把它利用在生产上罢了。

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To give a few instances to illustrate these latter remarks. If green woodpeckers alone had existed, and we did not know that there were many black and pied kinds, I dare say that we should have thought that the green colour was a beautiful adaptation to hide this tree-frequenting bird from its enemies; and consequently that it was a character of importance and might have been acquired through natural selection; as it is, I have no doubt that the colour is due to some quite distinct cause, probably to sexual selection. A trailing bamboo in the Malay Archipelago climbs the loftiest trees by the aid of exquisitely constructed hooks clustered around the ends of the branches, and this contrivance, no doubt, is of the highest service to the plant; but as we see nearly similar hooks on many trees which are not climbers, the hooks on the bamboo may have arisen from unknown laws of growth, and have been subsequently taken advantage of by the plant undergoing further modification and becoming a climber. The naked skin on the head of a vulture is generally looked at as a direct adaptation for wallowing in putridity; and so it may be, or it may possibly be due to the direct action of putrid matter; but we should be very cautious in drawing any such inference, when we see that the skin on the head of the clean-feeding male turkey is likewise naked. The sutures in the skulls of young mammals have been advanced as a beautiful adaptation for aiding parturition, and no doubt they facilitate, or may be indispensable for this act; but as sutures occur in the skulls of young birds and reptiles, which have only to escape from a broken egg, we may infer that this structure has arisen from the laws of growth, and has been taken advantage of in the parturition of the higher animals.

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对于轻微次要变异的原因，我们一无所知；考虑到各地家养动物品种间的差异——特别是在文明较低的国家里，那里还极少人工选择——就会立刻意识到这一点。某些仔细观察者相信潮湿气候会影响毛的生长，而角又与毛相关。高山品种总是与低地品种有差异；山区大概对后腿有锻炼，甚至影响骨盆的形状；于是，根据同源变异的法则，前肢和头部大概也要受到影响。还有，骨盆的形状可能因压力而影响子宫里小牛脑袋的形状。高原地区需费力呼吸，我们有理由相信，可使胸部增大；而且相关作用又有效力。各地未开化人所养育的动物还常常要为自己的生存而斗争，并且在某种程度上是暴露在自然选择作用之下的，同时体质稍微不同的个体，在不同的气候下最容易得到成功。有理由相信，体质和体色相关。观察者还说，牛对于蝇的攻击的感受性与体色相关，被某些植物毒倒的易感性也是这样；所以颜色也是这样服从自然选择的作用的。但是我们实在太无知了，无法对于变异的若干已知未知原因的相对重要性加以思辨；我这里提到它们，只在于表明，尽管一般都承认家养品种经过寻常的世代而产生，我们却不能解释它们性状差异的原因，既然如此，我们对于物种之间的微小相似差异，还不能了解其真实原因，就不必耿耿于怀了。我为了同样的目的，可以引证人种之间的差别，标记鲜明。还可以补充说明这些差别的来源，主要是通过某种性选择。但这里无法铺开浩瀚的细节，推理未免显得浅尝辄止。

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We are profoundly ignorant of the causes producing slight and unimportant variations; and we are immediately made conscious of this by reflecting on the differences in the breeds of our domesticated animals in different countries,—more especially in the less civilized countries where there has been but little artificial selection. Careful observers are convinced that a damp climate affects the growth of the hair, and that with the hair the horns are correlated. Mountain breeds always differ from lowland breeds; and a mountainous country would probably affect the hind limbs from exercising them more, and possibly even the form of the pelvis; and then by the law of homologous variation, the front limbs and even the head would probably be affected. The shape, also, of the pelvis might affect by pressure the shape of the head of the young in the womb. The laborious breathing necessary in high regions would, we have some reason to believe, increase the size of the chest; and again correlation would come into play. Animals kept by savages in different countries often have to struggle for their own subsistence, and would be exposed to a certain extent to natural selection, and individuals with slightly different constitutions would succeed best under different climates; and there is reason to believe that constitution and colour are correlated. A good observer, also, states that in cattle susceptibility to the attacks of flies is correlated with colour, as is the liability to be poisoned by certain plants; so that colour would be thus subjected to the action of natural selection. But we are far too ignorant to speculate on the relative importance of the several known and unknown laws of variation; and I have here alluded to them only to show that, if we are unable to account for the characteristic differences of our domestic breeds, which nevertheless we generally admit to have arisen through ordinary generation, we ought not to lay too much stress on our ignorance of the precise cause of the slight analogous differences between species. I might have adduced for this same purpose the differences between the races of man, which are so strongly marked; I may add that some little light can apparently be thrown on the origin of these differences, chiefly through sexual selection of a particular kind, but without here entering on copious details my reasoning would appear frivolous.

