 This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, visit LibriVox.org. The Origin of the Species by Natural Selection. Or The Preservation of Favored Races in the Struggle for Life. Sixth London Edition by Charles Darwin. Chapter 11. On the Geological Succession of Organic Beans. Part 2. On the Affinities of Extinct Species to Each Other and to Living Forms. Let us now look to the Mutual Affinities of Extinct and Living Species. All fall into a few grand classes. And this fact is at once explained on the principle of dissent. The more ancient any form is, the more, as a general rule, it differs from living forms. But as Buckland long ago remarked, Extinct Species can be classed either in still existing groups or between them. That the extinct forms of life help to fill up the intervals between existing genera, families, and orders is certainly true. But as this statement has often been ignored or even denied, it may be well to make some remarks on this subject and to give some instances. If we can find our attention either to the living or to the extinct species of the same class, the series is far less perfect than if we combine both into one general system. In the writings of Professor Owen, we continually meet with the expression of generalized forms as applied to extinct animals. And in the writings of Agassiz, of prophetic or synthetic types, and these terms imply that such forms are in fact intermediate or connecting links. Another distinguished paleontologist, Monsieur Gaudry, has shown in the most striking manner that many of the fossil animals discovered by him in Attica serve to break down the intervals between existing genera. Cuvier ranked the ruminants and pachyderms as two of the most distinct orders of mammals. But so many fossil links have been disintuned that Owen has had to alter the whole classification and has placed certain pachyderms in the same suborder with ruminants. For example, he dissolves by gradations the apparently wide interval between the pig and the camel. The ungolada of hoofed quadrupeds are now divided into the even-toed or odd-toed divisions. But the macruchania of South America connects to a certain extent these two grand divisions. No one will deny that the hyparion is intermediate between the existing horse and certain other ungulate forms. What a wonderful connecting link in the chain of mammals is the typotherium from South America, as the name given to it by Professor Gervais expresses, and which cannot be placed in any existing order. The sirenia form, a very distinct group of the mammals, and one of the most remarkable peculiarities in existing dugong and lemington, is the entire absence of hind limbs, without even a rudiment being left. But the extinct halotharium had, according to Professor Flower, an ossified thigh bone quote, articulated to a well-defined acetabulum in the pelvis, close quote. And it thus makes some approach to ordinary hoofed quadrupeds, to which the sirenia are in other respects allied. The cetaceans or whales are widely different from all other mammals, but the tertiary swigladon and squalidon, which have been placed by some naturalists in an order by themselves, are considered by Professor Huxley to be undoubtedly cetaceans, and quote, to constitute connecting links with the aquatic carnivora, close quote. Even the wide interval between birds and reptiles has been shown by the naturalist, just quoted, to be partially bridged over in the most unexpected manner, on the one hand, by the ostrich and the extinct archioterics, and on the other hand, by the chomsognathus, one of the denosarians, that group which includes the most gigantic of all terrestrial reptiles. Turning to the invertebrata, baron deserts, a higher authority could not be named, that he is every day taught that although paleozoic animals can certainly be classed under existing groups, yet that at this ancient period the groups were not so distinctly separated from each other as they now are. Some riders have objected to any extinct species or group of species being considered as intermediate between any two living species, or groups of species. If by this term it is meant that an extinct form is directly intermediate in all its characters between the two living forms or groups, the objection is probably valid. But in a natural classification, many fossil species certainly stand between living species and some extinct genera between living genera, even between genera belonging to distinct families. The most common case, especially with respect to very distinct groups such as fish and reptiles, seems to be that supposing them to be distinguished at the present day by a score of characters, the ancient members are separated by a somewhat lesser number of characters, so that the two groups formally made a somewhat nearer approach to each other than they now do. It is a common belief that the more ancient a form is, by so much the more it tends to connect by some of its characters, groups now widely separated from each other. This remark, no doubt, must be restricted to those groups which have undergone much change in the course of geological ages, and it would be difficult to prove the truth of the proposition. For every now and then, even a living animal, as the Lepidocirin, is discovered having affinities directed towards very distinct groups. Yet if we compare the older reptiles and bell-traitians, the older fish, the older cephalopods, and the eocene mammals with the recent members of the same classes, we must admit that there is truth in the remark. Let us see how far these facts and several inferences accord with the theory of descent with modification. As the subject is somewhat complex, I must request the reader to turn to the diagram in the fourth chapter. We may suppose that the numbered letters and italics represent genera, and the dotted lines diverging from them the species in each genus. The diagram is much too simple, too few genera and too few species being given, but this is unimportant for us. The horizontal lines may represent successive geological formations, and all the forms beneath the uppermost line may be considered as extinct. The three existing genera, A14, Q14, P14, will form a small family, B14 and F14, a closely allied family, or subfamily, and O14, I14, M14, a third family. These three families, together with the many extinct genera on the several lines of descent diverging from the parent form, A, will form an order, for all will have inherited something in common from their ancient progenitor. On the principle of the continued tendency to divergence of character, which was formally illustrated by this diagram, the more recent any form is, the more it will generally differ from its ancient progenitor. Hence, we can understand the rule that the most ancient fossils differ most from existing forms. We must not, however, assume that divergence of character is a necessary contingency. It depends solely on the descendants from a species being thus enabled to seize on many and different places in the economy of nature. Therefore, it is quite possible, as we have seen in the case of some Silurian forms, that a species might go on being slightly modified in relation to its slightly altered conditions of life, and yet retain throughout a vast period the same general characteristics. This is represented in the diagram by the letter capital F14. All the many forms, extinct and recent, descended from A, make, as before remarked, one order, and this order, from the continued effects of extinction and divergence of character, has become divided into several sub-families and families, some of which are supposed to have perished at different periods, and some to have endured to the present day. By looking at the diagram, we can see that if many of the extinct forms supposed to be embedded in these successive formations were discovered at several points low down in the series, the three existing families on the uppermost line would be rendered less distinct from each other. If, for instance, the genera A1, A5, A10, F8, M3, M6, M9 were disinterred, these three families would be so closely linked together that they probably would have to be united into one great family in nearly the same manner as has occurred with ruminants and certain pachyderms. Yet he who objected to consider as intermediate the extinct genera, which thus linked together the living genera of three families, would be partly justified, for they are intermediate, not directly, but only by a long and circuitous course through many widely different forms. If many extinct forms were to be discovered above one of the middle horizontal lines, or geological formations, for instance, above number seven, but none from beneath this line, then only two of the families, those on the left hand A14, etc., and B14, etc., would have to be united into one, and there would remain two families which would be less distinct from each other than they were before the discovery of the fossils. So, again, if the three families formed of a genera A14 to M14 on the uppermost line, be supposed to differ from each other by half a dozen important characters, then the families which existed at the period marked seven would certainly have differed from each other by a less number of characters, for they would, at this early stage of descent, have diverged in a less degree from their common