Natural Selection &Amp; Tropical Nature

Preface

The present volume consists mainly of a reprint of two volumes of essays — Contributions to the Theory of Natural Selection , which appeared in 1870, with a second edition in 1871, and has now been many years out of print; and, Tropical Nature and Other Essays, which appeared in 1878.

In preparing a new edition of these works to appoar as a single volume I have thought it advisable to omit two essays—that on “ The Malayan Papilionidao ” as being too technical for general readers, and that on “ The Distribution of Animals as indicating Geographical Changes/’ which con¬ tains nothing that is not more fully treated in my other works. Another essay — “By - Paths in the Domain of Biology ”—has also been partly omitted, one portion of it forming a short chapter on “ The Antiquity and Origin of Man,” while another portion has been incorporated in the chapter on “ The Colours of Animals and Sexual Selection.” More than compensating for these omissions arc two now chapters—“ The Antiquity of Man in North America ” and “ The Debt of Science to Darwin.”

Many corrections and some important additions have boon made to the text, the chief of which are indicated in the table given below ; and to facilitate reference the two original works have separate headings, and form Parts L and II. of the present volume.

VI

PREFACE

Alterations in the Second Edition of Contributions, etc.

1st Ed.

2d Ed.

Present

Volume.

Additional facts as to birds acquiring the song of other species ....

Mr. Spruce’s remarks on young birds pairing with old ....

Pouchet’s observations on a change in the nests of swallows ....

omitted

_

Passage omitted about nest of Golden

Crested Warbler, which had been in¬ serted on Rennie’s authority, but lias not been confirmed by any later ob¬ servers.

Dailies Barrington, on importance of pro¬ tection to the female bird .

Note A.

Note B.

ADDITIONAL MATTER IN THE PRESENT VOLUME. Natuiial Selection.

PAGES

Additional facts by Leroy, Spalding, Lowne, ami Dixon on the

Nest-Building and other Instincts of Birds . . . 108-112

Dr. Abbott on Nesting of Baltimore Oriole . . . 114

Professor Jeittelcs and Mr. Henry Reeks on Alterations in Mode of Nest-Building . . . . . . 115

Tropical Nature.

Note on Dr. Shufeldt’s Investigations into the Affinities of Swifts and Humming-Birds ..... 337

The Antiquity of Man in North America.

(Additional Chapter) ...... 433-419

Tiie Debt of Science to Darwin.

(Additional Chapter) ...... 450-475

Paiikstone, T) orset, March 1891.

NATUBAL SELECTION

I. On the Law which has Regulated the Introduction of

New Species

Geographical Distribution dependent on Geologic Changes—A Law deduced from well-known Geographical and Geological facts—The Form of a true system of Classification determined by this Law—Geographical Distribution of Organisms—Geological Distribution of the Forms of Life—High Organisation of very ancient Animals consistent with this Law—Objections to Forbes’s Theory of Polarity—Rudimentary Organs—Conclusion ..... Pages 3-19

II. On the Tendency of Varieties to Depart Indefinitely

from the Original Type

Introductory Note—Instability of Varieties supposed to prove the per¬ manent distinctness of Species—The Struggle for Existence—The Law of Population of Species—The Abundance or Rarity of a Species dependent upon its more or less perfect Adaptation to the Conditions of Existence—Useful Variations will tend to Increase ; useless or hurtful Variations to Diminish—Superior Varieties will ultimately Extirpate the Original Species—The Partial Reversion of Domesti¬ cated Varieties explained—Lamarck’s Hypothesis very different from that now advanced—Conclusion . . . .20-33

III. Mimicry, and other Protective Resemblances among

Animals

Test of true and false Theories—Importance of the Principle of Utility —Popular Theories of Colour in Animals—Importance of Conceal¬ ment as Influencing Colour—Special Modifications of Colour—Theory viii of Protective Colouring—Objection that Colour, as being dangerous, should not exist in Nature—Mimicry—Mimicry amoug Lepidoptera —Lepidoptera mimicking other Insects—Mimicry among Beetles— Beetles mimicking other Insects—Insects mimicking Species of other Orders—Cases of Mimicry among the Vertebrata—Mimicry among Snakes—Mimicry among Birds—Mimicry among Mammals—Objec¬ tions to Mr. Bates’s Theory of Mimicry—Mimicry by Female Insects only—Cause of the dull Colours of Female Birds—Use of the gaudy Colours of many Caterpillars—Summary—General deductions as to Colour in Nature—Conclusion.... Pages 34-90

