 This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. 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 Four Natural Selection or the Survival of the Fittest Section Three of Three The probable effects of the action of natural selection through divergence of character and extinction on the descendants of a common ancestor. After the foregoing discussion, which has been much compressed, we may assume that the modified descendants of any one species will succeed so much the better as they become more diversified in structure and are thus enabled to encroach on places occupied by other beings. Now let us see how this principle of benefit being derived from divergence of character combined with the principles of natural selection and of extinction tends to act. The accompanying diagram will aid us in understanding this rather perplexing subject. Let A to L represent the species of a genus large in its own country. These species are supposed to resemble each other in unequal degrees as is so generally the case in nature and is represented in the diagram by the letters standing at unequal distances. I have said a large genus because as we saw in the second chapter on an average more species vary in large genera than in small genera and so the varying species of the large genera present a greater number of varieties. We have also seen that the species which are the commonest and most widely diffused vary more than do the rare and restricted species. Let A be a common widely diffused and varying species belonging to a genus large in its own country. The branching and diverging dotted lines of unequal lengths proceeding from A may represent its varying offspring. The variations are supposed to be extremely slight but of the most diversified nature. They are not supposed all to appear simultaneously but often after long intervals of time nor are they all supposed to endure for equal periods. Only those variations which are in some way profitable will be preserved or naturally selected and here the importance of the principle of benefit derived from divergence of character comes in. For this will generally lead to the most different or divergent variations represented by the outer dotted lines being preserved and accumulated by natural selection. When a dotted line reaches one of the horizontal lines and is there marked by a small numbered letter a sufficient amount of variation is supposed to have been accumulated to form it into a fairly well marked variety such as would be thought worthy of record in a systematic work. The intervals between the horizontal lines in the diagram may represent each a thousand or more generations. After a thousand generations species A is supposed to have produced two fairly well marked varieties namely A1 and M1. These two varieties will generally still be exposed to the same conditions which made their parents variable and the tendency to variability is in itself hereditary. Consequently they will likewise tend to vary and commonly in nearly the same manner as did their parents. Moreover these two varieties being only slightly modified forms will tend to inherit those advantages which made their parent A more numerous than most of the other inhabitants of the same country. They will also partake of those more general advantages which made the genus to which the parent species belonged a large genus in its own country and all these circumstances are favourable to the production of new varieties. If then these two varieties be variable the most divergent of their variations will generally be preserved during the next thousand generations. And after this interval variety A1 is supposed in the diagram to have produced variety A2 which will owing to the principle of divergence differ more from A than did variety A1. Variety M1 is supposed to have produced two varieties namely M2 and S2 differing from each other and more considerably from their common parent A. We may continue the process by similar steps for any length of time. Some of the varieties after each thousand generations producing only a single variety but in a more and more modified condition some producing two or three varieties and some failing to produce any. Thus the varieties or modified descendants of the common parent A will generally go on increasing in number and diverging in character. In the diagram the process is represented up to the ten thousandth generation and under a condensed and simplified form up to the fourteen thousandth generation. But I must here remark that I do not suppose that the process ever goes on so regularly as is represented in the diagram though in itself made somewhat irregular nor that it goes on continuously. It is far more probable that each form remains for long periods unaltered and then again undergoes modification nor do I suppose that the most divergent varieties are invariably preserved. A medium form may often long endure and may or may not produce more than one modified descendant for natural selection will always act according to the nature of the places which are either unoccupied or not perfectly occupied by other beings and this will depend on infinitely complex relations. But as a general rule the more diversified in structure the descendants from any one species can be rendered the more places they will be enabled to seize on and the more their modified progeny will increase. In our diagram the line of succession is broken at regular intervals by small numbered letters marking the successive forms which have become sufficiently distinct to be recorded as varieties but these breaks are imaginary and might have been inserted anywhere after intervals long enough to allow the accumulation of a considerable amount of divergent variation. As all the modified descendants from a common and widely diffused species belonging to a large genus will tend to partake of the same advantages which made their parent successful in life they will generally go on multiplying in number by diverging in character. This is represented in the diagram by the several divergent branches proceeding from A. The modified offspring from the later and more highly improved branches in the lines of descent will, it is probable, often take the place of and so destroy the earlier and less improved branches. This is represented in the diagram by some of the lower branches not reaching to the upper horizontal lines. In some cases no doubt the process of modification will be confined to a single line of descent and the number of modified descendants will not be increased although the amount of divergent modification may have been augmented. This case