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最近有学者反对功利说所主张的构造每一细微之点的产生都是为了所有者的利益，前节的论点促使我对这种反调说几句。他们相信许多构造创造出来，是为了人类眼里的美，或仅仅为了多样化。这个说教如果正确，对我的学说就是致命的。我完全承认，有许多构造对于所有者没有直接用处。外界条件对于构造也许有一点点作用，与由此而获得的利益都不相干。相关生长无疑起了十分重要的作用，一个部分的有用变异往往引起其他部分产生没有直接用处的多样性变化。还有以前有用的性状，或者以前来自相关生长的性状，或者来自未知原因的性状，会因为返祖法则而重新出现，尽管现在已经没有用处。性选择的作用体现为吸引雌性的美，只可颇为勉强地称为有用。但是最最重要的一点理由是，各种生物的体制的主要部分都是由遗传而来的；结果，虽然每一生物确是适于它在自然界中的位置，但是有许多构造与物种的生活习性并没有直接的关系。例如，我们很难相信，高地鹅和军舰鸟的蹼脚对于它们有什么特别的用处；我们不能相信在猴子的臂内、马的前腿内、蝙蝠的翅膀内、海豹的鳍脚内，相似的骨对于这些动物有什么特别的用处。我们可以很稳妥地把这些构造归因于遗传。但是蹼脚对于高地鹅和军舰鸟的祖先无疑是有用的，正如对于现存的水栖鸟一样。所以我们可以相信，海豹的祖先并不生有鳍脚，却生有五个趾的脚，适于走或抓握；我们还可以进一步大胆相信：猴子、马和蝙蝠的四肢内的若干骨头，从共同祖先遗传而来，以前是那个祖先或者祖先的祖先们专用的，而不是供现在习性多样化的这些动物使用。因此我们可以推论，这若干骨头可能是通过自然选择获得的，过去和现在一样，受制于各种遗传、返祖、相关生长等法则。因此，所有生物的所有构造细节（给外界条件的直接作用留一些余地）可以看作为某个祖先类型所专用，或者现在为该类型的后代所专用——要么直接，要么通过复杂的生长法则间接进行。

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The foregoing remarks lead me to say a few words on the protest lately made by some naturalists, against the utilitarian doctrine that every detail of structure has been produced for the good of its possessor. They believe that very many structures have been created for beauty in the eyes of man, or for mere variety. This doctrine, if true, would be absolutely fatal to my theory. Yet I fully admit that many structures are of no direct use to their possessors. Physical conditions probably have had some little effect on structure, quite independently of any good thus gained. Correlation of growth has no doubt played a most important part, and a useful modification of one part will often have entailed on other parts diversified changes of no direct use. So again characters which formerly were useful, or which formerly had arisen from correlation of growth, or from other unknown cause, may reappear from the law of reversion, though now of no direct use. The effects of sexual selection, when displayed in beauty to charm the females, can be called useful only in rather a forced sense. But by far the most important consideration is that the chief part of the organisation of every being is simply due to inheritance; and consequently, though each being assuredly is well fitted for its place in nature, many structures now have no direct relation to the habits of life of each species. Thus, we can hardly believe that the webbed feet of the upland goose or of the frigate-bird are of special use to these birds; we cannot believe that the same bones in the arm of the monkey, in the fore leg of the horse, in the wing of the bat, and in the flipper of the seal, are of special use to these animals. We may safely attribute these structures to inheritance. But to the progenitor of the upland goose and of the frigate-bird, webbed feet no doubt were as useful as they now are to the most aquatic of existing birds. So we may believe that the progenitor of the seal had not a flipper, but a foot with five toes fitted for walking or grasping; and we may further venture to believe that the several bones in the limbs of the monkey, horse, and bat, which have been inherited from a common progenitor, were formerly of more special use to that progenitor, or its progenitors, than they now are to these animals having such widely diversified habits. Therefore we may infer that these several bones might have been acquired through natural selection, subjected formerly, as now, to the several laws of inheritance, reversion, correlation of growth, etc. Hence every detail of structure in every living creature (making some little allowance for the direct action of physical conditions) may be viewed, either as having been of special use to some ancestral form, or as being now of special use to the descendants of this form—either directly, or indirectly through the complex laws of growth.

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自然选择不可能使一个物种产生出唯独对另一个物种有利的任何变异；虽然在整个自然界中，一个物种不断地利用另一物种的构造而获益。不过，自然选择能够而且的确常常产生出直接对别种动物有害的构造，如蝮蛇的毒牙，姬蜂的产卵管能够在别种活昆虫的身体里产卵。假如能够证明，任何一个物种的构造的任何一部分全然为了另一物种的利益而形成，那就要推翻我的理论了，因为这构造是不能通过自然选择产生的。虽然博物学著作里有许多陈述提到该事，但找不到一句话看起来是有分量的。尽管响尾蛇的毒牙系用以自卫和杀害猎物，但某些作者假定它同时具有于自己不利的响器，会预先警告猎物躲避。我恨不得认为，猫准备纵跳时卷动尾端是为了使大祸临头的鼠警戒起来。但这里限于篇幅，无法详述。

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Natural selection cannot possibly produce any modification in any one species exclusively for the good of another species; though throughout nature one species incessantly takes advantage of, and profits by, the structure of another. But natural selection can and does often produce structures for the direct injury of other species, as we see in the fang of the adder, and in the ovipositor of the ichneumon, by which its eggs are deposited in the living bodies of other insects. If it could be proved that any part of the structure of any one species had been formed for the exclusive good of another species, it would annihilate my theory, for such could not have been produced through natural selection. Although many statements may be found in works on natural history to this effect, I cannot find even one which seems to me of any weight. It is admitted that the rattlesnake has a poison-fang for its own defence and for the destruction of its prey; but some authors suppose that at the same time this snake is furnished with a rattle for its own injury, namely, to warn its prey to escape. I would almost as soon believe that the cat curls the end of its tail when preparing to spring, in order to warn the doomed mouse. But I have not space here to enter on this and other such cases.

