 This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Today's reading by Daniel Harris. The Origin of Species by Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life. Sixth London Edition by Charles Darwin. Chapter number six. Part one. Difficulties of the Theory. Chapter contents include difficulties of the theory of descent with modification, 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, modes of transition, cases of difficulty, natural non-fesit seldom, 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. Long before the reader has arrived at this part of my work, a crowd of difficulties will have occurred to him. Some of them are so serious that to this day I can hardly reflect on them without being in some degree 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 the theory. These difficulties and objections may be classed under the following heads. First, why? If species have descended from other species by 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? 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 other animal with wildly different habits and structure? Can we believe that natural selection could produce, on the one hand, an organ of trifling importance, such as the tail of a giraffe, which serves as a fly flapper, and, on the other hand, an organ so wonderful as the eye? Thirdly, can instincts be acquired and modified to natural selection? What shall we say to the instinct, which leads the bee to make cells, and which has practically anticipated the discoveries of profound mathematicians? Fourthly, how can we account for species, when crossed, being sterile and producing sterile offspring, whereas, when varieties are crossed, their fertility is unimpaired? The first two heads will be here discussed. Some miscellaneous objections in the following chapter. Instinct and hybridism in the two succeeding chapters. 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 form, and other less favored forms with which it comes into competition. Thus, extinction and natural selection go hand in hand. Hence, if we look at each species as descended from some unknown form, both the parent and all the transitional varieties will generally have been exterminated by the very process of the formation and perfection of the new form. 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 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 crust of the earth is a vast museum, but the natural collections have been imperfectly made and only at long intervals of time. 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 our specimens taken from the metropolis inhabited by each. By my theory, these allied species are 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 form 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 the large part explained. 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 most continents have 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 the 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. 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 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 Alpha de Kendo has observed, a common alpine species disappears. The same fact has been noted by E. 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. 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 not for other competing species, that nearly all either prey on or service prey for others, in short, that each organic being is either directly or indirectly related in the most important manner to other organic beings, 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 lives, or by which it is destroyed, or with which it comes into competition. And as these species are already defined objects, 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 less than numbers, will, during fluctuations in the number of its enemies or of its prey, or in the nature of the seasons, be extremely liable to utter extermination, and thus its geographical range will come to be still more sharply defined. As allied or representative species, when inhabiting a continuous area, are generally distributed in such a manner that each has a wide range, with a comparatively narrow neutral territory between them, in which they become rather suddenly rarer and rarer, as varieties do not essentially differ from species, the same rule will probably apply to both. And if we take a varying species inhabiting 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 the 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. Aza Gray, and Mr. Woliston, 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 conclude that varieties linking two other varieties together generally have existed in lesser numbers than the forms which they connect, then we can understand why intermediate varieties should not endure for a very long periods. Why? As a general rule, they should be exterminated and disappear, sooner than the forms which they originally linked together. 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 it is a far more important consideration that during the process of further modification by which two varieties are supposed 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 have a better chance within any given period of presenting further favorable 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 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 the wide plains in 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 favor 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. 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 intermediate lengths. First, because new varieties are very slowly formed, per variation is a slow process and natural selection can do nothing until favorable individual differences or variations occur, and until a place in the natural polity of a country can be better fitted by some modification of someone 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 to see only a few species being slight modifications of structure in some degree permanent. In this, assuredly, we do see. Secondly, areas now continuous must often have existed within the recent period as isolated portions, in which many forms, more especially among the classes which unite for each birth and one or much, may have separately been rendered sufficiently distinct to rank as a representative species. In this case, intermediate varieties between the several representative species and their common parent have existed within each isolated portion of the land, but these links, during the process of natural selection, will have been supplanted and exterminated so that they will no longer be found in a living state. 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. Intermediate varieties will, from reasons already assigned, namely from what we know of the actual distribution of closely allied or representative species and likewise knowledge 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. These, from existing in greater numbers, will, in the aggregate, present more varieties and thus be further improved through natural selection and gain further advantages. Lastly, looking not to any one time, but at all time, if my theory be true, numberless intermediate varieties, linking closely together all the species of the same group, must assuredly have existed, but the very process of natural selection constantly tends, as has been so often remarked, to exterminate the parent forms in the intermediate links. Consequently, evidence of their former existence could be found only among fossil remains, which are preserved, as we shall attempt to show in a future chapter, in an extremely imperfect and intermittent record. On the origin and transition of organic beings with peculiar habits and structure, it has been asked by the opponents of such views as I hold, how, for instance, could a land carnivorous animal 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 there now exists a carnivorous animal presenting close intermediate grades from strictly terrestrial to aquatic habits, and, as each exists by struggle for life, it is clear that each must be well adapted to its place in nature. Look at the mastella vision 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 dies for and preys on fish, but during the long winter, it leaves the frozen waters and preys, like other pole cats, on mice and land animals. If a different case had been taken and it had been asked how an insectivorous quadruped could possibly have converted into a flying bat, the question would have been far more difficult to answer. Yet I think such difficulties have little weight. Here, as on other occasions, I lie under a heavy disadvantage, for out of the many striking cases which I have collected, I can only give one or two instances of transitional habits and structures in allied species, and of diversified habits, either consonant 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. Look at the family of squirrels. Here we have the finest gradation from animals with their tails only slightly thumbed, and from others, as Sir Richardson has remarked, with posterior parts 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, expansive 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 a reason to