would be represented in the diagram if all the lines proceeding from A were removed accepting that from A1 to A10. In the same way the English racehorse and English pointer have apparently both gone on slowly diverging in character from their original stocks without either having given off any fresh branches or races. After 10,000 generations species A is supposed to have produced three forms A10, F10 and M10 which from having diverged in character during the successive generations will have come to differ largely but perhaps unequally from each other and from their common parent. If we suppose the amount of change between each horizontal line in our diagram to be excessively small these three forms may still be only well marked varieties but we have only to suppose the steps in the process of modification to be more numerous or greater in amount to convert these three forms into doubtful or at least into well defined species. Thus the diagram illustrates the steps in which the small differences distinguishing varieties are increased into the larger differences distinguishing species. By continuing the same process for a greater number of generations as shown in the diagram in a condensed and simplified manner we get eight species marked by the letters between A14 and M14 all descended from A. Thus as I believe species are multiplied and genera are formed. In a large genus it is probable that more than one species will vary. In the diagram I have assumed that a second species I has produced by analogous steps after 10,000 generations either two well marked varieties W10 and Z10 or two species according to the amount of change supposed to be represented between the horizontal lines. After 14,000 generations six new species marked by the letters N14 to Z14 are supposed to have been produced. In any genus the species which are already very different in character from each other will generally tend to produce the greatest number of modified descendants. For these will have the best chance of seizing on new and widely different places in the polity of nature. Hence in the diagram I have chosen the extreme species A and the nearly extreme species I as those which have largely varied and have given rise to new varieties and species. The other nine species marked by capital letters of our original genus may for long but unequal periods continue to transmit unaltered descendants and this is shown in the diagram by the dotted lines unequally prolonged upwards. But during the process of modification represented in the diagram another of our principles namely that of extinction will have played an important part. As in each fully stocked country natural selection necessarily acts by the selected form having some advantage in the struggle for life over other forms there will be a constant tendency for improved descendants of any one species to supplant and exterminate in each stage of descent their predecessors and their original progenitor for it should be remembered that the competition will generally be most severe between those forms which are most nearly related to each other in habits, constitution and structure. Hence all the intermediate forms between the earlier and later states that is between the less and more improved states of the same species as well as the original parent species itself will generally tend to become extinct so it probably will be with many whole collateral lines of descent which will be conquered by later and improved lines if however the modified offspring of a species get into some distinct country or become quickly adapted to some quite new station in which offspring and progenitor do not come into competition both may continue to exist if then our diagram be assumed to represent a considerable amount of modification species A and all the earlier varieties will have become extinct being replaced by eight new species A14 to M14 and species I will be replaced by six N14 to Z14 new species but we may go further than this the original species of our genus were supposed to resemble each other in unequal degrees this is so generally the case in nature species A being more nearly related to B, C and D than to the other species and species I more to G, H, K and L than to the others these two species A and I were also supposed to be very common and widely diffused species so that they must originally have had some advantage over most of the other species of the genus their modified descendants 14 in number at the 14,000th generation will probably have inherited some of the same advantages they have also been modified and improved in a diversified manner at each stage of descent so as to have become adapted to many related places in the natural economy of their country it seems therefore extremely probable that they will have taken the places of and thus exterminated not only their parents A and I but likewise some of the original species which were most nearly related to their parents hence very few of the original species will have transmitted offspring to the 14,000th generation we may suppose that only one F of the two species E and F which were least closely related to the other nine original species has transmitted descendants to this late stage of descent the new species in our diagram represented from the original 11 species will now be 15 in number owing to the divergent tendency of natural selection the extreme amount of difference in character between species A14 and Z14 will be much greater than that between the most distinct of the original 11 species the new species moreover will be allied to each other in a widely different manner of the eight descendants from A the three marked A14, Q14 and P14 will be nearly related having recently branched off from A10 B14 and F14 from having diverged at an earlier period from A5 will be in some degree distinct from the three first named species and lastly O14, E14 and M14 will be nearly related one to the other but from having diverged at the first commencement of the process of modification will be widely different from the other five species and may constitute a sub-genus or a distinct genus the six descendants from I will form two sub-genera or genera but as the original species I differed largely from A standing nearly at the extreme end of the original genus the six descendants from I will owing to inheritance alone differ considerably from the eight descendants from A the two groups moreover are supposed to have gone on diverging in different directions the intermediate species also and this is a very important consideration which connected the original species A and I have all