progenitor. Thus it becomes that ancient and extinct genera are often in a greater or less degree intermediate in character between their modified descendants or between their collateral relations. Under nature, the process will be far more complicated than is represented in the diagram, for the groups will have been more numerous, they will have endured for extremely unequal lengths of time, and will have been modified in various degrees. As we possess only the last volume of the geological record, and that in a very broken condition, we have no right to expect, except in rare cases, to fill up the wide intervals in the natural system and thus to unite distinct families or orders. All that we have a right to expect is that those groups which have, within known geological periods, undergone much modification, should in the older formations make some slight approach to each other, so that the older members should differ less from each other in some of their characters than do the existing members of the same groups, and this by the concurrent evidence of our best paleontologists is frequently the case. Thus on the theory of descent with modification, the main facts with respect to the mutual affinities of the extinct forms of life to each other and to living forms are explained in a satisfactory manner, and they are wholly inexplicable on any other view. On this same theory, it is evident that the fauna during any one great period into the Earth's history will be intermediate and general character between that which preceded and that which succeeded it. Thus the species which lived at the sixth great stage of descent in the diagram are the modified offspring of those which lived at the fifth stage and are the parents of those which became still more modified at the seventh stage. Hence they could hardly fail to be nearly intermediate in character between the forms of life above and below. We must however allow for the entire extinction of some preceding forms and in any one region for the immigration of new forms from other regions and for a large amount of modification during the long and blank intervals between the successive formations. Subject to these allowances, the fauna of each geological period undoubtedly is intermediate in character between the preceding and succeeding faunas. I need give only one instance, namely the manner in which the fossils of the Devonian system when this system was first discovered were at once recognized by paleontologists as intermediate in character between those of the overlying Carboniferous and underlying Silurian systems. But each fauna is not necessarily intermediate as unequal intervals of time have elapsed between consecutive formations. It is no real objection to the truth of the statement that the fauna of each period as a whole is nearly intermediate in character between the preceding and succeeding faunas that certain genera offer exceptions to the rule. For instance, the species of mastodons and elephants when arranged by Dr. Falkner in two series in the first place according to their mutual affinities and in the second place according to their periods of existence do not accord an arrangement. The species extreme in character are not the oldest or the most recent nor are those which are intermediate in character, intermediate in age. But supposing for an instant in this and other such cases that the record of the first appearance and disappearance of the species was complete which is far from the case we have no reason to believe that forms successively produced necessarily endure for corresponding lengths of time. A very ancient form may occasionally have lasted much longer than a form elsewhere subsequently produced especially in the case of terrestrial productions inhabiting separated districts. To compare small things with great if the principal living and extinct races of the domestic pigeon were arranged in serial affinity this arrangement would not closely accord with the order and time of their production and even less with the order of their disappearance for the parent rock pigeon still lives and many varieties between the rock pigeon and the carrier have become extinct and carriers which are extreme and the important character of length of beak originated earlier than short-beaked tumblers which are at the opposite end of the series in this respect. Closely connected with the statement that the organic remains from an intermediate formation are in some degree intermediate in character is the fact insisted on by all paleontologists that fossils from two consecutive formations are far more closely related to each other than are the fossils from two remote formations. Pictit gives as a well-known instance the general resemblance of the organic remains from the several stages of the chalk formation though the species are distinct in each stage. This fact alone from its generality seems to have shaken professor Pictit in his belief in the immutability of species. He who is acquainted with the distribution of existing species over the globe will not attempt to account for the close resemblance of distinct species in closely consecutive formations by the physical conditions of the ancient areas having remained nearly the same. Let it be remembered that the forms of life at least those inhabiting the sea have changed almost simultaneously throughout the world and therefore under the most different climates and conditions consider the prodigious vicissitudes of climate during the Pleistocene period which includes the whole glacial epic and note how little the specific forms of the inhabitants of the sea have been affected. On the theory of descent the full meaning of the fossil remains from closely consecutive formations being closely related though ranked as distinct species is obvious. As the accumulation of each formation has often been interrupted and as long blank intervals have intervened between successive formations we ought not to expect to find as I attempted to show in the last chapter in any one or in any two formations all the intermediate varieties between the species which appeared at the commencement and close of these periods but we ought to find after intervals very long as measured by years but only moderately long as measured geologically closely allied forms or as they have been called by some authors representative species and these assuredly we do find. We find in short such evidence of the slow and scarcely sensible mutations of specific forms as we have the right to expect. On the state of development of ancient compared with living forms we have seen in the fourth chapter that the degree of differentiation and specialization of the parts in organic beings when arrived at maturity is the best standard as yet suggested of their degree of perfection or highness. We have also seen that as the specialization of parts is an advantage to each being so natural selection will tend to render the organization of each being more specialized and perfect and in this sense higher. Not but that it may leave many creatures with simple and unimproved structures fitted for simple conditions of life and in some cases will even degrade or simplify the organization yet leaving such degraded beings better fitted for their new walks of life. In another and more general manner new species become superior to their predecessors for they have to beat in the struggle of life all the older forms with which they come into close competition. We may therefore conclude that if under a nearly similar climate the eocene inhabitants of the world could be put into competition with the existing inhabitants the former would be beaten and exterminated by the latter as with the secondary by the eocene and the paleozoic by the secondary forms so that by this fundamental test of victory in the battle for life as well as by the standard of the specialization of organs modern forms ought on the theory of natural selection to stand higher than ancient forms. Is this the case? A large majority of paleontologists would answer in the affirmative and it seems that this answer must be admitted as true though difficult of proof. It is no valid objection to this conclusion that certain brachiopods have been but slightly modified from an extremely remote geological epic and that certain land and fresh water shells have remained nearly the same from the time when, as far as is known they first appeared. It is not an insuperable difficulty that Foramenophera have not as insisted on by Dr. Carpenter progressed in organization since even the Laurentian epic. For some organisms would have to remain fitted for simple conditions of life and what could be better fitted for this end than these lowly organized protozoa. Such objections as the above would be fatal to my view if it included advance in organization as a necessary contingent. They would likewise be fatal if the above Foramenophera, for instance, could be proved to have first come into existence during the Laurentian epic or the above brachiopods during the Cambrian formation. For in this case there would not have been time sufficient for the development of these organisms up to the standard which they had then reached. When advanced up to any given point there is no necessity on the theory of natural selection for their further continued process. Though they will during each successive age have to be slightly modified