believe, to lessen 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 possible conditions. Let the climate and vegetation change. The other competing rodents are 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 the numbers or become exterminated, unless they also become 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. Now look at the galliopithecus or the so-called flying lemur which is formally ranked among bats but is now believed to belong to the insectivoria. An extremely wide flank membrane stretches from the corner of the jaw to the tail and includes the limbs with elongated fingers. This flank membrane is furnished with an extensor muscle although no graduated links of structure fitted for gliding through the air now collect the galliopithecus with other insectivoria yet there is no difficulty in supposing that such links formally existed that each was developed in the same manner as with the less perfectly gliding squirrels each grade of structure having been useful to its possessor nor can I see any insuperable difficulty in further believing it possible that the membrane connected fingers and forearm of the galliopithecus might have been greatly lengthened by natural selection and this as far as your organs of flight are concerned would have converted the animal into a bat. In certain bats in which the wing membrane extends from the top of the shoulder to the tail and includes the hind legs we perhaps see traces of an apparatus originally fitted for gliding through the air rather than for flight. If a voted dozen genera of birds were to become extinct who had a venture to surmise that birds might have existed which used their wings solely as flappers like the logger headed duck micropeturus of eitn as fins in the water and as front legs on the land like the penguin as sails like the ostrich and functionally for no purpose like the apterus 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 wing structure here alluded to which perhaps may all be the result of disuse indicate the steps by which birds actually acquire their perfect power of flight but they serve to show what diversified means of transition are at least possible seeing a few members of such water breeding classes as the crustacea and moluska are adapted to live on the land and seeing that we have flying birds and mammals flying insects of the most diversified types and formally have 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 affected who would have ever imagined that in an early transitional state they had been inhabitants of the open ocean and have user in sipping organs of flight exclusively so far as we know to escape being devoured by other fish when we see any structure highly perfected for any particular habit as the wings of a bird for flight we should bear in mind the animals displaying early transitional grades of the structure will seldom have survived to the present day for they will have been supplanted by their successors which were gradually rendered more perfect through natural selection furthermore we may conclude that transitional states between structures fitted for very different habits of life will rarely have been developed in early period and great numbers in under many subordinate forms thus to return to our imaginary illustration of the flying fish it does not seem probable that fish is 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 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 I will now give two or three instances both have diversified and have changed habits in the individuals of the same species in our case it would be easy for natural selection to adapt the structure of the animal to its changed habits or exclusively to one of its several habits it is however difficult to decide an immaterial for us whether habits generally changed first in structure afterwards or whether slight modifications of structure lead to changed habits both probably often occurring 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 Sarofagus sulphuratus in South America hovering over one spot and then proceeding to another like a kestrel in the other time standing stationary on the margin of water and then dashing into it like a kingfisher out of fish in our own country the larger titmouse, Paris major may be seen climbing branches almost like a creeper it's sometimes like a strike it's called small birds by blows on the head and I have many times seen and heard it hammering the seeds of the ewe on a branch and thus breaking them like a nut hatch in North America the black bear was seen by herds swimming for hours with wildly open mouth thus catching almost like a whale insects in the water as we sometimes see individuals following habits different from those proper to their species and to the other species of the same genus I might expect that such individuals would occasionally give rise to new species having anomalous habits and with their structure other slightly or considerably modified from that of their type and such instances occur in nature can a more striking instance of adaptation be given than that of a woodpecker for climbing trees and 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 on the plains of La Plata where hardly a tree grows there is a woodpecker which has two toes before and two behind a long pointed tongue pointed tail feathers sufficiently stiff to support the bird in vertical position on a post but not so stiff as in the typical woodpeckers and a straight strong beak the beak however is not so straight or so strong as in the typical woodpeckers but is strong enough to bore into wood hence this copatas in all the essential parts of its structure is a woodpecker even in such trifling characters as the coloring, the harsh tone of the voice and undulatory flight its close blood relationship to a common woodpecker is plainly declared yet as I can assert not only from my own observations but from those of the accurate Azara in certain large districts it does not climb trees and it makes its nest in holes and banks in certain other districts however this same woodpecker as Mr. Hudson states frequents trees and bores holes in the trunk for its nest I may mention as another illustration of the varied habits of this genus that a Mexican copatas has been described by Dessasur as boring holes into hard wood in order to lay up a store of acorns Petrels are the most aerial of oceanic birds but in the quiet sounds of Tierra del Fuego the Puffinaria, Berardi in its general habits in its astonishing power of diving in its manner of swimming and flying when made to take flight would be mistaken by anyone for an ock or a greb nevertheless it is essentially a petrol but with many parts of its organization profoundly modified in relation to its new habits of life whereas the woodpecker of La Plata has had its structure only slightly modified in the case of the water Ouzal the acutus observer by examining its dead body would never have suspected its subaquatic habits yet this bird, which is allied to the thrush family subsists by diving using its wings underwater grasping stones with its feet as of the great order of Hymenopoteris insects are terrestrial accepting the genus Proctotrups which Sir John Lubbock has discovered to be aquatic in its habits it often enters the water and dives about by the use not of its legs but of its wings and remains as long as four hours beneath the surface yet exhibits no modification in structure in accordance with its abnormal habits he who believes each being has been created and now see it must occasionally have felt surprised when he has met with an animal having habits in structure not in agreement what can be planer than that the webbed feet of ducks and geese are formed for swimming yet there are upland geese with webbed feet which rarely go near the water and no one except Audubon has seen the frigate bird which has all its four toes webbed a light on the surface of the ocean on the other hand they can be aquatic although their toes are only bordered by membrane what seems planer than that the long toes not furnished with membrane of the Grellators are formed for walking over swamps and floating plants the water hand and land rail are members of this order yet the first is nearly as aquatic as the coot and the second is nearly as terrestrial as the quail or partridge in such cases again habits have changed without a corresponding change of structure the webbed feet of the upland goose may be said to have become almost 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 he who believes in separate and innumerable acts of creation may say that in these cases it has pleased creator to cause a being of one type of one belonging to 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 its numbers and that if anyone being varies ever so little either in habits or structure and thus gains an advantage over some other inhabitant of the same country it will seize on the place of that inhabitant however different that may be from its own place hence it will cause them no surprise that there should be geese and frigate birds with webbed feet living on the dry land and rarely alighting on the water that there should be long toed corn crakes living in meadows