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自然选择从来不使一种生物产生损害自己的任何构造，唯有根据各种生物的利益并且为了它们的利益而起作用。正如帕利（Paley）说过的，没有一种器官的形成是为了给予它的所有者以痛苦或损害。如果公平权衡各个部分所引起的利和害，就可以看到，从整体来说，各个部分都是有利的。随着时间的推移，生活条件改变，如果任何部分变为有害的，那就要变异；否则这种生物就要灭绝，如灭绝了的大部队那样。

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Natural selection will never produce in a being anything injurious to itself, for natural selection acts solely by and for the good of each. No organ will be formed, as Paley has remarked, for the purpose of causing pain or for doing an injury to its possessor. If a fair balance be struck between the good and evil caused by each part, each will be found on the whole advantageous. After the lapse of time, under changing conditions of life, if any part comes to be injurious, it will be modified; or if it be not so, the being will become extinct, as myriads have become extinct.

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自然选择只是倾向于使每一种生物跟共栖息地、被迫进行生存斗争的别种生物一样地完善，或者稍微更加完善一些。我们可以看到，这就是自然状况下所得到的完善程度。例如，新西兰的土著生物彼此相比都是完善的，但是在欧洲引进的动植物大军压境面前，正在迅速屈服。自然选择不会产生绝对的完善，并且就我们所能判断的来说，也不总是在自然界里遇见这种高标准。据权威说，光线像差的校正，甚至在最完善的器官眼睛里，也不是完全的。如果理性促使我们热烈地赞美自然界里有无数不能模仿的装置，那么它又告诉我们说（纵然我们在两方面都易犯错），某些其他装置不那么完善。我们能够认为蜜蜂的螫针是完善的吗？对付多种敌害的时候，螫针有倒生的小锯齿无法自拔，这样，自己的内脏就被拉出，不可避免地要引起蜜蜂的死亡。

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Natural selection tends only to make each organic being as perfect as, or slightly more perfect than, the other inhabitants of the same country with which it has to struggle for existence. And we see that this is the degree of perfection attained under nature. The endemic productions of New Zealand, for instance, are perfect one compared with another; but they are now rapidly yielding before the advancing legions of plants and animals introduced from Europe. Natural selection will not produce absolute perfection, nor do we always meet, as far as we can judge, with this high standard under nature. The correction for the aberration of light is said, on high authority, not to be perfect even in that most perfect organ, the eye. If our reason leads us to admire with enthusiasm a multitude of inimitable contrivances in nature, this same reason tells us, though we may easily err on both sides, that some other contrivances are less perfect. Can we consider the sting of the wasp or of the bee as perfect, which, when used against many attacking animals, cannot be withdrawn, owing to the backward serratures, and so inevitably causes the death of the insect by tearing out its viscera?

55
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如果把蜜蜂的螫针看作在遥远的祖先里已经存在，原是穿孔用的锯齿状器具，就像这个大目里的许多成员那样，后来为了现在的目的被改变了，但没有完善，而它的毒素原本是适于产生树瘿，后来才强化，我们就大概能够理解，为什么蜜蜂一用螫针就往往引起自身死亡：如果螫针的能力总体上对于蜂群有用处，虽然可以引起少数成员的死亡，却可以满足自然选择的一切要求。如果我们赞叹许多昆虫中的雄虫依靠嗅觉的神奇能力去寻找雌虫，那么，也赞叹只为了这个目的而产生万千雄蜂，对于蜂群没有一点其他用处，终于被那些勤劳而不育的姊妹弄死吗？也许是难以赞叹的，但是应当赞叹蜂后的野蛮本能的恨，促使它在幼小的蜂后女儿们刚生出来就瞬间将其弄死，或者自己在这场战斗中死亡；因为没有疑问，这对于蜂群是有好处的；母爱或母恨（幸而后者很少），对于自然选择的不可抗拒原则来说是一视同仁。如果我们赞叹兰科植物和许多其他植物的几种巧妙装置，通过昆虫的助力来受精，那么赤松精致的花粉雾，让少数几粒能够碰巧吹到胚珠上去，我们能够认为同等完善吗？

55
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If we look at the sting of the bee, as having originally existed in a remote progenitor as a boring and serrated instrument, like that in so many members of the same great order, and which has been modified but not perfected for its present purpose, with the poison originally adapted to cause galls subsequently intensified, we can perhaps understand how it is that the use of the sting should so often cause the insect’s own death: for if on the whole the power of stinging be useful to the community, it will fulfil all the requirements of natural selection, though it may cause the death of some few members. If we admire the truly wonderful power of scent by which the males of many insects find their females, can we admire the production for this single purpose of thousands of drones, which are utterly useless to the community for any other end, and which are ultimately slaughtered by their industrious and sterile sisters? It may be difficult, but we ought to admire the savage instinctive hatred of the queen-bee, which urges her instantly to destroy the young queens her daughters as soon as born, or to perish herself in the combat; for undoubtedly this is for the good of the community; and maternal love or maternal hatred, though the latter fortunately is most rare, is all the same to the inexorable principle of natural selection. If we admire the several ingenious contrivances, by which the flowers of the orchis and of many other plants are fertilised through insect agency, can we consider as equally perfect the elaboration by our fir-trees of dense clouds of pollen, in order that a few granules may be wafted by a chance breeze on to the ovules?