IV. On Instinct in Man and Animals

How Instinct may be best Studied—Definition of Instinct—Does Man possess Instincts ?—How Indians travel through unknown and track¬ less Forests ...... 91-97

V. The Philosophy of Birds’ Nests

Instinct or Reason in the Construction of Birds’ Nests—Do Men build by Reason or by Imitation ?—Why does each Bird build a peculiar kind of Nest ?—How do young Birds learn to build their first Nest ? Do Birds sing by Instinct or by Imitation ?—How young Birds may learn to build Nests—The Skill exhibited in Nest-building Ex¬ aggerated—Man’s Works mainly Imitative—Birds do Alter and Improve their Nests when altered Conditions require it—Conclusion

98-117

VI. A Theory of Birds’ Nests

Changed Conditions and persistent Habits as influencing Nidification— Classification of Nests—Sexual differences of Colour in Birds—The Law which connects the Colours of Female Birds with the mode of Nidification—What the Facts Teach us—Colour more variable than Structure or Habits, and therefore the Character which has generally been Modified—Exceptional cases confirmatory of the above Explana¬ tion—Real or apparent exceptions to the Law stated at page 124— Various modes of Protection of Animals—Females of some groups require and obtain more Protection than the Males—Conclusion

118-140

VII. Creation by Law

Laws from which the Origin of Species may he deduced—Mr. Darwin’s Metaphors liable to Misconception—A case of Orchid-structure ex-

IX plained by Natural Selection—Adaptation brought about by General Laws—Beauty in Nature—How New Forms are produced by Varia¬ tion and Selection—The Objection that there are Limits to Variation —Objection to the Argument from Classification—The Times on Natural Selection—Intermediate or generalised Forms of Extinct Animals an indication of Transmutation or Development—Conclu¬ sion—A Demonstration of the Origin of Species by Natural Selection

VIII. The Development op Human Eaces under the Law op Natural Selection

Wide differences of Opinion as to Man’s Origin—Outline of the Theory of Natural Selection—Different Effects of Natural Selection on Animals and on Man—Influence of External Nature in the develop¬ ment of the Human Mind—Extinction of Lower Races—The Origin of the Races of Man—The Bearing of these Views on the Antiquity of Man—Their Bearing on the Dignity and Supremacy of Man— Their Bearing on the future Development of Man—Summary—Con¬ clusion ....... 167-185

IX. The Limits op Natural Selection as Applied to Man

What Natural Selection can Not do—The Brain of the Savage shown to bo Larger than he Needs it to be—Size of Brain an important Element of Mental Power—Comparison of the Brains of Alan and of Anthropoid Apes—Range of Intellectual Power in Man—Intellect of Savages and of Animals compared—The use of the Hairy Covering of Mammalia—The Constant Absence of Hair from certain parts of Man’s body a remarkable Phenomenon—Savage Man feels the want of this Hairy Covering—Man’s Naked Skin could not have been pro¬ duced by Natural Selection—Feet and Hands of Man considered as Difficulties on the Theory of Natural Selection—The Voice of Man— —The Origin of some of Man’s Mental Faculties, by the preservation of Useful Variations, not possible—Difficulty as to the Origin of the Moral Sense—Summary of the Argument as to the Insufficiency of Natural Selection to account for the* Development of Man—The Origin of Consciousness—The Nature of Matter—Matter is Force —All Force is probably Will-force—Conclusion . . 186-214