instead of in swamps that there should be woodpeckers where hardly a tree grows that there should be diving thrushes and diving hymenopatera and petrels with the habits of ox organs of extreme perfection and complication to suppose that the eye with all its inimitable contrivances for adjusting to 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 degree when it was first said that the sun stood still and the world turned round the common sense of mankind declared the doctrine false but the old saying of Vox Populi Vox Dei as every philosopher knows cannot be trusted in science reason tells me that if numerous gradations from a simple and imperfect eye to one complex imperfect can be shown to exist each gray being useful to its possessor as is certainly the case if further the eye ever varies and the variations be inherited is likewise certainly the case and if such variations should be useful to any animal under changing conditions of life then the difficulty of believing that a perfect and complex eye could be formed by natural selection though unsuperable by our imagination should not be considered as subversive of the theory how a nerve comes to be sensitive to light hardly concerns us more than how life itself originated but I may remark that as some of the lowest organisms in which nerves cannot be detected are capable of perceiving light it does not seem impossible that certain sensitive elements in their sarcos should become aggregated and developed into nerves endowed with this special sensibility in searching for the gradations through which an organ in any species has been perfected we ought to look exclusively to its linear progenitors but this is scarcely ever possible and we are forced to look to other species in genera of the same group that is to the collateral descendants from the same parent form in order to see what gradations are possible and for the chance of some gradations having been transmitted in an unaltered or little altered condition but the state of the same organ in distinct classes may incidentally throw light on the steps by which it has been perfected the simplest organ which can be called an eye consists of an optic nerve surrounded by pigment cells and covered by translucent skin without any lens or any other refractive body we may however, according to Monsieur Jordan, descend even a step lower and find aggregates of pigment cells apparently serving his organs vision without any nerves and resting merely on sarcotic tissue either the above simple nature are not capable of distinct vision and serve only to distinguish light from darkness in certain starfishes small depressions in the layer of pigment which surrounds the nerve are filled as described by the author just quoted with transparent gelatinous matter projecting with a convex service like the cornea in the higher animals he suggests that this serves not to form an image but only to concentrate the luminous rays and render their perception more easy in this concentration of the rays we gain the first and by far the most important step towards the formation of a true picture forming eye we have only to place a naked extremity of an optic nerve which in some of the lower animals lies deeply buried in the body and in some near the surface at the right distance from the concentrating apparatus and an image will be formed on it in the great class of the articulata we may start from an optic nerve simply coated with pigment the latter sometimes forming a sort of pupil but destitute of lens or other optical contrivance with insects it is now known that the numerous facets of the cornea of their great compound eyes form true lenses and that the cones include curiously modified nervous filaments but these organs in the articulata are so much diversified that Muller formally made three main classes with seven subdivisions besides a fourth main class of aggregated simple eyes when we reflect on these facts here given much too briefly with respect to the wide diversified and graduated range of structure in the eyes of the lower animals and when we bear in mind how small the number of all living forms must be in comparison with those which have become extinct the difficulty ceases to be very great in believing that natural selection may have converted the simple apparatus of an optic nerve coated with pigment and invested by transparent membrane into an optical instrument as perfect as is possessed by any member of the articulata class he who will go thus far ought not to hesitate to go one step further if he finds on finishing this volume that large bodies effects otherwise inexplicable can be explained by the theory of modification through natural selection he ought to admit that a structure even as perfect as an ego's eye might thus be formed although in this case he does not know the transitional states it has been objected that in order to modify the eye and still preserve it as a perfect instrument many changes would have to be affected simultaneously which it is assumed could not be done through natural selection but as I have attempted to show my work on the variation of domestic animals it is not necessary to suppose that the modifications were all simultaneous if they were extremely slight and gradual different kinds of modification would also serve for the same general purpose as Mr Wallace has remarked if a lens has too short or too long of focus it may be amended either by alteration of curvature or an alteration of density if the curvature be irregular and the rays do not converge to a point then any increased regularity of curvature will be an improvement so the contraction of the iris and the muscular movements of the iron neither of them are essential to vision but only improvements which might have been added and perfected at any stage of the construction of the instrument within the highest division of the animal kingdom namely the vertebrata we can start from an eye so simple that it consists, as in the Lancelot of a little sack of transparent skin furnished with a nerve and lined with pigment but destitute of any other apparatus in fishes and reptiles as Owen has remarked the range of gradation from diopteric structures is very great it is a significant fact that even a man according to the high authority of Virchow the beautiful crystalline lens is formed in the embryo by an accumulation of epidermic cells lying in a sac-like fold of the skin and the vitreous body is formed from everyonic subcutaneous tissue to arrive however at a just conclusion regarding the formation of the eye with all its marvelous yet not absolutely perfect characters is indispensable that the reason should conquer the imagination but I have felt the difficulty far too keenly to be surprised at others hesitating to extend the principle of natural selection to so startling a length it is scarcely possible to avoid comparing the eye with 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 interference be presumptuous is there 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 an imagination to take a thick layer of transparent tissue with spaces filled with fluid and 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 thickness place 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 represented by natural selection or the survival of the fittest always intently watching each slight alteration in the transparent layers and carefully preserving each which under varied circumstances in any way or degree tends to produce a distincter image we must suppose each new state of the instrument to be multiplied by a million each to be preserved until a better is produced and then the old ones to be all destroyed in living bodies variation will cause the slight alteration generation will multiply them almost infinitely and natural selection will pick up with unerring skill each improvement let this process go on for millions of years during each year on millions of individuals of many kinds and may we not believe that this performing obstacle instrument might thus be formed as superior to one of glass as it works for the creator or to those of man modes of transition 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 I doubt many organs exist of which we do not know the transitional grades more especially if we look to much isolated species around which according to the theory there has been much extinction or again if we take an organ common to all the members of a class for in this latter case the organ must have been originally formed at a 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 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 among the lower animals of the same organ performing at the same time wholly distinct functions thus in the larva of the dragonfly and in the fish cobytes the elementary canal respires digests and excretes 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 specialize if any advantage were thus gained the whole or part of an organ which had previously performed two functions for one function alone and in sensible steps greatly change its nature many plants are known which regularly produce at the same time differently constructed flowers and as such plants were to produce one kind alone a