become except F extinct and have left no descendants hence the six new species descended from I and the eight descendants from A will have to be ranked as very distinct genera or even as distinct sub-families thus it is as I believe that two or more genera are produced by descent with modification from two or more species of the same genus and the two or more parent species are supposed to be descended from some one species of an earlier genus in our diagram this is indicated by the broken lines beneath the capital letters converging in sub-branches downwards towards a single point this point represents a species the supposed progenitor of our several new sub-genera and genera it is worthwhile to reflect for a moment on the character of the new species F-14 which is supposed not to have diverged much in character but to have retained the form of F either unaltered or altered only in a slight degree in this case its affinities to the other 14 new species will be of a curious and circuitous nature being descended from a form that stood between the parent species A and I now supposed to be extinct and unknown it will be in some degree intermediate in character between the two groups descended from these two species but as these two groups have gone on diverging in character from the type of their parents the new species F-14 will not be directly intermediate between them but rather between types of the two groups and every naturalist will be able to call such cases before his mind in the diagram each horizontal line has hitherto been supposed to represent a thousand generations but each may represent a million or more generations it may also represent a section of the successive strata of the earth's crust including extinct remains we shall when we come to our chapter on geology have to refer again to this subject and I think we shall then see that the diagram relates on the affinities of extinct beings which though generally belonging to the same orders families or genera with those now living yet are often in some degree intermediate in character between existing groups and we can understand this fact for the extinct species lived at various remote epochs when the branching lines of descent had diverged less I see no reason to limit the process of modification as now explained to the formation of genera alone if in the diagram we suppose the amount of change represented by each successive group of diverging dotted lines to be great the forms marked A-14 to P-14 those marked B-14 and F-14 and those marked O-14 to M-14 will form three very distinct genera we shall also have two very distinct genera descended from I differing widely from the descendants of A these two groups of genera will thus form two distinct families or orders according to the amount of divergent modification supposed to be represented in the diagram and the two new families or orders are descended from two species of the original genus and these are supposed to be descended from some still more ancient and unknown form we have seen that in each country it is the species belonging to the larger genera which oftenest present varieties or incipient species this indeed might have been expected for as natural selection acts through one form having some advantage over other forms in the struggle for existence it will chiefly act on those which already have some advantage and the largeness of any group shows that its species have inherited from a common ancestor some advantage in common hence the struggle for the production of new and modified descendants will mainly lie between the larger groups which are all trying to increase in number one large group will slowly conquer another large group reduce its number and thus lessen its chance of further variation and improvement within the same large group the later and more highly perfected subgroups from branching out and seizing on many new places in the polity of nature will constantly tend to supplant and destroy the earlier and less improved subforms small and broken groups and subgroups will finally disappear looking to the future we can predict that the groups of organic beings which are now large and triumphant and which are least broken up that is which have as yet suffered least extinction will for a long period continue to increase but which groups will ultimately prevail no man can predict for we know that many groups formerly most extensively developed have now become extinct looking still more remotely to the future we may predict that owing to the continued and steady increase of the larger groups a multitude of smaller groups will become utterly extinct and leave no modified descendants and consequently that of the species living at any one period extremely few will transmit descendants to a remote futurity I shall have to return to this subject in the chapter on classification but I may add that as according to this view extremely few of the more ancient species have transmitted descendants to the present day and as all the descendants of the same species form a class we can understand how it is that there exist so few classes in each main division of the animal and vegetable kingdoms although few of the most ancient species have left modified descendants yet at remote geological periods the earth may have been almost as well peopled with species of many genera families, orders and classes as at the present day on the degree to which organization tends to advance natural selection acts exclusively by the preservation and accumulation of variations which are beneficial under the organic and inorganic conditions to which each creature is exposed at all periods of life the ultimate result is that each creature tends to become more and more improved in relation to its conditions this improvement invariably leads to the gradual advancement of the organization of the greater number of living beings throughout the world but here we enter on a very intricate subject for naturalists have not defined to each other's satisfaction what is meant by an advance in organization among the vertebra the degree of intellect and an approach in structure to man clearly come into play it might be thought that the amount of change which the various parts and organs pass through in their development from embryo to maturity would suffice as a standard of comparison but there are cases as with certain parasitic crustaceans in which several parts of the structure become less perfect so that the mature animal cannot be called higher than its larva von Baer's standard seems the most widely applicable and the best namely the amount of differentiation of the parts