so as to hold their places in relation to slight changes in their conditions. The foregoing objections hinge on the question whether we really know how old the world is and at what period the various forms of life first appeared and this may be well disputed. The problem whether organization on the whole has advanced is in many ways excessively intricate. The geological record at all times imperfect does not extend far back enough to show with unmistakable clearness that within the known history of the world organization has largely advanced. Even at the present day looking to members of the same class naturalists are not unanimous which forms ought to be ranked as highest. Thus some look at the salaceans or sharks from their approach in some important points of structure to reptiles as the highest fish. Others look at the teleistians as the highest. The ganoids stand intermediate between the salaceans and the teleistians. The latter at the present day are largely preponderant in number but formerly salaceans and ganoids alone existed and in this case according to the standard of highness chosen so will it be said that fishes have advanced or retrograded in organization. To attempt to compare members of distinct types in the scale of highness seems hopeless. Who will decide whether a cuttlefish be higher than a bee? That insect which the great Bonbeer believed to be quote in fact more highly organized than a fish although upon another type. Close quote. In the complex struggle for life it is quite credible that Christosians not very high in their own class might beat cephalopods the highest mollusks and such Christosians though not highly developed would stand very high in the scale of invertebrate animals if judged by the most decisive of all trials the law of battle. Beside these inherent difficulties and deciding which forms are the most advanced in organization we ought not solely to compare the highest members of a class at any two periods though undoubtedly this is one and perhaps the most important element in striking a balance but we ought to compare all the members high and low at two periods. At an ancient epic the highest and lowest molluscoidal animals namely cephalopods and brachyopods swarmed in numbers and at the present time both groups are heavily reduced while others intermediate in organization have largely increased. Consequently some naturalists maintain that mollusks were formerly more highly developed than at present but a stronger case can be made out on the opposite side by considering the vast reduction of brachyopods and the fact that our existing cephalopods though few in number are more highly organized than their ancient representatives. We ought also to compare the relative proportional numbers at any two periods of the high and low classes throughout the world if for instance at the present day 50,000 kinds of vertebrate animals exist and if we knew that at some former time only 10,000 kinds existed we ought to look at this increase in number in the highest class which implies a great displacement of lower forms as a decided advance in the organization of the world. We thus see how hopelessly difficult it is to compare with perfect fairness under such extreme complex relations the standard of organization of the imperfectly known faunas of successive periods. We shall appreciate this difficulty more clearly by looking to certain existing faunas and flora from the extraordinary manner in which European productions have recently spread over New Zealand and have seized on places which must have been previously occupied by the indigenes we must believe that if all the animals and plants of Great Britain were set free in New Zealand a multitude of British forms would in the course of time become thoroughly naturalized there and would exterminate many of the natives. On the other hand from the fact that hardly a single inhabitant of the southern hemisphere has become wild in any part of Europe we may well doubt whether if all the productions of New Zealand were set free in Great Britain any considerable number would be enabled to seize on places now occupied by our native plants and animals. Under this point of view the productions of Great Britain stand much higher in the scale than those of New Zealand yet the most skillful naturalist from an examination of the species of the two countries could not have foreseen this result. Agassiz and several other highly competent judges insist that ancient animals resemble to a certain extent the embryos of recent animals belonging to the same classes and that the geological succession of extinct forms is nearly parallel with the embryological development of existing forms. This view accords well with our theory. In a future chapter we will attempt to show that the adult differs from its embryo owing to variations having supervened at a not early age and having been inherited at a corresponding age. This process whilst it leaves the embryo almost unaltered continually adds in the course of successive generations more and more difference to the adult. Thus the embryo acts as a sort of picture preserved by nature of the former and less modified condition of the species. This view may be true and yet may never be capable of proof. Seeing for instance that the oldest known mammals, reptiles and fishes strictly belong to their proper classes though some of these old forms are in a slight degree less distinct from each other but some of them are identical members of the same groups at the present day it would be vain to look for animals having the common embryological character of the vertebrata until beds rich in fossils are discovered far beneath the lowest Cambrian strata a discovery of which the chance is small. On to succession of the same types within the same areas periods. Mr. Cliff many years ago showed that the fossil mammals from the Australian caves were closely allied to the living marsupials of that continent. In South America a similar relationship is manifest even to an uneducated eye in the gigantic pieces of armor like those of the armadillo found in several parts of La Plata Professor Owen has shown in the most striking manner that most of the fossil mammals buried there in such numbers are related to South American types. This relationship is even more clearly seen in the wonderful collection of fossil bones made by Mature's Lund and Clausen in the caves of Brazil. I was so much impressed with these facts that in 1839 and 1845 I strongly insisted on this quote law of the succession of types on this wonderful relationship in the same continent between the dead and the living close quote. Professor Owen has subsequently extended the same generalization to the mammals of the old world we see the same law in this author's restorations of the extinct and gigantic birds of New Zealand we see it also in the birds of the caves of Brazil Mr. Woodward has shown that the same law holds good with seashells but from the wide distribution of most mollusks it is not well displayed by them. Other cases could be added as the relation between the extinct and living sand shells of Madera and between the extinct and living brackish water shells of the Oralo Caspian Sea. Now, what does this remarkable law of succession of the same types within the same areas mean? He would be a bold man who, after comparing the present climate of Australia and parts of South America and under the same latitude would attempt to account through dissimilar physical conditions for the dissimilarity of the inhabitants of these two continents and, on the other hand, through similarity of conditions for the uniformity of the same types in each continent during the latter tertiary periods. Nor can it be pretended that it is an immutable law that marsupials should have been chiefly or solely produced in Australia or that Edentata and other American types should have been solely produced in South America. For we know that Europe in ancient times was peopled by numerous marsupials and I have shown in the publications above alluded to that in America the law of distribution of terrestrial mammals was formally different from what it now is. North America formally partook strongly of the present character of the southern half of the continent and the southern half was formally more closely allied than it is at present to the northern half. In a similar manner we know from Falconer and Kotli's discoveries that northern India was more formally closely related in its mammals to Africa than it is at present time. Analogous facts could be given in relation to the distribution of marine animals. On the theory of descent with modification the great law of the long enduring but not immutable succession of the same types within the same areas is at once explained. For the inhabitants of each quarter of the world will obviously tend to leave in that quarter during the next succeeding period of time closely allied though in some degree modified descendants. If the inhabitants of one continent formally differed greatly from those of another continent so will their modified descendants still differ in nearly the same manner and degree. But after very long intervals of time and after great geographical changes permitting much inter-migration the febler will yield to the more dominant forms and there will be nothing immutable in the distribution of organic beings. It may