great change would be affected with comparative suddenness in the character of the species it is however probable that the two sorts of flowers born by the same plant were originally differentiated by finally graduated steps which may still be followed in some few cases again two distinct organs or the same organ under two very different forms may simultaneously perform in the same individual the same function and this is an extremely important means of transition to give one instance there are fish with gills or brachini that breathe the air dissolved in the water at the same time that they breathe free air in their swim bladders this latter organ being divided by highly vascular partitions and having a ductus pneumaticus for the supply of air to give another instance from the vegetable kingdom plants climb by three distinct means by spirally twining by clasping a support with their sensitive tendrils and by the emission of aerial rootlets these three means are usually found in distinct groups but some few species exhibit two of the means or even all three in the same individual in all such cases one of the two organs might readily be modified and perfected so as to perform all the work being aided during the process of modification by the other organ then this other organ might be modified for some other and quite distinct purpose or be wholly obliterated the illustration of the swim bladder 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 widely different purpose namely respiration the swim bladder has also been worked in as an accessory to the auditory organs of certain fishes all physiologists admit that the swim bladder is homologous or ideally similar in position and structure with the lungs of the higher vertebrae animals hence there is no reason to doubt that the swim bladder has actually been converted into lungs or an organ used exclusively for respiration according to this view it may be inferred that all vertebrae animals with true lungs are descended by ordinary generation from an ancient and unknown prototype which was furnished with a floating apparatus or swim bladder 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 vertebrae the bronchiae have wholly disappeared but in the embryo the slits on the side of the neck and the loop-like course of the utteries still mark their former position but it is conceivable that the now utterly lost brachyne might have been gradually worked in by natural selection for some distinct purpose for instance, landois has shown that the wings of insects are developed from the trachea it is therefore highly probable that in this great class organs which once served for respiration have been actually converted into organs for flight in considering transitions of organs it is so important in mind the probability of conversion from one function to another that I will give another instance pedunculated chiropenes have two minute folds of skin called by me ovigorous frena which serve through a means of sticky secretion to retain the eggs until they are hatched within the sac these chiropetes have no brachyne the whole surface of the body and of the sac together with the small frena serving for respiration the balandi or cecily chiropetes on the other hand have no ovigorous frena the eggs lying loose at the bottom of the sac within the well enclosed shell but they have in the same relative position with the frena large much folded membranes which freely communicate with the circulatory lacunae of the sac and body in which have been considered by all naturalist as brachyne now I think no one will dispute that the ovigorous frena in the one family are strictly homologous with the other brachyne of the other family indeed they graduate into each other therefore it need not be doubted that the two little folds of skin which originally served as ovigorous frena which likewise very slightly aided in the act of respiration have been gradually converted by natural selection into brachyne simply through an increase in their size and the obliteration of their adhesive glands if all pedunculated chiropetes have become extinct and they have suffered far more extinction than have cecily chiropetes who could ever have imagined that the brachyne in this latter family had originally existed as organs for preventing the ova from being washed out of the sac there is another possible mode of transition namely through the acceleration of the period of reproduction this has lately been insisted on by Professor Cope and others in the United States it is now known that some animals are capable of reproduction at a very early age before they have acquired their perfect characters and if this power became thoroughly well developed to the species it seems probable that the adult stage of development would sooner or later be lost and in this case especially if the larva differed much from the mature form the character of the species would be greatly changed and degraded again, not a few animals after arriving at maturity go on changing in character during nearly their whole lives with mammals for instance the form of the skull is often much altered with age of which Dr. Murray has given some striking instance with seals all LibriVox recordings are in the public domain for more information or to volunteer please visit LibriVox.org today's reading by Daniel Harris the origin of species by means of natural selection or the preservation of favored races in the struggle for life sixth London edition by Charles Darwin chapter number six part two difficulties of the theory everyone knows how the horns of stags become more and more branched and the plumes of some birds become more finely developed as they grow older Professor Cope states that the teeth of certain lizards change much in shape with the advancing years with crustaceans not only many trivial but some important parts assume a new character as recorded by Fritz Müller after maturity in all such cases and many could be given if the age for reproduction were retarded the character of the species at least in its adult state would be modified nor is it improbable that the previous and earlier stages of development would in some cases be hurried through and finally lost whether species have often been modified through this comparatively sudden mode of transition I can form no opinion but if this has occurred it is probable that the differences between the young and the mature and between the mature and the old were primordially acquired by graduated steps special difficulties of the theory of natural selection although we must be extremely cautious in concluding that any organ could not have been produced by excessive small transitional gradations yet undoubtedly serious cases of difficulty occur one of the most serious is that of neuter insects which are often 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 for it is impossible to conceive by what steps these wondrous organs have been produced but this is not surprising for we do not even know of what use they are in the gymnatus and torpedo they no doubt serve as powerful means of defense and perhaps for securing prey yet in the ray as observed by metucci an analogous organ in the tail manifests but little electricity even when the animal is greatly irritated so that it can hardly be of any use for the above purposes moreover in the ray besides the organ just referred to there is as dr. r mcdonnell has shown another organ near the head not known to be electrical but which appears to be the real homolog of the electric battery in the torpedo it is generally admitted that there exists between these organs an ordinary muscle a close analogy and an intimate structure in the distribution of the nerves and in the matter in which they are acted on by various reagents it should also be especially observed that muscular contraction is accompanied by an electrical discharge and as dr. Radcliffe insists in the electrical apparatus of the torpedo during rest there would seem to be a charge in every respect like that which is met with in muscle and motor nerve during the rest and the discharge of the torpedo instead of being peculiar may be only another form of the discharge which tends upon the action of muscle and motor nerve beyond this we cannot at present go in the way of explanation but as we know so little about the uses of these organs and as we know nothing about the habits and structure of the progenitors of the existing electric fishes it would be extremely bold to maintain that no serviceable transitions are possible by which these organs might have been gradually developed these organs appear at first offer another and far more serious difficulty for they occur in about a dozen kinds of fish of which several are widely remote in their affinities when the same organ is found in several members of the same class especially if in members having very different habits of life we may generally attribute its presence to inheritance from a common ancestor and its absence in some of the members to loss through disuse or natural selection so that if the electric organs have been inherited from some one ancient progenitor we might have expected that all electric fishes would have been specially related