56
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本章提要。——这一章讨论了可以用来反对我的理论的一些难点和异议。其中有许多是严重的；但是，我想在这里对于一些事实已经澄清说明，而依照特创论的信条，这些事实是一塌糊涂。我们已经看到，物种在任何一个时期的变异都不是无限的，也没有由无数的中间分级联系起来，部分原因是自然选择的过程总是极其缓慢的，在任何一个时期只对少数类型发生作用，部分原因是自然选择这一过程本身就意味着先驱的中间级不断淘汰灭绝。现今生存于连续地域上的亲缘密切的物种，往往在这个地域还没有连续起来、生活条件还没有从这一处不知不觉地逐渐变化到另一处的时候，就已经形成了。当两个变种在连续地域的两处形成的时候，常有适于中间地带的中间变种形成；但依照上述的理由，中间变种的个体数量通常要比所连接的两个变种少；结果，这两个变种进一步变异的过程中，由于个体数量较多，便比数量少的中间变种占有强大的优势，因此，一般就会成功地把中间变种淘汰消灭掉。

56
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Summary of Chapter.—We have in this chapter discussed some of the difficulties and objections which may be urged against my theory. Many of them are very grave; but I think that in the discussion light has been thrown on several facts, which on the theory of independent acts of creation are utterly obscure. We have seen that species at any one period are not indefinitely variable, and are not linked together by a multitude of intermediate gradations, partly because the process of natural selection will always be very slow, and will act, at any one time, only on a very few forms; and partly because the very process of natural selection almost implies the continual supplanting and extinction of preceding and intermediate gradations. Closely allied species, now living on a continuous area, must often have been formed when the area was not continuous, and when the conditions of life did not insensibly graduate away from one part to another. When two varieties are formed in two districts of a continuous area, an intermediate variety will often be formed, fitted for an intermediate zone; but from reasons assigned, the intermediate variety will usually exist in lesser numbers than the two forms which it connects; consequently the two latter, during the course of further modification, from existing in greater numbers, will have a great advantage over the less numerous intermediate variety, and will thus generally succeed in supplanting and exterminating it.

57
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我们在本章里已经看到，应该特别慎言极其不同的生活习性不能逐渐彼此转化；譬如断言蝙蝠不能通过自然选择从一种最初只在空中滑翔的动物形成。

57
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We have seen in this chapter how cautious we should be in concluding that the most different habits of life could not graduate into each other; that a bat, for instance, could not have been formed by natural selection from an animal which at first could only glide through the air.

58
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我们已经看到，一个物种在新的生活条件下可以改变习性，或者有多样化的习性，其中有些和最近同类很不相同。因此，只要记住各生物都在试图生活于任何可以生活的地方，我们就能理解脚上有蹼的高地鹅、栖居地上的啄木鸟、潜水的鸫和具有海雀习性的海燕是怎样产生的了。

58
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We have seen that a species may under new conditions of life change its habits, or have diversified habits, with some habits very unlike those of its nearest congeners. Hence we can understand, bearing in mind that each organic being is trying to live wherever it can live, how it has arisen that there are upland geese with webbed feet, ground woodpeckers, diving thrushes, and petrels with the habits of auks.

59
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像眼睛那样完善的器官，要说能够由自然选择形成，这足以使任何人震惊；但是不论何种器官，只要我们知道其一系列复杂、逐渐过渡的分级，各个对于所有者都有益处，在改变着的生活条件下，通过自然选择而达到任何可以想象的完善程度，在逻辑上并非不可能。在不知道有中间状态或过渡状态的情形里，必须极端慎言不能有这些状态曾经存在过，因为许多器官的同源和中间状态阐明了，机能上的奇异变化至少是可能的。例如，鳔显然已经转变成呼吸空气的肺了。同时进行多种不同机能的、然后变为专营一种机能的同一器官，同时进行同种机能的、一种器官受到另一种器官的帮助而完善的两种不同器官，一定常常会大大促进过渡。

59
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Although the belief that an organ so perfect as the eye could have been formed by natural selection, is more than enough to stagger any one; yet in the case of any organ, if we know of a long series of gradations in complexity, each good for its possessor, then, under changing conditions of life, there is no logical impossibility in the acquirement of any conceivable degree of perfection through natural selection. In the cases in which we know of no intermediate or transitional states, we should be very cautious in concluding that none could have existed, for the homologies of many organs and their intermediate states show that wonderful metamorphoses in function are at least possible. For instance, a swim-bladder has apparently been converted into an air-breathing lung. The same organ having performed simultaneously very different functions, and then having been specialised for one function; and two very distinct organs having performed at the same time the same function, the one having been perfected whilst aided by the other, must often have largely facilitated transitions.