X

TROPICAL NATURE AND OTHER ESSAYS

I. The Climate and Physical Aspects op the Equatorial Zone

The three Climatal Zones of the Earth—Temperature of the Equatorial Zone—Causes of the Uniform High Temperature near the Equator— Influence of the Heat of the Soil—Influence of the Aqueous Yapour of the Atmosphere—Influence of "Winds on the Temperature of the Equator—Heat due to the Condensation of Atmospheric Vapour— General Eeatnres of the Equatorial Climate—Uniformity of the Equatorial Climate in all Parts of the Globe—Effects of Vegetation on Climate—Short Twilight of the Equatorial Zone—The Aspect of the Equatorial Heavens—Intensity of Meteorological Phenomena at the Equator—Concluding Remarks . . Pages 217-237

II. Equatorial Vegetation

The Equatorial Eorest-belt and its Causes—General Features of the Equa¬ torial Forests—Characteristics of the Larger Forest-Trees—Flowering Trunks and their Probable Cause—Uses of Equatorial Forest-trees— The Climbing Plants of the Equatorial Forests—Palms—Uses of Palm-trees and their Products—Ferns—Ginger-worts and Wild Bananas— Arums—Screw-pines—Orchids—Bamboos—Uses ofthe Bamboo—Man¬ groves—Sensitive Plants—Comparative Scarcity of Flowers—Con¬ cluding Remarks on Tropical Vegetation . . . 238-269

III. Animal Life in the Tropical Forests

Difficulties of the Subject—General Aspect of the Animal Life of Equa¬ torial Forests—Diurnal Lepidoptera or Butterflies—Peculiar Habits of Tropical Butterflies—Aryfcs, Wasps, and Bees—Ants—Special Rela¬ tions between Ants and Vegetation—Wasps and Bees—Orthoptera and other Insects—Beetles—Wingless Insects—General Observations on Tropical Insects—Birds—Parrots—Pigeons—Picarise—Cuckoos— Trogons, Barbets, Toucans, and Hornbills—Passeres—Reptiles and Amphibia : Lizards—Snakes—Frogs and Toads—Mammalia : Mon¬ keys—Bats—Summary of the Aspects of Animal Life in the Tropics

270-311 xi

IY. Htjmming-Birds : As Illustrating the Luxuriance of Tropical Nature

Structure—Colours and Ornaments—Descriptive Names—The Motions and Habits of Humming-birds—Display of Ornaments by the Male—Food —Nests—Geographical Distribution and Yariation—Humming-birds of Juan Fernandez as illustrating Yariation and Natural Selection— The Relations and Affinities of Humming-birds—How to Determine Doubtful Affinities—Resemblances of Swifts and Humming-birds— Differences between Sun-birds and Humming-birds—Conclusion

Y. The Colours of Animals and Sexual Selection

General Phenomena of Colour in the Organic World—Theory of Heat and Light as producing Colour—Changes of Colour in Animals produced by Coloured Light—Classification of Organic Colours—Protective Colours—Warning Colours—Sexual Colours—Normal Colours—The Nature of Colour—How Animal Colours are produced—Colour a Normal Product of Organisation—Theory of Protective Colours— Theory of Warning Colours—Imitative Warning Colours—The Theory of Mimicry—Theory of Sexual Colours—Colour as a means of Recognition—Colour proportionate to Integumentary Development— Selection by Females not a cause of Colour—Probable use of the Horns of Beetles—Cause of the greater Brilliancy of some Female Insects — Origin of the Ornamental Plumage of Male Birds — Theory of the Display of Ornaments by Males—Natural Selection as neutralising Sexual Selection—Greater Brilliancy of some Female Birds—Colour - development as illustrated by Humming-birds — —Theory of Normal Colours—Local causes of Colour-development— The influence of Locality on Colour in Butterflies and birds—Sense-perception influenced by Colour of the Integuments—Summary on Colour-development in Animals .... 338-394

YI. The Colours of Plants and the Origin of the Colour-Sense

Source of Colouring Matter in Plants—Protective Coloration and Mimicry in Plants—Attractive Colours of Fruits—Protective Colours of Fruits —Attractive Colours of Flowers—Attractive Odours in Flowers— Attractive Grouping of Flowers—Why Alpine Flowers are so Beauti¬ ful—Why Allied Species of Flowers differ in Size and Beauty- Absence of Colour in Wind-fertilised Flowers—The same Theory of Colour applicable to Animals and Plants—Relation of the Colours