to each other but this is far from the case nor does geology at all lead to the belief formally possessed electric organs which their modified descendants have now lost but when we look at the subject more closely we find in the several fishes provided with electric organs that they are situated in different parts of the body that they differ in construction as in the arrangement of plates and according to Piscini in the process or means by which the electricity is excited and lastly in being supplied with different nerves proceeding from different sources and this is perhaps the most important of all the differences hence in the several fishes furnished with electric organs these cannot be considered as homologous but only as analogous in function consequently there is no reason to suppose that they have been inherited from a common progenitor for had this been the case they would have closely resembled each other in sex thus the difficulty of an organ apparently the same arising in several remotely allied species disappears leaving only the lesser yet still great difficulty namely by which graduated steps these organs have been developed in each separate groups of fishes the luminous organs which occur in a few insects belonging to wildly different families in which are situated in different parts of the body offer under our present state of ignorance a difficulty almost exactly parallel with that of electric organs other similar cases could be given for instance in plants the very curious contrivance of a mass of pollen grains born on a footstock with an adhesive gland is apparently the same in orcas and aslepas genera almost as remote as is possible among flowering plants the parts are not homologous in all cases of beings far removed from each other in the scale of organization which are furnished with similar and peculiar organs it will be found that although the general appearance and function of the organs may be the same yet fundamental differences between them can always be detected for instance the eyes of selaffods or cuttlefish and of vertebrae animals appear wonderfully alike and in such wildly sundered groups no part of this resemblance can be due to inheritance from a common progenitor Mr. Mivart has advanced this case as one of special difficulty but I am unable to see the force of his argument an organ for vision must be formed transparent tissue and must include some sort of lens for throwing an image at the back of a darkened chamber beyond this superficial resemblance there is hardly any real similarity between the eyes of cuttlefish and vertebrates as may be seen by consulting Henson's admirable memoir on these organs in the selaffoda is impossible for me to enter here on details but I may specify a few of the points of difference the crystalline lens in the higher cuttlefish consists of two parts placed one behind the other like two lenses both having a very different structure and disposition to what occurs in the vertebrata the retina is wholly different with an actual inversion of the elemental parts with a large nervous ganglion included within the membranes of the eye the relations of the muscles are as different as it is possible to conceive and so on other points hence it is not a little difficult to decide how far even the same terms ought to be employed in describing the eyes of the selaffoda and the vertebrata it is, of course open to anyone to deny that the eye in either case could have been developed through the natural selection of successive slight variations but if this be admitted in the one case it is clearly possible in the other and fundamental differences of structure in the visual organs of two groups might have been anticipated in accordance with this view of their manner of formation as two men of sometimes independently hit on the same invention so in the several foregoing cases it appears that natural selection working for the good of each being and taking advantage of all favourable variations has produced similar organs as far as function is concerned and distinct organic beings which owe none of their structure in common to inheritance from a carbon progenitor Fritz Muller in order to test the conclusions derived at in this volume has followed out with much care a nearly similar line of argument several families of crustaceans include a few species possessing an air breathing apparatus and fitted to live out of the water and two of these families which are more especially examined by Muller which are nearly related to each other the species agree most closely in all important characters namely in their various organs circulating systems in the position of the tufts of hair within their complex stomachs and lastly in the whole structure of the water breathing Brachini even to the microscopic hooks by which they are cleansed hence it might have been expected that in the few species belonging to both families which live on the land the equally important air breathing apparatus would have been the same for why should this one apparatus for the same purpose have been made to differ while all the other important organs were closely similar or rather identical Fritz Muller argues that this close similarity in so many points of structure must in accordance with the views advanced by me be accounted for by inheritance from a common progenitor but as the vast majority of the species in the above two families as well as with most other crustaceans are aquatic in their habits it is improbable in the highest degree that their common progenitor should have been adapted for breathing air Muller has thus led carefully to examine the apparatus in the air breathing species and he found it to differ in several important points as in the position of the orifices in the manner in which they are open and close and in some accessory details now such differences are intelligible and might even have been expected on the supposition that species belonging to distinct families had slowly become adapted to live more and more out of water and to breathe the air for these species from belonging to distinct families would have differed to a certain extent and in accordance with the principle that the nature of each variation depends on two factors vis the nature of the organism and that of the surrounding conditions their variability assuredly would not have been exactly the same consequently natural selection would have had different materials or variations to work on in order to arrive at the same functional result and the structures thus acquired would almost necessarily have differed on the hypothesis of several acts of creation the whole case remains unintelligible this line of argument seems to have had great weight in leading for his Muller to accept the views maintained by me in this volume another distinguished zoologist the late Professor Klapalder has argued in the same manner and has arrived at the same result he shows that there are parasitic mites, a cardinai belonging to distinct sub-families and families which are furnished with hair claspers these organs must have been independently developed as they could not have been inherited from the same progenitor and in the several groups they are formed by the modification of the four legs of the hind legs of the maxili or lifts and of appendages on the underside of the hind part of the body in the foregoing cases we see the same end gained and the same function performed in beings not at all or only remotely allied by organs in appearance closely similar on the other hand it is a common rule throughout nature that the same end should be gained even sometimes in the case of closely related beings by the most diversified means how differently constructed is the feathered wing of a bird and the membrane covered wing of a bat and still more so the four wings of a butterfly the two wings of a fly and the two wings with the elitra of the beetle bival shells are made open and shut but on what a number of patterns is the hinge constructed from the long row of neatly interclocking teeth in a nuclear to the simple ligament of a muscle seeds are disseminated by their minuteness by their capsule being converted into a light balloon like envelope by being embedded in pulp or flesh formed by most diverse parts and rendered nutritious as well as conspicuously colored so as to attract and be devoured by birds by having hooks and grapples of many kinds and serrated ons so as to adhere to the fur of quadrupeds and by being furnished with wings and plumes as different in shape as they are elegant in structure so as to be wafted by every breeze I will give one other instance for this subject of the same end being gained by the most diversified means well deserves attention some authors maintain that organic beings have been formed in many ways for the sake of mere variety almost like toys in a shop but such a view of nature is incredible with plants having separated sexes and with those in which though hermaphrodites the pollen does not spontaneously fall on the stigma some aid is necessary for their fertilization with several kinds this is affected by the pollen grains which are light and incoherent being blown by the wind through mere chance onto the