60
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在大多数情形里，我们实在太无知无识了，居然主张任何部分或器官对于物种的利益极其不重要，所以其构造上的变异，不可能由自然选择缓缓累积起来。但我们满可以认为，许多变异完全是生长法则带来的，起初对物种没有任何利益，但后来被进一步变异的后代所利用。我们还可以相信，从前高度重要的部分，虽然已变得不重要，在目前状态下，已不可能由自然选择而获得，但往往还会保留着（如水栖动物的尾巴仍然保留在陆栖后代里）。自然选择的力量仅仅通过保留生存斗争中出现的有利变异而起作用。

60
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We are far too ignorant, in almost every case, to be enabled to assert that any part or organ is so unimportant for the welfare of a species, that modifications in its structure could not have been slowly accumulated by means of natural selection. But we may confidently believe that many modifications, wholly due to the laws of growth, and at first in no way advantageous to a species, have been subsequently taken advantage of by the still further modified descendants of this species. We may, also, believe that a part formerly of high importance has often been retained (as the tail of an aquatic animal by its terrestrial descendants), though it has become of such small importance that it could not, in its present state, have been acquired by natural selection,—a power which acts solely by the preservation of profitable variations in the struggle for life.

61
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自然选择不会在一个物种里产生出唯独有利于或者有害于另一个物种的任何东西；虽然能够有效地产生出对于另一物种极其有用的，甚至不可缺少的或者极其有害的部分、器官和分泌物，但是在所有情形里同时也是对它们的所有者有用的。在生物繁生的各个地方，自然选择必须主要通过生物的相互竞争而发生作用，于是，只是依照这个地方的标准产生完美，在生存战斗中产生力量。因此，一个地方，通常是较小地方的生物，常常屈服于另一个地方，通常是较大地方的生物，这一点我们有证据。在大的地方，有比较多的个体和比较多样化的类型存在，竞争比较剧烈，完善的标准也就比较高。自然选择不一定能导致绝对的完善；依照我们的有限才能来判断，绝对的完善也不是随处可见的。

61
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Natural selection will produce nothing in one species for the exclusive good or injury of another; though it may well produce parts, organs, and excretions highly useful or even indispensable, or highly injurious to another species, but in all cases at the same time useful to the owner. Natural selection in each well-stocked country, must act chiefly through the competition of the inhabitants one with another, and consequently will produce perfection, or strength in the battle for life, only according to the standard of that country. Hence the inhabitants of one country, generally the smaller one, will often yield, as we see they do yield, to the inhabitants of another and generally larger country. For in the larger country there will have existed more individuals, and more diversified forms, and the competition will have been severer, and thus the standard of perfection will have been rendered higher. Natural selection will not necessarily produce absolute perfection; nor, as far as we can judge by our limited faculties, can absolute perfection be everywhere found.

62
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依据自然选择学说，我们能明白博物学里“自然界里没有飞跃”这个老格言的充分意义。如果只看世界上的现存生物，这格言并不是严格正确的；但如果把过去的一切生物都包括在内，这格言按照我的理论必定是严格正确的。

62
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On the theory of natural selection we can clearly understand the full meaning of that old canon in natural history, “Natura non facit saltum.” This canon, if we look only to the present inhabitants of the world, is not strictly correct, but if we include all those of past times, it must by my theory be strictly true.

63
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一般公认，全部生物都是依照两大法则形成的——“模式统一”和“生存条件”。模式统一是指同纲生物与生活习性无关的构造上基本一致而言。依照我的理论，模式的统一可以用世系的统一来解释。曾被著名的居维叶所经常坚持的生存条件的说法，完全可以包括在自然选择的原理之内。因为自然选择的作用在于使各生物的变异部分现今适用于有机和无机的生存条件，或者在于使它们在过去的时代里如此去适应：在某些情况下，适应受到用或废的帮助，稍微受到外界生活条件的直接作用的影响，并且在一切场合里受制于生长变异的若干法则。事实上，生存条件法则是高级法则；因为通过遗传以前的变异，包括了模式统一法则。

63
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It is generally acknowledged that all organic beings have been formed on two great laws—Unity of Type, and the Conditions of Existence. By unity of type is meant that fundamental agreement in structure, which we see in organic beings of the same class, and which is quite independent of their habits of life. On my theory, unity of type is explained by unity of descent. The expression of conditions of existence, so often insisted on by the illustrious Cuvier, is fully embraced by the principle of natural selection. For natural selection acts by either now adapting the varying parts of each being to its organic and inorganic conditions of life; or by having adapted them during long-past periods of time: the adaptations being aided in some cases by use and disuse, being slightly affected by the direct action of the external conditions of life, and being in all cases subjected to the several laws of growth. Hence, in fact, the law of the Conditions of Existence is the higher law; as it includes, through the inheritance of former adaptations, that of Unity of Type.