be asked in ridicule whether I suppose that the megatherium and other allied huge monsters which formerly lived in South America have left behind them the sloth armadillo and anteater as their degenerate descendants. This cannot for an instant be admitted. These huge animals have become wholly extinct and have left no progeny. But in the caves of Brazil there are many extinct species which are closely allied in size and in all other characters to this species still living in South America. And some of these fossils may have been the actual progenitors between species. It must not be forgotten that on our theory all the species of the same genus are the descendants of some one species. So that if 6 genera each having 8 species be found in one geological formation and in a succeeding formation there would be 6 or other allied or representative genera each with the same number of species then we may conclude that generally only one species of each of the older genera has left modified descendants which constitute the new genera containing the several species. The other 7 species of each old genus having died out and left no progeny. Or, and this will be a far commoner case where 3 species and 2 or 3 alone of the 6 older genera will be the parents of the new genera. The other species and the other old genera having become utterly extinct. In failing orders with the genera and species decreasing in number as in the case of the Edentada of South America still fewer genera and species will leave modified Summary of the preceding and present chapters I have attempted to show that the geological record is extremely imperfect that only a small portion of the globe has been geologically explored with care. That only certain classes of organic beings having been largely preserved in a fossil state that the number both of specimens and of species preserved in our museums is absolutely as nothing compared with the number of generations which must have passed away even during a single formation. That owing to the subsidence being almost necessary for the accumulation of deposits rich in fossil species of many kinds and thick enough to outlast future degradation great intervals of time must have elapsed between most of our successive formations. That there has probably been more extinction during the periods of subsidence and more variation during the periods of elevation and during the latter the record will have been least perfectly kept that each single formation has not been continuously deposited that the duration of each formation is probably short compared with the average duration of specific forms. That migration has played an important part in the first appearance of new forms in any one area and formation. That widely ranging species are those which have varied most frequently and have often given rise to new species. That varieties have at first been local. And lastly, although each species must have passed through numerous transitional stages it is probable that the periods during which each underwent modification though many and long as measured by years have been short in comparison with the periods during which each remained in an unchanged condition. These causes taken conjointly will to a large extent explain why though we do find many links we do not find interminable varieties connecting together all extinct and existing forms by the finest graduated steps. It should also be constantly born in mind that any linking variety between two forms which might be found would be ranked unless the whole chain could be perfectly restored as a new and distinct species for it is not pretended that we have any sure criterion by which species and varieties can be discriminated. He who rejects this view of the imperfection of the geological record will rightly reject the whole theory for he may ask in vain where are the numberless transitional links which must formally have connected the closely allied or represented species found in the successive stages of the same great formation. He may disbelieve in the immense intervals of time which must have elapsed between our consecutive formations. He may overlook how important a part migration has played when the formations of any one great region as those of Europe are considered. He may urge the apparent but often falsely apparent sudden coming in of whole groups of species. He may ask where are the remains of those infinitely numerous organisms which must have existed long before the Cambrian system was deposited. We now know that at least one animal did then exist but I can answer this last question only by supposing that where our oceans now extend they have extended for an enormous period and where our oscillating continents now stand they have stood since the commencement of the Cambrian system but that long before that epic the world presented a widely different aspect in that the older continents formed of formations older than any known to us exist now only as remnants metamorphosed condition or lie still buried under the ocean. Passing from these difficulties the other great leading facts in paleontology agree admirably with the theory of descent with modification through variation and natural selection. We can thus understand how it is that new species come in slowly and successively how species of different classes necessarily change together or at the same rate or in the same degree yet in the long run that all undergo modification to some extent the extinction of old forms is the almost inevitable consequence of the production of new forms we can understand why when a species has once disappeared it never reappears. Groups of species increase in numbers slowly and endure for unequal periods of time for the process of modification is necessarily slow and depends on many complex contingencies. The dominant species belonging to large and dominant groups tend to leave many modified descendants which form new subgroups and groups. As these are formed the species of the less vigorous groups from their inferiority inherited from a common progenitor tend to become extinct together and to leave no modified offspring on the face of the earth. But the utter extinction of a whole group of species has sometimes been a slow process from the survival of a few descendants lingering in protected and isolated situations. When a group has once wholly disappeared it does not reappear for the link of generation has been broken. We can understand how it is that dominant forms which spread widely and yield the greatest number of varieties tend to people the world with allied but modified descendants and these will generally succeed in displacing the groups which are their inferiors in the struggle for existence. Hence after long intervals of time their productions of the world appear to have changed simultaneously. We can understand how it is that all the forms of life ancient and recent make together a few grand classes. We can understand from the continued tendency to divergence of character why the more ancient a form is the more it generally differs from those now living. Why ancient and extinct forms often tend to fill up gaps between existing forms sometimes blending two groups previously classed as distinct into one but more commonly bringing them only a little closer together. The more ancient a form is the more often it stands in some degree intermediate between groups now distinct for the more ancient a form is the more nearly it will be related to and consequently resemble the common progenitor of groups since become widely divergent. Extinct forms are seldom directly intermediate between existing forms but are intermediate only by a long and circuitous course through other extinct and different forms. We can clearly see why the organic remains of closely consecutive formations are closely allied for they are closely linked together by generation. We can clearly see why the remains of an intermediate formation are intermediate in character. The inhabitants of the world at each successive period in its history have beaten their predecessors in the race for life and are in so far higher in the scale and their structure has generally become more specialized and this may account for the common belief held by so many paleontologists that organization on the whole has progressed. Extinct and ancient animals resemble to a certain extent the embryos of the more recent animals belonging to the same classes and this wonderful fact receives a simple explanation according to our views. The succession of the same types of structure within the same areas during the later geological periods ceases to be mysterious and is intelligible on the principle of inheritance. If then the geological record be as imperfect as many believe and it may at least be asserted that the record cannot be proved to be much more perfect the main objections to the theory of natural selection are greatly diminished or disappear. On the other hand all the chief laws of paleontology plainly proclaim as it seems to me that species have been produced by ordinary generation old forms having been supplanted by new and improved forms of life. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information and to find out how you can volunteer please visit LibriVox.org Recorded by the LibriVox.org For more information and to find out how you can volunteer please visit LibriVox.org Recorded by LibriVox.org Recorded by Chip in Tampa, Florida on January 26, 2006 The Origin of Species by Means of Natural Selection or the Preservation of Favourite Races in the Struggle for Life Sixth London Edition by Charles Darwin Chapter 12 Geographical Distribution Present Distribution cannot be accounted for by differences in physical conditions importance of barriers affinity of the productions of the same continent centres of creation means of dispersal by changes of climate and the level of the land and by occasional means dispersal during the glacial period alternate glacial periods in the North and South In considering the distribution of organic beings over the face of the globe the first great fact which strikes us is that neither the similarity nor the dissimilarity of the inhabitants of various regions can be wholly accounted for by climatel or other physical conditions. Of late almost every author who has studied the subject has come to this conclusion. The case of America alone would almost suffice to prove its truth for if we exclude the Arctic and northern temperate parts all authors agree that one of the most fundamental divisions in geographical distribution is between the new and old worlds. Yet if we travel over the vast American continent from the central parts of the United States to its extreme southern point we meet with the most diversified conditions humid districts arid deserts earthy mountains grassy plains forests, marshes, lakes and great rivers under almost every temperature. There is hardly a climate or condition in the old world which cannot be paralleled in the new at least so closely as the same species generally require. No doubt small areas can be pointed out in the old world hotter than any in the new world but these are not inhabited from that of the surrounding districts for it is rare to find a group of organisms confined to a small area in which the conditions are peculiar in only a slight degree notwithstanding this general parallelism of the conditions of the old and new worlds how widely different are their living productions. In the southern hemisphere if we compare large tracts of land in Australia, South Africa between latitudes 25 and 35 degrees we shall find parts extremely similar in all their conditions yet it would not be possible to point out three faunas and flora more utterly dissimilar. Or again we may compare the productions of South America south of latitude 35 degrees with those north of 25 degrees which consequently are separated by a space of 10 degrees of latitude and are exposed to considerably different conditions yet they are incomparably more closely related to each other than they are to the productions of Australia or Africa under nearly the same climate Analogous facts could be given with respect to the inhabitants of the sea. A second great find which strikes us in our general review are the barriers of any kind or obstacles to free migration are related in a close and important manner to the differences between productions of various regions. We see this in the great difference in nearly all the terrestrial productions of the old and new worlds accepting in the northern parts where the land almost joins and where under a slightly different climate there might have been free migration in temperate forms as there now is for these strictly arctic productions. We see the same fact in the great difference between the inhabitants of Australia, Africa and South America under the same latitude for these countries are almost as isolated from each other as is possible. On each continent also we see the same fact for on the opposite sides of lofty and continuous mountain ranges and of great deserts and even of large rivers we find different productions though as mountain chains, deserts etc. are not as impassable or likely to have endured so long as the oceans separating the continents the differences are very inferior in degree to those characteristic of distinct continents. Turning to the sea we find the same law the marine inhabitants of the eastern and western shores of South America are very distinct with extremely few shells, crustacea or Icanodermata in common but Dr. Gunther has recently shown that about 30% of the fishes are the same on the opposite sides of the Ismus of Panama and this fact has led naturalists to believe that the Ismus was formerly open. Westward of the shores of America a wide space of open ocean extends with not an island as a halting place for emigrants here we have a barrier of another kind and as soon as this is passed we meet in the eastern islands of the Pacific with another totally distinct fauna so that three marine faunas range northward and southward in parallel lines not far from each other under corresponding climate separated from each other by impassable barriers either of land or open sea they are almost wholly distinct on the other hand proceeding still further westward from the eastern islands of the tropical parts of the Pacific we enter no impassable barriers and we have innumerable islands as halting places or continuous coasts until after traveling over a hemisphere we come to the shores of Africa and over this vast space we meet with no well-defined and distinct marine faunas although so few marine animals are common to the above-named three approximate faunas of eastern and western America and the eastern Pacific islands yet many fishes range from the Pacific into the Indian Ocean and many shells are common to the eastern islands of the Pacific and the eastern shores of Africa on almost exactly opposite meridians of longitude a third great fact partly included in the foregoing statement is the affinity of the productions of the same continent though the species themselves are distinct at different points and stations it is a law of the widest generality and every continent offers innumerable instances nevertheless the naturalist in traveling for instance from north to south never fails to be struck by the manner in which successive groups of beings specifically distinct though nearly related replace each other he hears from closely allied yet distinct kinds of birds notes nearly similar and sees their nests similarly constructed but not quite alike with eggs colored in nearly the same manner the planes near the straits of Magellan are inhabited by one species of Rea, American ostrich and northward the planes of Laplata by another species of the same genus and not by a true ostrich or emu like those inhabiting Africa and Australia under the same latitude on these same planes of Laplata we see the Aguti and Biscacha animals having nearly the same habits as our hairs and rabbits and belonging to the same order of rodents but they plainly display an American type of structure we ascend the lofty peaks of the Cordillera and find an alpine species of Biscacha we look to the waters and we do not find the beaver or muskrat but the coipu and the capybara rodents of the South American type innumerable other instances could be given if we look to the islands off the American shore however much they may differ in geological structure the inhabitants are essentially American though they may be all peculiar species we may look back to past ages as shown in the last chapter and we find American types then prevailing on the American continent and in the American seas we see in these facts some deep organic bond throughout space and time over the same areas of land and water independently of physical conditions the naturalist must be dull who is not led to inquire what this bond is the bond is simply inheritance that cause which alone as far as we positively know produces organisms quite like each other or as we see in the case of varieties nearly alike the dissimilarity of the inhabitants of different regions may be attributed to modification through variation and natural selection and probably in a subordinate degree to the definite influence of different physical conditions the degrees of dissimilarity will depend on the migration of the more dominant forms of life to one region to another having been more or less effectively prevented at periods more or less remote on the nature and number of former immigrants and on the action of the inhabitants on each other in leading to the preservation of different modifications the relation of organism to organism in the struggle for life being as I have already often remarked the most important of all relations thus the high importance of barriers comes into play by checking migration as does time for the slow process of modification through natural selection widely ranging species abounding in individuals which have already triumphed over many competitors in their own widely extended homes will now have the best chance of seizing on new places when they spread out into new countries in their new homes they will be exposed to new conditions and will frequently undergo further modification and improvement and thus they will become still further victorious and will produce groups of modified descendants on this principle of inheritance with modification we can understand how it is that sections of genera whole genera and even families are confined to the same areas as is so commonly and notoriously the case there is no evidence as was remarked in the last chapter of the existence of any law of necessary development as the variability of each species is an