stigma and this is the simplest plan which can well be conceived and almost equally simple though a very different plan incurs in many plants in which a symmetrical flower secretes a few drops of nectar and is consequently visited by insects and these carry on the pollen from the anthers to the stigma from this simple stage we may pass through an inexhaustible number of contrivances all for the same purpose and affected in essentially the same manner but entailing changes in every part of the flower the nectar may be stored in variously shaped repticepticles with its stem and pestilis modified in many ways sometimes forming trap-like contrivances and sometimes capable of neatly adapted movements through irritability or elasticity from such structures we may advance till we come to such a case of extraordinary adaptation as that lately described by Dr. Kruger in the Choranthes this orchid has part of its labellum and or lower lip hollowed into a great bucket into which drops of almost pure water continually fall from two secreting horns and when the bucket is half full the water overflows by a spout on one side the basal part of the labellum stands over the bucket and is itself hollowed out into a sort of chamber with two lateral entrances within this chamber there are curious fleshy ridges the most ingenious man if he had not witnessed what takes place could never have imagined what purpose all these parts serve Dr. Kruger saw crowds of large humblebees visiting the gigantic flowers of this orchid not in order to suck nectar but can gnaw off the ridges within the chamber above the bucket in doing this they frequently pushed each other into the bucket and their wings being thus wetted they could not fly away but were compelled to crawl out through the passage formed Dr. Kruger thus saw a continual procession of bees crawling out of their involuntary bath the passage is narrow and is roofed over by the column so that a bee enforcing its way out first rubs its back against the viscid stigma and then against the viscid glance of the pollen masses the pollen masses are thus glued to the back of the bee and it begins to crawl out through the passage of a lately expanded flower and are thus carried away Dr. Kruger sent me a flower in spirits of wine with a bee which he had killed before it had quite crawled out with a pollen mass still faceted into its back when the bee thus provided flies to another flower or to the same flower a second time and is pushed by its comrades into the bucket and then crawls out by the passage the pollen mass necessarily comes first into contact with the viscid stigma and adheres to it and the flower is fertilized now at last we see the full use of every part of the flower of the water secreting horns of the bucket half full of water which prevents the bees from flying away and forces them to crawl out in an awkwardly placed viscid pollen masses and the viscid stigma the construction of the flower in another closely allied orchid namely the Catacium is widely different though serving the same end and is equally curious bees visit these flowers like those of the Corianthes in order to gnaw the Lebelum in doing this they inevitably touch a long tapering sensitive protection or as I have called it the antenna this antenna when touched transmits a sensation or vibration to a certain membrane which is instantly ruptured this sets free a spring by which the pollen mass is shot forth like an arrow in the right direction and adheres by its viscid extremity to the back of the bee the pollen mass of the male plant for the sexes are separate in this orchid is thus carried to the flower plant where it is brought into contact with the stigma which gives viscid enough to break certain elastic threads and retain the pollen thus affecting fertilization how it may be asked in the forgoing and innumerable other instances can we understand the graduated scale of complexity and the multifarious means for gaining the same end the answer no doubt is as already remarked that when two forms vary which already differ from each other in some slight degree the variability will not be of the same exact nature and consequently the results obtained through natural selection for the same general purpose will not be the same we should also bear in mind that every highly developed organism has passed through many changes and that each modified structure tends to be inherited so that each modification will not readily be quite lost but may be again and again further altered hence the structure of each part of each species for whatever purpose it may serve is the sum of many inherited changes through which the species has passed during successive adaptations to change habits and conditions of life finally then although in many cases it is most difficult even to conjecture by what transitions organs could have arrived at their present state yet considering how small the proportion of living known forms is to the extinct and unknown I have been astonished how rarely an organ can be named towards which no transitional grade is known to lead it is certainly true that new organs appearing as have created for some special purpose rarely or never appear in any being as indeed is shown by that old but someone exaggerated canon in natural history of natura non facete 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 niggered in innovation why on the theory of creation should there be so much variety and so little real novelty why should all the parts and organs of many independent beings each supposed to have been separately created for its own proper place in nature be so commonly linked together by graduated steps why should not nature take a sudden leap from structure to structure on the theory of natural selection we can clearly understand why she should not for natural selection acts only by taking advantage of slight successive variations she can never take a great and sudden leap but must advance by the short and sure through slow steps organs of little apparent importance as affected by natural selection as natural selection acts by life and death by the survival of the fittest and by the destruction of the less well fitted individuals I sometimes felt great difficulty in understanding the origin or formation of parts of little importance almost as great though of a very different kind as in the case of the most perfect and complex organs 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've given instances of very trifling characters such as the down on fruit and the color of its flesh the color of the skin and hair of quadrupeds which from being correlated with constitutional differences or from determining the attacks of insects 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 this could have been adapted for its present purpose by successive slight modifications each better and better fitted for so trifling an object as the drive-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 depend 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 with great advantage it is not that the larger quadrupeds are actually destroyed except in some rare cases by 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 organs now of trifling importance have probably in some cases been of high importance to an early later and after having been slowly perfected at a former period have been transmitted to existing species in nearly the same state although now a very slight use but any actually injurious deviations in their structure would of course 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 and so many land animals which in their lungs are modified swim bladders betray their aquatic origin may perhaps be thus accounted for a well-developed tail having been formed in an aquatic animal 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 in the case of the dog the aid in this latter respect or the any tail can double still more quickly in the second place we may easily err in attributing importance to characters and in believing that they have been developed through natural selection we must by no means overlook the effects of the definite action of changed conditions of life of so-called spontaneous variations which seem to depend in a quite subordinate degree on the nature of the conditions of the tendency to reversion of the wrong-laws characters of the complex laws of growth such as correlation, comprehension of the pressure of one part on another etc. and finally of sexual selection by which characters of use to one sex are often gained and then transmitted more or less perfectly to the other sex though of no use to the sex but structures thus indirectly gained although at first no advantage to a species may subsequently have been taken advantage of by its modified descendants under new conditions of life and newly acquired habits if green woodpeckers alone had existed and we did not know that there were many black and pied kind I dare say that we should have thought that the green color was a beautiful adaptation to conceal this tree-frequenting bird from its enemies and consequently that it was a character of importance that had been inquired through natural selection as it is the color is probably in chief part