序号 英文/音标 中文解释 更多操作

descent

[dɪ’sent]

n.下降;下坡;家世;血统;侵袭;衰落;继承

modification

[ˌmɒdɪfɪ’keɪʃn]

n.修改;修正;修饰

transitional

[træn’sɪʃənl]

adj.变化的;过渡期的;过渡性的

diversify

[daɪ’vɜːsɪfaɪ]

vt.使多样化;使变化;使不同

embraceable

[ɪm’breɪsəbl]

v.拥抱;包含;包围;接受;信奉

stagger

[’stæɡə(r)]

vi.蹒跚;犹豫;动摇

wholly

[’həʊlli]

adv.完全地;全部地;一概

mathematician

[ˌmæθəmə’tɪʃn]

n.数学家

offspring

[’ɒfsprɪŋ]

n.后代;子孙;产物

whereas

[ˌweər’æz]

conj.然而;鉴于

Hybridism

[’haɪbrɪdɪzəm]

n.混和性

preservation

[ˌprezə’veɪʃn]

n.保存

exterminate

[ɪk’stɜːmɪneɪt]

vt.消灭;扑灭;根绝

embed

[ɪm’bed]

v.(使)插入;(使)嵌入;深留脑中

crust

[krʌst]

n.外壳;坚硬的外壳;面包皮

chiefly

[’tʃiːfli]

adv.主要地

inhabit

[ɪn’hæbɪt]

v.居住于;占据;栖息

sediment

[’sedɪmənt]

n.沉淀物

degradation

[ˌdeɡrə’deɪʃn]

n.降低;堕落;退化

subside

[səb’saɪd]

vi.沉没;平息;下陷

stationary

[’steɪʃənri]

adj.静止的

interlock

[ˌɪntə’lɒk]

v.连结;连锁

specimen

[’spesɪmən]

n.标本;样本

supplant

[sə’plɑːnt]

v. 取代; 排挤根除

past

[pɑːst]

a. 过去的;

confound

[kən’faʊnd]

vt.使困惑;混淆;挫败;诅咒

infer

[ɪn’fɜː(r)]

vt.推断;猜测;暗示

Geology

[dʒi’ɒlədʒi]

n.地质学;(某地区的)地质情况;地质学的著作

ascend

[ə’send]

v.上升;攀登

dredge

[dredʒ]

v.用挖泥机疏浚;把粉撒在;努力回忆;翻出

prey

[preɪ]

n.牺牲者;被掠食者，猎物

indirect

[ˌɪndə’rekt]

adj.间接的;迂回的

lessen

[’lesn]

v.减少;减轻

liable

[’laɪəbl]

a. 有(法律)责任的；有义务的;

utter

[’ʌtə(r)]

adj.完全的;全然的;绝对的

comparative

[kəm’pærətɪv]

adj.比较的;相当的

lesser

[’lesə(r)]

adj.较少的;较小的;次要的

genus

[’dʒiːnəs]

n.【生物学】属;类;种;型

numerical

[njuː’merɪkl]

adj.数字的;用数字表示的

inference

[’ɪnfərəns]

n.推理;推论;推断;结论

sooner

[’suːnə]

adv. soon的比较级

eminent

[’emɪnənt]

adj.著名的;卓越的

inroad

[’ɪnrəʊd]

n.侵袭;消耗某物;进展

mountainous

[’maʊntənəs]

adj.多山的;如山一般的

hilly

[’hɪli]

adj.多小山的;丘陵的

tract

[trækt]

n.大片土地;器官系统

holder

[’həʊldə(r)]

n.持有者;支持物;固定器

duration

[dju’reɪʃn]

n.持续时间

aggregate

[’æɡrɪɡət]

adj.合计的;总的

imperfect

[ɪm’pɜːfɪkt]

adj.不完美的;有缺点的;未完善的

intermittent

[ˌɪntə’mɪtənt]

adj.间歇的;断断续续的

aquatic

[ə’kwætɪk]

adj.水生的;水中的;水上的

subsist

[səb’sɪst]

v.供给食物;维持生活;生存;供养

terrestrial

[tə’restriəl]

adj.陆地的;陆生的;地球的

dive

[daɪv]

n.潜水;跳水

squirrel

[’skwɪrəl]

n.松鼠;松鼠皮毛

gradation

[ɡrə’deɪʃn]

n.渐变;阶段;等级;刻度;元音交替

flatten

[’flætn]

vt.使变平;打倒

flank

[flæŋk]

n.侧面;侧腹;腰窝肉

parachute

[’pærəʃuːt]

n.降落伞;缓降物;【动】翅膜

glide

[ɡlaɪd]

v.滑动;滑翔;溜走

vegetation

[ˌvedʒə’teɪʃn]

n.植物;草木

rodent

[’rəʊdnt]

n.啮齿动物

fuller

[fʊlə]

n.压槽锤;【纺织】漂洗工

propagate

[’prɒpəɡeɪt]

v.繁殖;增殖;传播;传送

stretchable

[stretʃəbl]

v.伸展;延伸;张开;夸大

elongate

[’iːlɒŋɡeɪt]

v.延长;伸长

lengthen

[’leŋθən]

v.加长;延长

extinct

[ɪk’stɪŋkt]

adj.灭绝的;熄灭的;消亡的

surmise

[sə’maɪz]

n.推测

flapper

[’flæpə(r)]

n.拍击物;(口)(20世纪20年代的)不拘传统的时髦少女

allude

[ə’luːd]

v.暗示;暗指

disuse

[dɪs’juːs]

n.废止

incipient

[ɪn’sɪpiənt]

adj.起初的;初期的

devour

[dɪ’vaʊə(r)]

v.吞食;毁灭;贪婪地阅读

imaginary

[ɪ’mædʒɪnəri]

adj.想象的;虚构的

simultaneous

[ˌsɪml’teɪniəs]