of the same organic being in the adult state as I should be inclined to add and their specialization for different functions or as Milne Edwards would express it the completeness of the division of physiological labor but we shall see how obscure this subject is if we look for instance to fishes among which some naturalists rank those as highest which, like the sharks, approach nearest to amphibians while other naturalists rank the common bony or teleostean fishes as the highest in as much as they are most strictly fish-like and differ most from the other vertebrate classes we see still more plainly the obscurity of the subject by turning to plants among which the standard of intellect is of course quite excluded and here some botanists rank those plants as highest which have every organ as sepals, petals, stamens and pistils fully developed in each flower whereas other botanists, probably with more truth look at the plants which have their several organs much modified and reduced in number as the highest if we take as the standard of high organization the amount of differentiation and specialization of the several organs in each being when adult and this will include the advancement of the brain for intellectual purposes natural selection clearly leads towards this standard for all physiologists admit that the specialization of organs in as much as in this state they perform their functions better is an advantage to each being and hence the accumulation of variations tending towards specialization is within the scope of natural selection on the other hand we can see bearing in mind that all organic beings are striving to increase at a high ratio and to seize on every unoccupied or less well occupied space in the economy of nature that it is quite possible for natural selection gradually to fit a being to a situation in which several organs would be superfluous or useless in such cases there would be retrogression in the scale of organization whether organization on the whole has actually advanced from the remotest geological periods to the present day will be more conveniently discussed in our chapter on geological succession but it may be objected that if all organic beings thus tend to rise in the scale how is it that throughout the world a multitude of the lowest forms still exist and how is it that in each great class some forms are far more highly developed than others why have not the more highly developed forms everywhere supplanted and exterminated the lower Lamarck who believed in an innate and inevitable tendency towards perfection in all organic beings seems to have felt this difficulty so strongly that he was led to suppose that new and simple forms are continually being produced by spontaneous generation science has not as yet proved the truth of this belief whatever the future may reveal on our theory the continued existence of lowly organisms offers no difficulty for natural selection or the survival of the fittest does not necessarily include progressive development it only takes advantage of such variations as arise and are beneficial to each creature under its complex relations of life and it may be asked what advantage as far as we can see would it be to an infusorian animal cure to an intestinal worm or even to an earthworm to be highly organized if it were no advantage these forms would be left by natural selection unimproved or but little improved and might remain for indefinite ages in their present lowly condition and geology tells us that some of the lowest forms as the infusoria and rhizopods have remained for an enormous period in nearly their present state but to suppose that most of the many now existing low forms have not in the least advanced since the first dawn of life would be extremely rash for every naturalist who has dissected some of the beings now ranked as very low in the scale must have been struck with their really wondrous and beautiful organization nearly the same remarks are applicable if we look to the different grades of organization within the same great group for instance in the vertebrata to the coexistence of mammals and fish among mammalia to the coexistence of man and the ornithorhynchus among fishes to the coexistence of the shark and the Lancelot and theoxus which latter fish in the extreme simplicity of its structure approaches the invertebrate classes but mammals and fish hardly come into competition with each other the advancement of the whole class of mammals or of certain members of this class to the highest grade would not lead to their taking the place of fishes physiologists believe that the brain must be bathed by warm blood to be highly active and this requires aerial respiration so that warm-blooded animals when inhabiting the water lie under a disadvantage in having to come continually to the surface to breathe with fishes members of the shark family would not tend to supplant the Lancelot for the Lancelot as I hear from Fritz Muller has as sole companion and competitor on the barren sandy shore of South Brazil an anomalous analyte the three lowest orders of mammals namely marsupials, edentata and rodents coexist in South America in the same region with numerous monkeys and probably interfere little with each other although organization on the whole may have advanced and be still advancing throughout the world yet the scale will always represent many degrees of perfection for the high advancement of certain whole classes or of certain members of each class does not at all necessarily lead to the extinction of those groups with which they do not enter into close competition in some cases as we shall hear after see lowly organized forms appear to have been preserved to the present day from inhabiting confined or peculiar stations where they have been subjected to less severe competition and where their scanty numbers have retarded the chance of favorable variations arising finally I believe that many lowly organized forms now exist throughout the world from various causes in some cases variations or individual differences of a favorable nature may never have arisen for natural selection to act on and accumulate in no case probably has time sufficed for the utmost possible amount of development in some few cases there has been what we must call retrogression of organization but the main cause lies in the fact that under very simple conditions of life a high organization would be of no service possibly would be of actual disservice as being of a more delicate nature and more liable to be put out of order and injured looking to the first dawn of life when all organic beings as we may