independent property and will be taken advantage of by natural selection only so far as it profits each individual in its complex struggle for life so the amount of modification species will be no uniform quantity if a number of species after having long competed with each other in their old home were to migrate in a body to a new and afterwards isolated country they would be little liable to modification for neither migration nor isolation in themselves affect anything these principles come into play only by bringing organisms into new relations with each other and in a lesser degree with the surrounding physical conditions as we have seen in the last chapter that some forms have retained nearly the same character from an enormously remote geological period so certain species have migrated over vast spaces and have not become greatly or at all modified according to these views it is obvious that several species of the same genus though inhabiting the most distant quarters of the world must originally have proceeded from the same source as they are descended from the same progenitor in the case of those species which have undergone during whole geological periods little modification there is not much difficulty in believing that they have migrated from the same region for during the vast geographical and climatical changes which have been since ancient times almost any amount of migration is possible but in many other cases in which we have reason to believe that the species of a genus have been produced within comparatively recent times there is great difficulty on this head it is also obvious that the individuals of the same species though now inhabiting different and isolated regions must have proceeded from one spot where their parents were first produced for as has been explained it is incredible that individuals identically the same should have been produced from parents specifically distinct single centers of supposed creation we are thus brought to the question which has been largely discussed by naturalists namely whether species have been created at one or more points on the earth's surface undoubtedly there are many cases of extreme difficulty in understanding how the same species could possibly have migrated from some one point to the several distant and isolated points were now found nevertheless the simplicity of the view that each species was first produced within a single region captivates the mind he who rejects it rejects the better cause of ordinary generation with subsequent migration and calls in the agency of a miracle it is universally admitted that in most cases the area inhabited by a species is continuous and that when a plant or animal inhabits two points so distant from each other or with an interval of such a nature that the space could not have been easily passed over by migration the fact is given as something remarkable and exceptional the incapacity of migrating across a wide sea is more clear in the case of terrestrial mammals than perhaps with any other organic beings and accordingly we find no inexplicable instances of the same mammals inhabiting distant points of the world no geologist feels any difficulty in Great Britain possessing the same quadrupeds with the rest of Europe for they were no doubt once united but if the same species can be produced at two separate points why do we not find a single mammal common to Europe and Australia or South America the conditions of life are nearly the same so that a multitude of European animals and plants have become naturalized in America and Australia and some of the aboriginal plants are identically the same at these different points on the northern and southern hemispheres the answer as I believe is that mammals have not been able to migrate whereas some plants from their very means of dispersal have migrated across the wide and broken interspaces the great and striking influence of barriers of all kinds is intelligible only on the view that the great majority of species have been produced on one side and have not been able to migrate on the opposite side some few families many sub-families very many genera and still greater numbers of sections of genera are confined to a single region and it has been observed by several naturalists that the most natural genera or those genera in which the species are most closely related to each other are generally confined to that their range is continuous what a strange anomaly it would be if a directly opposite rule were to prevail when we were to go down one step lower in the series namely to the individuals of that same species and these had not been at least at first confined to some one region hence it seems to me as it has to many other naturalists that the view of each species having been produced in one area alone and having subsequently migrated from that area as far as its powers of migration and substance under past and present conditions permitted it is most probable undoubtedly many cases occur in which we cannot explain how the same species could have passed from one point to the other but the geographical and climatical changes which have certainly occurred within recent geological times must have rendered discontinuous the formally continuous range of many species so that we are reduced to consider whether the exceptions to continuity of range are so numerous and of so grave a nature that we ought to give up the belief rendered probable by general considerations that each species has been produced within one area and separated then as far as it could it would be hopelessly tedious to discuss all the exceptional cases of the same species now living at distant and separated points nor do I for a moment pretend that any explanation could be offered of many instances but after some preliminary remarks I will discuss a few of the most striking classes of facts namely the existence of the same species on the summits of distant mountain ranges and at distant points in the arctic and Antarctic regions and secondly in the following chapter the wide distribution of fresh water productions and thirdly the occurrence of the same terrestrial species on islands and on the nearest mainland though separated by hundreds of miles of open sea if the existence of the same species at distant and isolated points of the Earth's surface can in many instances be explained on the view of each species having migrated from a single birthplace then considering our ignorance with respect to former climatical and geographical changes and to the various occasional means of transport the belief that a single birthplace is the law seems to me incomparably the safest in discussing this subject we shall be enabled at the same time to consider a point equally important for us namely whether the several species of a genus which must on our theory all be descended from a common progenitor can have migrated undergoing modification during their migration from some one area if when most of the species inhabiting one region are different from those in another region though closely alive to them it can be shown that migration from one region to the other has probably occurred at some former period our general view will be much strengthened for the explanation is obvious on the principle of descent with modification a volcanic island for instance up heaved and formed at the distance of a few hundreds of miles from a continent probably would receive from it in the course of time a few colonists and their descendants though modified would still be related by inheritance to the inhabitants of that continent cases of this nature are common and are as we shall hear after see inexplicable on the theory of independent creation this view of the relation of the species of one region to those of another does not differ much from that advanced by Mr. Wallace who concludes that every species has come into existence coincident both in space and time with a pre-existing closely allied species and it is now well known that he attributes this coincidence to descent with modification the question of single and multiple centers of creation differs from another though allied question namely whether all the individuals of the same species are descended from a single pair or single hermaphrodite or whether as some authors suppose from many individuals simultaneously created with organic beings which never intercross if such exist such species must be descended from a succession of modified varieties that have supplanted each other but have never blended with other individuals or varieties of the same species so that at each successive stage of modification all the individuals of the same form will be descended from a single parent but in the great majority of cases namely with all organisms which habitually unite for each birth or which occasionally intercross the individuals of the same species inhabiting the same area will be kept nearly uniform by intercrossing so that many individuals will go on simultaneously changing and the whole amount of modification at each stage will not be due to descent from a single parent to illustrate what I mean our English race horses differ from the horses of every other breed but they do not owe their difference and superiority to descent from any single pair but to continued care in the selecting and training of many individuals during each generation before discussing the three classes