adj.同时发生的;同步的

hover

[’hɒvə(r)]

v.盘旋;徘徊;靠近(某事物)，维持在某种不确定的状态

hammer

[’hæmə(r)]

n.锤子;榔头

adaptation

[ˌædæp’teɪʃn]

n.改编;改编成的作品;适应;【心】(感官)适应，适应性变化

bark

[bɑːk]

v.(狗)吠;咆哮

petrel

[’petrəl]

n.海燕类

unwilling

[ʌn’wɪlɪŋ]

adj.不愿意的

felted

[’feltɪd]

v. 把 ... 制成毡(使 ... 粘结)

upland

[’ʌplənd]

n.高地;山地

membrane

[’membreɪn]

n.【C】薄膜;膜状物

swamp

[swɒmp]

n.沼泽;湿地;困境

Creator

[kri’eɪtə(r)]

n.创造者;【计】创建者

restate

[ˌriː’steɪt]

v.重申;重述

dignify

[’dɪɡnɪfaɪ]

vt.使高贵;使增辉;抬高…的身价;将…美其名为

alight

[ə’laɪt]

vi. 下(马、车);

thrush

[θrʌʃ]

n.画眉;【动】鸫科;【医】鹅口疮

complication

[ˌkɒmplɪ’keɪʃn]

n.复杂;并发症;纠纷

correction

[kə’rekʃn]

n.订正;改正

spherical

[’sferɪkl]

adj.球的;球面的;球状的

chromatic

[krə’mætɪk]

a. 彩色的，颜色的;

coarse

[kɔːs]

adj.粗糙的;粗俗的

scarcely

[’skeəsli]

adv.几乎不;简直不;刚刚;决不

collateral

[kə’lætərəl]

adj.旁系的;并行的;附属的

descendant

[dɪ’sendənt]

n.后裔;子孙;后代

earlier

[’ɜːlɪə]

adj.早的;初期的

optic

[’ɒptɪk]

adj.视觉的;光学的

pigment

[’pɪɡmənt]

n. 色素; 颜料

crustacean

[krʌ’steɪʃn]

n.甲壳类动物

cornea

[’kɔːniə]

n.角膜

facet

[’fæsɪt]

n.小平面;方面;刻面

swelling

[’swelɪŋ]

n.肿胀物;膨胀,

transparent

[træns’pærənt]

adj.透明的;明显的;清晰的

cone

[kəʊn]

n.圆锥体;锥形物

lateral

[’lætərəl]

adj.侧面的;横向的;旁边的

convex

[’kɒn’veks]

adj.中凸的;凸圆的;凸面的

treatise

[’triːtɪs]

n.论文;论述;故事

eagle

[’iːɡl]

n.鹰

startlingly

[’stɑːtlɪŋli]

v.惊人地

continual

[kən’tɪnjuəl]

adj.不断的;频繁的;连续的

thickness

[’θɪknəs]

n.厚度;浓度;层

alteration

[ˌɔːltə’reɪʃn]

n.改变;变更

multiply

[’mʌltɪplaɪ]

vt.乘;增加

infinite

[’ɪnfɪnət]

adj.无穷的;无限的

pick

[pɪkt]

采摘，挑选；

canal

[kə’næl]

n.运河;沟渠

respire

[rɪ’spaɪə(r)]

v.〈正式或文〉(人)呼吸;(植物)呼吸;松口气

excrete

[ɪk’skriːt]

v.排泄;分泌

larva

[’lɑːvə]

n.幼虫;幼体

exterior

[ɪk’stɪəriə(r)]

n.外部;外表;外景

gill

[ɡɪl]

n.鳃;菌褶;及耳(液量单位)

duct

[dʌkt]

n.管道;导管

vascular

[’væskjələ(r)]

adj.血管的

partition

[pɑː’tɪʃn]

n.划分;隔离物

obliterate

[ə’blɪtəreɪt]

v.涂去;擦去;删除;盖销(邮票等)

respiration

[ˌrespə’reɪʃn]

n.呼吸;【生】一次呼吸，呼吸量;植物呼吸作用

accessory

[ək’sesəri]

n.附件;配件

complement

[’kɒmplɪment]

vt.相辅相成

physiologist

[ˌfɪzi’ɒlədʒɪst]

n.生理学家

homologous

[hə’mɒləɡəs]

adj.相应的;一致的;【生物】同源的

prototype

[’prəʊtətaɪp]

n.原型;范例;雏形

orifice

[’ɒrɪfɪs]

n.孔

slit

[slɪt]

n.裂缝;狭长的切口

artery

[’ɑːtəri]

n.动脉;干线

embryo

[’embriəʊ]

n.胚胎;萌芽

utterly

[’ʌtəli:]

adv.完全;全然;绝对

gradual

[’ɡrædʒuəl]

adj.逐渐的;逐步的;平缓的

entertain

[ˌentə’teɪn]

v.娱乐;使有兴趣;招待;考虑;抱有;容纳

naturalist

[’nætʃrəlɪst]

n.自然主义者;博物学者

probability

[ˌprɒbə’bɪləti]

n.可能性

sticky

[’stɪki]

adj.粘的;闷热的;困难的;令人不满意的

secretion

[sɪ’kriːʃn]