believe presented the simplest structure how it has been asked could the first step in the advancement or differentiation of parts have arisen Mr. Herbert Spencer would probably answer that as soon as simple unicellular organisms came by growth or division to be compounded of several cells or became attached to any supporting surface his law that homologous units of any order become differentiated in proportion as their relations to incident forces become different would come into action but as we have no facts to guide us speculation on the subject is almost useless it is however an error to suppose that there would be no struggle for existence and consequently no natural selection until many forms had been produced variations in a single species inhabiting an isolated station might be beneficial and thus the whole mass of individuals might be modified or two distinct forms might arise but as I remarked towards the close of the introduction no one ought to feel surprise at much remaining as yet unexplained on the origin of species if we make due allowance for our profound ignorance on the mutual relations of the inhabitants of the world at the present time and still more so during past ages convergence of character Mr. H. C. Watson thinks that I have overrated the importance of divergence of character in which however he apparently believes and that convergence as it may be called has likewise played a part if two species belonging to two distinct though allied genera had both produced a large number of new and divergent forms it is conceivable that these might approach each other so closely that they would have all to be classed under the same genus and thus the descendants of two distinct genera would converge into one but it would in most cases be extremely rash to attribute to convergence a close and general similarity of structure in the modified descendants of widely distinct forms the shape of a crystal is determined solely by the molecular forces and it is not surprising that dissimilar substances should sometimes assume the same form but with organic beings we should bear in mind that the form of each depends on an infinitude of complex relations namely on the variations which have arisen these being due to causes far too intricate to be followed out on the nature of the variations which have been preserved or selected and this depends on the surrounding physical conditions and in a still higher degree on the surrounding organisms with which each being has come into competition and lastly on inheritance in itself a fluctuating element from innumerable progenitors all of which have had their forms determined through equally complex relations it is incredible that the descendants of two organisms which had originally differed in a marked manner should ever afterwards converge so closely as to lead to a near approach to identity throughout their whole organization if this had occurred we should meet with the same form independently of genetic connection recurring in widely separated geological formations and the balance of evidence is opposed to any such admission Mr Watson has also objected that the continued action of natural selection together with divergence of character would tend to make an indefinite number of specific forms as far as mere inorganic conditions are concerned it seems probable that a sufficient number of species would soon become adapted to all considerable diversities of heat, moisture etc but I fully admit that the mutual relations of organic beings are more important and as the number of species in any country goes on increasing the organic conditions of life must become more and more complex consequently there seems at first no limit to the amount of profitable diversification of structure and therefore no limit to the number of species which might be produced we do not know that even the most prolific area is fully stocked with specific forms at the Cape of Good Hope and in Australia which supports such an astonishing number of species many European plants have become naturalized but geology shows us that from an early part of the tertiary period the number of species of shells and that from the middle part of this same period the number of mammals has not greatly or at all increased what then checks an indefinite increase in the number of species the amount of life and I do not mean the number of specific forms supported on an area must have a limit depending so largely as it does on physical conditions therefore if an area be inhabited by very many species each or nearly each species will be represented by few individuals and such species will be liable to extermination from accidental fluctuations in the nature of the seasons or in the number of their enemies the process of extermination in such cases would be rapid whereas the production of new species must always be slow imagine the extreme case of as many species as individuals in England and the first severe winter or very dry summer would exterminate thousands on thousands of species rare species and each species will become rare if the number of species in any country becomes indefinitely increased will, on the principle often explained present within a given period few favourable variations consequently the process of giving birth to new specific forms would thus be retarded when any species becomes very rare close interbreeding will help to exterminate it authors have thought that this comes into play in accounting for the deterioration of the aurochs in Lithuania of red deer in Scotland and of bears in Norway, etc lastly, and this I am inclined to think is the most important element a dominant species which has already beaten many competitors in its own home will tend to spread and supplant many others Alfons de Candol has shown that those species which spread widely tend generally to spread very widely consequently they will tend to supplant and exterminate several species in several areas and thus check the inordinate increase of specific forms throughout the world Dr Hooker has recently shown that in the southeast corner of Australia where apparently there are many invaders from different quarters of the globe the endemic Australian species have been greatly reduced in number how much weight to attribute to the several considerations I will not pretend to say but conjointly they must limit in each country the tendency to an indefinite augmentation of specific forms summary of chapter if under changing conditions of life organic beings present individual differences in almost every part of their structure and this cannot be disputed if there be owing to