due to sexual selection a trailing paw in the Malay Arpeggio climbs a loftiest trees by it 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 as there is reason to believe from the distribution of the thorn-bearing species in Africa and South America serve as a defense against browsing quadrupeds so the spikes on the paw may at first have been developed for this object and subsequently have been improved and taken advantage of by the plant as it underwent further modification and became a climber the naked skin on the head of a vulture is generally considered as a direct adaptation for wallowing imputrity and so it may be or 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 and the skulls of 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 we are profoundly ignorant of the cause of each slight variation or individual difference and we are immediately made conscious of this by reflecting on the differences between the breeds of our domesticated animals in different countries more especially in the less civilized countries where there has been but little methodical selection. Animals kept by savages in different countries often have to struggle for their own subsidence and are exposed to a certain extent to natural selection and individuals with slightly different constitutions would succeed best under different climates with cattle susceptibility to the attacks of flies is correlated with color as is the liability to be poisoned by certain plants so that even color would thus be subjected to the action of natural selection. Some observers are convinced that a damp climate affects the growth of the hare and that with the hare the horns are correlated. Mountain breeds always differ from lowland breeds and a mountainous country would probably affect the high limbs from exercising them more and possibly even the forearm of the pelvis and then by the law of homologous variation the front limbs and the head would probably be affected. The shape also of the pelvis might affect the by pressure the shape of certain parts of the young in the womb. The laborious breathing necessary in high regions tends as we have good reason to believe to increase the size of the chest and again correlation would come into play. The effects of lessened exercise together with abundant food on the whole organization is probably still more important and this as H. von Nathousis has lately shown in his excellent treatise is apparently one chief cause of the great modification which the breeds of swine have undergone. But we are far too ignorant to speculate on the relative importance of the several known and unknown causes of variation and I have made the remarks only to show that if we are unable to account for the characteristic differences of our several domestic breeds which nevertheless are generally admitted to have arisen through ordinary generation from one or a few parent stocks we ought not to lay too much stress on our ignorance of the precise cause of the slight analogous differences between true species. Utilitarian doctrine how far true beauty how acquired The foregoing remarks lead me to say a few words on the protests lately made by some naturalists against a new utilitarian doctrine that every detailed structure has been produced for the good of its possessor. They believe that many structures have been created for the sake of beauty to delight man or the creator but this latter point is beyond the scope of scientific discussion or for the sake of mere variety a few already discussed. Such doctrines if true would be absolutely fatal to my theory. I fully admit that many structures are now of no direct use to their possessors and may never have been of any use to their progenitors but this does not prove that they were formed solely for beauty or variety. No doubt the definite action of change conditions and the various causes of modifications lately specified have all produced an effect probably a great effect independently of any advantage thus gained. But a still more important consideration is that the chief part of the organization of every living creature is due to inheritance and consequently, though each being assuredly is well fitted for its place in nature many structures have now no very close and direct relation to present habits of life. 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 similar 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 webbed feet, no doubt were as useful to the progenitor of the upland goose and of the frigate bird as they now are the most aquatic of living birds. So we may believe that the progenitor of the seal did not possess a flipper but a foot with five toes fitted for walking or gasping and we may further venture to believe that the several bones in the limbs of the monkey horse and bat were originally developed on the principle of utility probably through the reduction of more numerous bones in the fin of some ancient fish-like progenitor of the whole class. It is scarcely possible to decide how much allowance ought to be made for such causes of change as the definite action of external conditions so-called spontaneous variations and the complex laws of growth. But with these important exceptions we may conclude that the structure of every living creature either now is or was formerly of some direct or indirect use to its possessor. With respect to the belief that organic beings have been created beautiful for the delight of man, a belief which it has been pronounced is subversive of my whole theory, I must first remark that the sense of beauty obviously depends on the nature of the mind, irrespective of any real quality in the admired object and that the idea of what is beautiful is not innate or unalterable. We see this, for an instance, of men of different races admiring an entirely different standard of beauty in their women. If beautiful objects have been created solely for man's gratification it ought to be shown that before man appeared there was less beauty on the face of the earth than since he came on the stage. Were the beautiful voluot and cone shells of the Epulene epoch and the gracefully sculptured animites of the secondary period created that man by ages afterward admire them in his cabinet? Few objects are more beautiful than the minute salacious cases of Diomatikai were these created that they might be examined and admired under the higher powers of the microscope? The beauty in this latter case and in many others is apparently wholly due to the symmetry of growth. Flowers rank among the most beautiful productions of nature, but they have been rendered conspicuous in contrast with the green leaves, and in consequence of the same time beautiful so that they may be easily observed by insects. I have come to this conclusion from finding an invariable rule that when a flower is fertilized by the wind it never has a gaily colored corolla. Several plants habitually produce two kinds of flowers, one kind open and colored so as to attract insects, the other closed not colored, destitute of nectar and never visited by insects. Hence we may conclude that if insects had not been developed on the face of the earth our plants would not have been decked with beautiful flowers but it would have been produced with only with such poor flowers as we see on our fir, oak, nut, and ash trees on grasses, spinach, docks, and nettles which are all fertilized through the agency of wind. A similar line of argument holds good with fruits that a ripe strawberry or cherry is as pleasing to the eyes to the palate that the gaily colored fruit of the spindle wood-tree and the scarlet berries of the holly are beautiful objects will be emitted by everyone. But this beauty serves merely as a guide to birds and beasts in order that the fruit may be devoured and the matured seeds disseminated. I infer that this is the case from having as yet found no exception to the rule that seeds are always disseminated when embedded within a fruit of any kind, that is within a fleshy or pulpy envelope, if it is to be colored of any brilliant tint or rendered conspicuous by being white or black. On the other hand, I willingly admit that a great number of male animals, as are most gorgeous birds, some fishes, reptiles, and mammals and a host of magnificently colored butterflies have been rendered beautiful for beauty's sake. But this has been affected through sexual selection, that is, by the more beautiful males having been continually preferred by the females and not for the delight of man. So it is with the music of birds. We may infer from all this that a nearly similar taste for beautiful colors and for musical sounds runs through a large part of the animal kingdom. When the female is as beautifully colored as the male, which is not rarely the case with birds and butterflies, the cause apparently lies in the colors acquired through sexual selection having been transmitted to both sexes instead of to the males alone. How the sense of beauty in its simplest form, that is the reception of a peculiar kind of pleasure from certain colors, forms and sounds, was first developed in the mind of man, and of the lower animals, is a very obscure subject. The same sort of difficulty is presented if we can inquire how it is that certain flavors and odors give pleasure and others displeasure. Habit in all these cases appears to have come to a certain extent into play, but there must be some fundamental cause in the constitution of the nervous system in each species. Natural selection cannot possibly produce any modification in the species exclusively for the good of another species, though throughout nature one species incessantly takes advantage of, and profits by, the structures of others. But natural selection can and does often produce structures for the direct injury of other animals, as we see in the fang of the adder, and in the avipositor of the itchnumon 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 have 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 defense and for the destruction of its prey, but some authors suppose that at the same time it is furnished with a rattle for its own injury, namely to warn its prey. 