of facts for which I have selected as presenting the greatest amount of difficulty on the theory of single centres of creation I must say a few words on the means of dispersal means of dispersal Sir C. Lyell and other authors have ably treated this subject and give here only the briefest abstract of the more important facts change of climate must have had a powerful influence on migration a region now impassable to certain organisms from the nature of its climate might have been a high road for migration when the climate was different I shall however presently have to discuss this branch of the subject in some detail changes of level in the land are very influential a narrow isthmus now separates two marine faunas submerge it or let it formerly have been submerged and the two faunas will now blend together or may formerly have blended where the sea now extends land may at a former period have connected islands or possibly even continents together and thus have allowed terrestrial productions to pass from no geologist disputes that great mutations of level have occurred within the period of existing organisms Edward Forbes insisted that all the islands in the Atlantic must have been recently connected with Europe or Africa and Europe likewise with America other authors have thus hypothetically bridged over every ocean and united almost every island with some mainland if indeed the arguments used by Forbes are to be trusted it must be admitted that scarcely a single island exists which has not recently been united to some continent this view cuts the Gordian knot of the dispersal of the same species to the most distant points and removes many a difficulty but to the best of my judgment we are not authorized in admitting such enormous geographical changes within the period of existing species it seems to me that we have abundant evidence of great oscillations of the level of land or sea but not of such vast changes in the position and extension of our continents as to have united them within the recent period to each other and to the several intervening oceanic islands I freely admit that the former existence of many islands now buried beneath the sea which may have served as halting places for plants and for many animals during their migration in the coral producing oceans such sunken islands are now marked by rings of coral or atolls standing over them whenever it is fully admitted as it will someday be that each species has proceeded from a single birthplace and when in the course of time something definite about the means of distribution we shall be enabled to speculate with security on the former extension of the land but I do not believe that it will ever be proved that within the recent period most of our continents which now stand quite separate have been continuously or almost continuously united with each other and with the many existing oceanic islands several facts in distributions such as the great difference in the marine faunas on the opposite sides of almost every continent the close relation with the tertiary inhabitants of several lands and even seas to their present inhabitants the degree of affinity between the mammals inhabiting islands with those of the nearest continent being in part determined as we shall hereafter see by the depth of the intervening ocean these and other such facts are opposed to the admission of such prodigious geographical revolutions within the recent period as are necessary on the view advanced by Forbes and admitted by his followers the nature and relative proportions of the inhabitants of oceanic islands are likewise opposed to the belief of their former continuity of continents nor does the almost universally volcanic composition of such islands favor the admission that they were the wrecks of sunken continents if they had originally existed as continental mountain ranges some at least of the islands would have been formed like other mountain summits of granite metamorphic shifts, old fossiliferous and other rocks instead of consisting of mere piles of volcanic matter I must now say a few words on what are called accidental means but which more properly should be called occasional means of distribution I shall here confine myself to plants in botanical works this or that plant is often stated to be ill adapted for wide dissemination but the greater or less facilities for transport across the sea may be said to be almost wholly unknown until I tried with Mr. Berkeley's aid a few experiments it was not even known how far seeds could resist the injurious action of seawater to my surprise I found out that of the 87 kinds 64 germinated after an immersion of 28 days and a few survived an immersion of 137 days it deserves notice that certain orders were far more injured than others 9 liguminose were tried with one exception they resisted the salt water badly 7 species of the allied orders hydrocephaly and polymysiae were all killed by a month's immersion for convenience sake I chiefly tried small seeds without the capsules or fruit and as all of these sank in a few days they could not have floated across wide spaces of the sea whether or not they were injured by salt water afterwards I tried some larger fruits capsules etc and some of these floated for a long time it is well known what a difference there is in the buoyancy of green and seasoned timber and it occurred to me that floods would often wash into the sea dried plants or branches with seed capsules or fruit attached to them hence I was led to dry the stems and branches of 94 plants of fruit and to place them on seawater the majority sank quickly but some which whilst green floated for a very short time when dried floated much longer for instance ripe hazelnuts sank immediately but when dried they floated for 90 days and afterwards when planted germinated an asparagus plant with ripe berries floated for 23 days when dried it floated for 85 days and the seeds afterwards germinated the ripe seeds of heliosodium sank in 2 days when they dried they floated for above 90 days and afterwards germinated altogether out of 94 dried plants 18 floated for above 28 days and some of the 18 floated for a very much longer period so that as 64 of 87 kinds of seeds germinated after an immersion of 28 days and as 18 of 94 distinct species with ripe fruit but not all the same species as in the foregoing experiment floated after being dried for above 28 days we may conclude that as far as anything can be inferred from these scanty facts that the seeds of 14 of 100 kinds of plants in one country might be floated by sea currents during 28 days and would retain their power of germination in Johnson's physical atlas the average rate of these several Atlantic currents is 33 miles per diem some currents running at the rate of 60 miles per diem on this average the seeds of 14 of 100 plants belonging to one country might be floated across 24 miles of sea to another country and when stranded if blown inland by a gale to a favorable spot would germinate subsequently to my experiments Mr. Martens tried similar ones but in a much better manner for he placed the seeds in a box in the actual sea so they were alternately wet and exposed to the air like really floating plants he tried 98 seeds previously different from mine but he chose many large fruits and likewise seeds from plants which live near the sea and this would have favored both the average length of their floatation and their resistance to the injurious action of the salt water on the other hand he did not previously dry the plants or branches with the fruit and this as we have seen could have caused some of them to have floated much longer the result was that 18 of 98 of his seeds of different kinds floated for 42 days and were then capable of germination but I do not doubt that plants exposed to the waves would float for a less time than those protected from violent movement as in our experiments therefore it would perhaps be safer to assume that the seeds of about 10 of 100 plants of a flora after having been dried could be floated across a space of sea 900 miles in width and would then germinate the fact of the larger fruits often floating longer than the small is interesting as plants with large seeds or fruit which as alfons de candol has shown generally have restricted ranges could hardly be transported by any other means seeds may be occasionally transported in another manner drift timber is thrown up on most islands even on those in the midst of the widest oceans and the natives of the coral islands in the pacific procure stones for their tools solely from the roots of drifted trees these stones being a valuable royal tax I find that when irregularly shaped stones are embedded in the roots of trees the small parcels of earth are very frequently enclosed in their interstices behind them so perfectly that not a particle could be washed away during the longest transport out of one small portion of earth thus completely enclosed by the roots of an oak about 50 years old three dichotolidinous plants germinated I am certain of the accuracy of this observation again I can show that the carcasses of birds when floating on the sea sometimes escape being immediately devoured and many kinds of seeds in the crops of floating birds long retain their vitality peas and vetches for instance are killed by even a few days immersion in seawater but some taken out of the