their geometrical rate of increase a severe struggle for life at some age, season or year and this certainly cannot be disputed then considering the infinite complexity of the relations of all organic beings to each other and to their conditions of life causing an infinite diversity in structure, constitution and habits to be advantageous to them it would be a most extraordinary fact if no variations had ever occurred useful to each being's own welfare in the same manner as so many variations have occurred useful to man but if variations useful to any organic being ever do occur assuredly individuals thus characterized will have the best chance of being preserved in the struggle for life and from the strong principle of inheritance these will tend to produce offspring similarly characterized this principle of preservation or the survival of the fittest I have called natural selection it leads to the improvement of each creature in relation to its organic and inorganic conditions of life and consequently in most cases to what must be regarded as an advance in organization nevertheless low and simple forms will long endure if well fitted for their simple conditions of life natural selection on the principle of qualities being inherited at corresponding ages can modify the egg, seed or young as easily as the adult among many animals sexual selection will have given its aid to ordinary selection by assuring to the most vigorous and best adapted males the greatest number of offspring sexual selection will also give characters useful to the males alone in their struggles or rivalry with other males and these characteristics will be transmitted to one sex or to both sexes according to the form of inheritance which prevails whether natural selection has really thus acted in adapting the various forms of life to their several conditions and stations must be judged by the general tenor and balance of evidence given in the following chapters but we have already seen how it entails extinction and how largely extinction has acted in the world's history geology plainly declares natural selection also leads to divergence of character for the more organic beings diverge in structure habits and constitution by so much the more can a large number be supported on the area of which we see proof by looking to the inhabitants of any small spot and to the productions naturalized in foreign lands therefore during the modification of the descendants of any one species and during the incessant struggle of all species to increase in numbers the more diversified the descendants become the better will be their chance of success in the battle for life thus the small differences distinguishing varieties of the same species steadily tend to increase till they equal the greater differences between species of the same genus or even of distinct genera we have seen that it is the common the widely diffused and widely ranging species belonging to the larger genera within each class which vary most and these tend to transmit to their modified offspring that superiority which now makes them dominant in their own countries natural selection as has just been remarked leads to divergence of character and to much extinction of the less improved and intermediate forms of life on these principles the nature of the affinities and the generally well defined distinctions between the innumerable organic beings in each class throughout the world may be explained it is a truly wonderful fact the wonder of which we are apt to overlook from familiarity that all animals and plants throughout all time and space should be related to each other in groups subordinate to groups in the manner which we everywhere behold namely varieties of the same species most closely related species of the same genus less closely and unequally related forming sections and subgenera species of distinct genera much less closely related and genera related in different degrees forming subfamilies, families, orders, subclasses and classes the several subordinate groups in any class cannot be ranked in a single file but seem clustered around points and these round other points and so on in almost endless cycles if species had been independently created no explanation would have been possible of this kind of classification but it is explained through inheritance and the complex action of natural selection entailing extinction and divergence of character as we have seen illustrated in the diagram the affinities of all the beings of the same class have sometimes been represented by a great tree I believe this similarly largely speaks the truth the green and budding twigs may represent existing species and these produced during former years may represent the long succession of extinct species at each period of growth all the growing twigs have tried to branch out on all sides and to overtop and kill the surrounding twigs and branches in the same manner as species and groups of species have at all times over mastered other species in the great battle for life the limbs divided into great branches and these into lesser and lesser branches were themselves once when the tree was young budding twigs and this connection of the former and present buds by ramifying branches may well represent the classification of all extinct and living species in groups subordinate to groups of the many twigs which flourished when the tree was a mere bush only two or three now grown into great branches yet survive and bear the other branches so with the species which lived during long past geological periods very few have left living and modified descendants from the first growth of the tree many a limb and branch has decayed and dropped off and these fallen branches of various sizes may represent those whole orders families and genera which have now no living representatives and which are known to us only in a fossil state as we here and there see a thin, straggling branch springing from a fork low down in a tree and which by some chance has been favoured and is still alive on its summit so we occasionally see an animal like the ornithorincus or lepidocyrin which in some small degree connects by its affinities two large branches of life and which has apparently been saved from fatal competition by having inhabited a protected station as buds give rise by growth to fresh buds and these if vigorous branch out and over top on all sides many a feebler branch so by generation I believe it has been with the great tree of life which fills with its dead and broken branches the crust of the earth and covers the surface with its ever branching and beautiful ramifications