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. It is a much more probable view that the rattlesnake uses its rattle, the cobra expands its frill, and the puff adder swells while hissing so loudly and harshly in order to alarm the many birds and beasts which are known to attack even the most venomous species. Snakes act on the same principle which makes the hen ruffle her feathers and expand her wings when a dog approaches her chickens. But I have not space here to enlarge on the many ways by which animals endeavour to frighten away their enemy. Natural selection will never produce in a being any structure more injurious than beneficial to that being, but 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, being will become extinct as myriads have become extinct. 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 comes into competition. We see that this is the standard 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 by Muller not to be perfect even in the most perfect organ, the human eye. Hemmholtz whose judgment no one will dispute after describing the strongest terms the wonderful powers of the human eye as these remarkable words. That which we have discovered in the way of inexactness and imperfection in the optical machine and in the image on the retina is as nothing in comparison with the incongruities which we have just come to cross in the domain of the sensations. One might say that nature has taken delight in accumulating contradictions in order to remove all foundation from the theory of a pre-existing harmony between the external and internal worlds. If our reason leads us to admire with enthusiasm a multitude of inimitable contrivances in nature, this same reason tells us that we may easily err on both sides, that some other contrivances are less perfect. Can we consider the sting of the B as perfect which when used against many kinds of enemies cannot be withdrawn owing to the backward serratures and thus invariably causes the death of the insect by tearing out its viscera? If we look at the sting of the B as having existed in a remote progenitor as a boring and serrated instrument like that in so many members of the same great order and that it has since been modified but not perfected for its present purpose with the position originally adapted for some other object such as produced gulls since 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 social community it will fulfill all the requirements of natural selection though 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, we can admire the production for the single purpose of thousands of drones which are utterly useless to the community for any other purpose 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 B which urges her to destroy the young queens, her daughters as soon as they are 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 principles of natural selection. If we admire the several ingenious contrivances by which orchids and many other plants are fertilized through insect agency can we consider as equally perfect the elaboration of dense clouds of pollen by our fir trees so that a few granules may be wafted by chance on to the ovules? Summary the law of unity of type and of the conditions of existence embraced by the theory of natural selection we have in this chapter discussed some of the difficulties and objections which may be urged against the theory many of them are serious but I think that in the discussion light has been thrown on several facts which on the belief 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 is always very slow and that any one time acts only on a few forms and partly because the very process of natural selection implies the continual simplanting distinction of proceeding 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 era an intermediate variety will often be formed fitted for an intermediate zone but for 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 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 only glided through air we have seen that a species under new conditions of life may change its habits or it may have diversified habits with some very unlike those of its nearest congeners hence we can understand bearing in mind that each organic wherever it can live how it has arisen that there are upland geese with webbed feet ground woodpeckers diving threshes and petrels with the habits of ox although the belief that an organ so perfect as the eye could have been formed by natural selection is enough to stagger anyone yet in the case of any organ if we know of a long series of gradations and complexity each good for its possessor then under changing conditions of life there is no logical impossibility in the requirement 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 extremely cautious in concluding that none can have existed for the metamorphosis of many organs show what wonderful changes 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 in part or in whole specialized for one function and two 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 transition we have seen that in two beings widely remote from each other in the natural scale organs serving for the same purpose and in external appearance closely similar may have been separately and independently form but when such organs are closely examined essential differences in their structure can almost always be detected and this naturally follows from the principle of natural selection on the other hand the common rule throughout nature is infinite diversity of structure for gaining the same end and this again naturally follows from the same principle in many cases we are far too ignorant to be enabled to assert that a part or organ is so unimportant for the welfare of a species that modifications in the structure cannot have been slowly accumulated by means of natural selection in many other cases modifications are probably the direct result of the laws of variation or of growth independently of any good having been thus gained but even such structures have often as we may feel assured been subsequently taken advantage of and still further modified for the good of species under new conditions of life we may also believe that a part formally of high importance has frequently been retained as the tale 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 means of natural selection natural selection can 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 possessor in each well stocked country natural selection acts through the competition of the inhabitants and consequently leads to success in the battle for life only in accordance with the standard of that particular country hence the inhabitants of one country generally the smaller one often yield to the inhabitants of another and generally larger country for in the larger country that will have existed more individuals and more diversified forms and the competition will have been severe and thus the standard selection will have been rendered higher natural selection will not necessarily lead to absolute perfection nor as far as we can judge by our limited faculties can absolute perfection be everywhere predicated on the theory of natural selection we can clearly understand the full meaning of that old canon in natural history natural non facet sultum this canon if we look to the present inhabitants alone of the world is not strictly correct but if we include all of those of past times whether known or unknown it must on this theory be strictly true 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 the 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 quiver is fully embraced by the principle of natural selection for natural selection acts by either now adapting the varying parts of each being to his organic and inorganic conditions of life or by having adapted them during past periods of time the adaptions being aided in many cases by the increased use or disuse of parts being affected by the direct action of external conditions of life and subjected in all cases to the several laws of growth and variation hence in fact the law of the conditions of existence is the higher law as it includes through the inheritance of former variations and adaptations that the unity of type end of chapter 6 part 2