n.分泌;分泌物;藏匿

hatch

[hætʃ]

n.孵化;舱口，舱口盖

adhesive

[əd’hiːsɪv]

adj.有粘性的;胶粘的

undoubted

[ʌn’daʊtɪd]

adj.无疑的

fertile

[’fɜːtaɪl]

adj.肥沃的;富饶的;能繁殖的;多产的;(创造力)丰富的

ray

[reɪ]

n.光线;射线;辐射

affinity

[ə’fɪnəti]

n.姻亲;密切关系;吸引力

inheritance

[ɪn’herɪtəns]

n.遗传;遗产;继承;继承物

geology

[dʒi’ɒlədʒi]

n.地质学;(某地区的)地质情况;地质学的著作

luminous

[’luːmɪnəs]

adj.发光的;发亮的;清楚的;明白易懂的

parallel

[’pærəlel]

adj.平行的

independently

[ˌɪndɪ’pendəntli]

adv.独立地;自立地

invariably

[ɪn’veəriəbli]

adv.不变地;总是;一贯地

deviation

[ˌdiːvi’eɪʃn]

n.偏离;出轨;背弃

correlate

[’kɒrəleɪt]

vt.使相互关联

pasture

[’pɑːstʃə(r)]

n.牧场;草原

quadruped

[’kwɒdruped]

n.四足动物

incessant

[ɪn’sesnt]

adj.不断的;无尽的

harass

[’hærəs]

vt.使疲乏;骚扰

hare

[heə(r)]

n.野兔

reversion

[rɪ’vɜːʃn]

n.返回;逆转;恢复;反向

bamboo

[ˌbæm’buː]

n.竹子

climber

[’klaɪmə(r)]

n.爬山者;攀登者;攀援植物;野心家

wallow

[’wɒləʊ]

v.打滚;沉溺于;(船等)颠簸

suture

[’suːtʃə(r)]

n.缝合

unimportant

[ˌʌnɪm’pɔːtnt]

adj.不重要的

domesticate

[də’mestɪkeɪt]

vt.驯养;使专注于家务;教化

savage

[’sævɪdʒ]

a. 野蛮的，未开化的;

subsistence

[səb’sɪstəns]

n.生存;生计;存在

susceptibility

[səˌseptə’bɪləti]

n.敏感性;感受性;磁化率(复数)susceptibilities:感情.

poison

[’pɔɪzn]

n.毒药;毒害;败坏道德之事

ignorance

[’ɪɡnərəns]

n.无知;愚昧

adduce

[ə’djuːs]

v.引证;举出

reasoning

[’riːzənɪŋ]

n.推论;推理;论证

possessor

[pə’zesə(r)]

n.持有人;所有人

allowance

[ə’laʊəns]

n.津贴

fang

[fæŋ]

n.尖牙;毒牙

rattle

[’rætl]

vi. 发出格吱声；呱哒响;

curl

[kɜːl]

n.卷曲;卷发;年轮;漩涡;【足】曲线球

doom

[duːm]

n.毁灭;厄运;判决;死亡

advantageous

[ˌædvən’teɪdʒəs]

adj.有利的;有助的;有益的

lapse

[læps]

n.过失;流逝;间隔;堕落;失效

myriad

[’mɪriəd]

adj.无数的

endemic

[en’demɪk]

adj.风土的;地方的

Zealand

[ˈziːlənd]

n.西兰岛(丹麦最大的岛)

legion

[’liːdʒən]

n.军团;众多的人

contrivance

[kən’traɪvəns]

n.机械装置;发明的才能;想出的办法;人工痕迹

backward

[’bækwəd]

adj.向后的

viscus

[’vɪskəs]

n.内脏;腑脏

gall

[ɡɔːl]

v.擦伤;烦恼;激怒;羞辱

intensify

[ɪn’tensɪfaɪ]

vt.增强;强化;加剧

drone

[drəʊn]

n. 【U】嗡嗡声;

slaughter

[’slɔːtə(r)]

n.残杀;屠杀;大量杀戮

instinctive

[ɪn’stɪŋktɪv]

adj.本能的;天性的;直觉的

hatred

[’heɪtrɪd]

n.仇恨;憎恨;敌意;怨恨

maternal

[mə’tɜːnl]

adj.母亲的;母系的;母方的;母性的

fortunate

[’fɔːtʃənət]

adj.幸运的;侥幸的;带来幸运的

pollen

[’pɒlən]

n.花粉

granule

[’ɡrænjuːl]

n.小粒;微粒

waft

[wɒft]

v.飘浮;飘荡

ovule

[’ɒvjuːl]

n.胚珠;卵子

indefinite

[ɪn’defɪnət]

adj.模糊的;不确定的;无限期的

grind

[ɡraɪnd]

v.磨;压迫;碾碎;磨得吱吱响;逐渐停顿

impossibility

[ɪmˌpɒsə’bɪləti]

n.不可能之事;不可能

homology

[hɒ’mɒlədʒɪ]

n.同源;相同;同系;异性同体

excretion

[ɪk’skriːʃn]

n.排泄;分泌;排泄物

inorganic

[ˌɪnɔː’ɡænɪk]

adj.无机的;非自然生长的

illustrious

[ɪ’lʌstriəs]

adj.著名的;杰出的

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