crop of the pigeon which has floated on artificial seawater for 30 days to my surprise nearly all of them are pollinated living birds can hardly fail to be a highly effective agent in the transportation of seeds I could give many facts showing how frequently birds of many kinds are blown by gales to vast distances across the ocean we may safely assume that under such circumstances their rate of flight would often be 35 miles an hour and some authors have given a far higher estimate I have never seen an instance of nutritious seeds passing through the intestines of a bird but hard seeds of a fruit pass uninjured through even the digestive organs of a turkey in the course of two months I picked up in my garden 12 kinds of seeds out of the excrement of small birds and these seemed perfect and some of them which were tried germinated but the following fact is more important the crops of birds do not secrete gastric juices and do not, as I know by trial injure in the least the germination of seeds now after a bird has found and devoured a large supply of food it is positively asserted that all the grains do not pass into the gizzard for 12 or even 18 hours a bird in this interval of flight might easily be blown by the distance of 500 miles and hawks are known to look out for tired birds and the contents of their torn crops might thus readily get scattered some hawks and owls bolt their prey whole and after an interval of from 12 to 20 hours disgorge pellets which as I know from experiments made in the zoological gardens include seeds capable of germination some seeds of the oat, wheat, millet cannery, hemp clover and beet germinated after having been from 12 to 21 hours in the stomachs of different birds of prey and two seeds of beet grew after having been thus retained for 2 days and 14 hours freshwater fish I find eat seeds of many land and water plants fish are frequently devoured by birds and thus the seeds might be transported from place to place I forced many kinds of seeds into the stomachs of dead fish and then gave their bodies to fishing eagles storks and pelicans these birds after an interval of many hours either rejected the seeds in pellets or passed them in their excrement and several of these seeds retained the power of germination certain seeds however nearly always killed by this process locusts are sometimes blown great distances from land I myself caught one 370 miles from the coast of Africa and have heard of others caught at greater distances the Reverend R. T. Low informed Sir C. Lyell that in November of 1844 swarms of locusts visited the island of Madeira they were in countless numbers as thick as flakes of snow in the heaviest snowstorm and extended upward as far as could be seen with the telescope during two or three days they slowly careered round and round in an immense ellipse at least five or six miles in diameter and at night alighted on the taller trees which were completely coated with them they then disappeared over the sea as suddenly as they had appeared not since visited the island now in parts of Natal it is believed by some farmers though on insufficient evidence that injurious seeds are introduced into their grassland in the dung left by the great flights of locusts which often visited that country in consequence of this belief Mr. Wiel sent me in a letter a small packet of the dried pellets out of which I extracted under the microscope several seeds and raised from them seven grass plants belonging to two species of two genera hence a swarm of locusts such as that which visited Madeira might readily be the means of introducing several kinds of plants to an island lying far from the mainland although the beaks and feet of birds are generally clean earth sometimes adheres to them in one case I removed sixty-one grains in another case twenty-two grains of dry agrelatious earth from the foot of a partridge and in the earth there was a pebble as large as the seed of a vetch here is a better case the leg of a woodcock was sent to me by a friend with a little cake of dry earth attached to the shank weighing only nine grains and this contained a seed toadrush which germinated and flowered Mr. Sway's land of Brighton, who during the last forty years has paid close attention to our migratory birds informs me that he has often shot wag-tails motziliy and windchats on their first arrival upon our shores before they had alighted and has several times noticed attached to their feet many facts could be given showing how generally soil is charged with seeds for instance Professor Newton sent me the leg of a red-legged partridge Cacabas Rufa which had been wounded and could not fly with a ball of hard earth adhering to it and weighing six and a half ounces the earth had been kept for three years but when broken and littered and placed under a bell-glass no less than eighty-two plants sprung from it these consisted of twelve monocotletons including the common oat and at least one kind of grass and of seventy dichotletons which consisted judging from the young leaves of at least three distinct species with such facts before us can we doubt that the many birds which are annually blown by gales across great spaces of ocean and which annually migrate for instance the millions of quails across the Mediterranean must occasionally transport a few seeds embedded in dirt adhering to their feet or beaks but I shall have to recur to this subject as icebergs are known to be sometimes loaded with dirt and stones and have even carried brushwood bones and the nest of a land bird it can hardly be doubted that they must occasionally as suggested by Lyell have transported seeds from one part to another of the Arctic and Antarctic regions and during the glacial period from one part of the now temperate regions to another in the Azores from the large number of plants common to Europe in comparison with the species of the other islands of the Atlantic which stand nearer to the mainland as remarked by Mr. H. C. Watson from their somewhat northern character in comparison with the latitude I suspected that these islands had been partly stocked by ice-born seeds during the glacial epoch at my request Sir C. Lyell wrote to Mr. Hartung to inquire whether he had observed erratic boulders on these islands and he answered that he had found large fragments of granite of the rocks which do not occur in the archipelago hence we may safely infer that the icebergs formerly landed their rocky burdens on the shores of these mid-ocean islands and it is at least possible that they may have brought the seeds of northern plants considering that these several means of transport and that other means which without doubt remain to be discovered have been mentioned year after year for tens of thousands of years it would I think be a marvellous fact if many plants had not thus been widely dispersed these means of transport are sometimes called accidental but this is not strictly correct the currents of the sea are not accidental nor is the direction of prevalent gales of wind it should be observed that scarcely any means of transport would carry suffice for very great distances for seeds do not retain their vitality when exposed for a great length of time to the action of sea water nor could they be long carried in the crops or intestines of birds these means however would suffice for occasional transport across tracts of seas some hundreds of miles in breadth or from island to island or from a continent to a neighboring island but not from one distant continent to another the florals of distant continents would not by such means become mingled but would remain as distinct as they now are the currents from their course would never bring seeds from North America to Britain although they might and do bring seeds from the West Indies to our western shores where if not killed by their very long immersion in salt water they could not endure our climate almost every year one or two land birds are blown across the whole Atlantic Ocean from North America to the western shores of Ireland and England but seeds could be transported by these rare wanderers only by one means namely by dirt adhering to their feet or beaks which is in itself a rare accident even in this case how small would be the chance of a seed falling on favorable soil and coming to maturity but it would be a great error to argue that because a well-stocked island like Great Britain has not as far as is known and it would be very difficult to prove this received within the last few centuries through occasional means of transport immigrants from Europe or any other continent that a poorly stocked island though standing more remote from the mainland would not receive colonists by similar means out of a hundred kinds of seeds or animals transported to an island even if far less well stocked than Britain perhaps not more than one would be so well fitted to its new home as to become naturalized but this is no valid argument against what would be affected by occasional means of transport during a long lapse of geologic time whilst the island was being upheaved and before it had become fully stocked with inhabitants on almost bare land with few or no destructive insects or birds living there nearly every seed which chanced to arrive if fitted for the climate would germinate and survive So ends the first section of Chapter 12 The Origin of Species by Charles Darwin