XU of Elowers and their Geographical Distribution — Recent Views as to Direct Action of Light on the Colours of Flowers and Emits— Concluding Remarks on the Importance of Colour in the Organic World—On the Origin of the Colour-sense : Supposed Increase of Colour-perception within the Historical Period—Concluding Remarks on the Colour-sense ..... Pages 395-415

VII. The Antiquity* and Origin op Man

Indications of Man’s extreme Antiquity—Antiquity of Intellectual Man —Sculptures on Easter Island—North American Earthworks—The Great Pyramid—Conclusion .... 416-432

VIII. The Antiquity op Man in North America

Ancient Shell Mounds—Man Coeval with Extinct Mammalia—Man in the Glacial Period—Palaeolithic Implements in North America—The Auriferous Gravels of California—Fossil Remains under the Ancient Lava Beds—Works of Art in the Auriferous Gravels—Human Remains in the Auriferons Gravels—Concluding Remarks on the Antiquity of Man .... . . 433*449

IX. The Debt op Science to Darwin

The Century before Darwin—The Voyage of the Beagle—The, Journal of Researches —Studies of Domestic Animals—Studies of Cultivated and Wild Plants—Researches on the Cowslip, Primrose, and Loose¬ strife—The Struggle for Existence—Geographical Distribution and Dispersal of Organisms —The Descent of Man and later Works— Estimate of Darwin’s Life-Work .... 450*475

I

ON TIIE LAW WHICH IIAS REGULATED THE INTRODUCTION OP NEW SPECIES 1

Geographical Distribution dependent on Geologic Changes

Every naturalist who has directed Ms attention to the subject of the geographical distribution of animals and plants must have been interested in the singular facts which it presents. Many of these facts are quite different from what would have been anticipated, and have hitherto been considered as highly curious, but quite inexplicable. None of the explanations attempted from the time of Linnaeus are now considered at all satisfactory; none of them have given a cause sufficient to account for the facts known at the time, or comprehensive enough to include all the new facts which have since been, and are daily being, added. Of late years, however, a great light has been thrown upon the subject by geological investi¬ gations, which have shown that the present state of the earth and of the organisms now inhabiting it is hut the last stage of a long and uninterrupted series of changes which it has undergone, and consequently, that to endeavour to explain and account for its present condition without any reference to those changes (as has frequently been done) must load to very imperfect and erroneous conclusions.

The facts proved by geology are briefly these : That

1 Tliis article, written at Sarawak in February 1855 and publinked in the Annals and Magazine oj Matnral History, September 1855, was intended to show that some form of evolution of one species from another was needed in order to explain the various classes of facts hero indicated ; but at that time no means had been suggested by which the actual change of species could have been brought about.

NATUEAL SELECTION

I during an immense "but unknown period the surface of the earth has undergone successive changes; land has sunk be¬ neath the ocean, while fresh land has risen up from it; 1

mountain chains have been elevated; islands have been formed into continents, and continents submerged till they have become islands ; and these changes have taken place, not once merely, but perhaps hundreds, perhaps thousands of ;

times.— That all these operations have been more or less 1

continuous but unequal in their progress, and diming the whole series the organic life of the earth has undergone a corresponding alteration. This alteration also has been gradual, hut complete; after a certain interval not a single species existing which had lived at the commencement of the period. This complete renewal of the forms of life also ;

appears to have occurred several times.—That from the last of the geological epochs to the present or historical epoch, the change of organic life has been gradual: the first appear¬ ance of animals now existing can in many cases he traced, their numbers gradually increasing in the more recent forma¬ tions, while other species continually die out and disappear, ^

so that the present condition of the organic world is clearly I

derived by a natural process of gradual extinction and crea- ;

tion of species from that of the latest geological periods. j

We may therefore safely infer a like gradation and natural I

sequence from one geological epoch to another. ;

Now, taking this as a fair statement of the results of geological inquiry, we see that the present geographical dis¬ tribution of life upon the earth must be the result of all the

previous changes, both of the surface of the earth itself and

of its inhabitants. Many causes, no doubt, have operated of which we must ever remain in ignorance, and we may, there¬ fore, expect to find many details very difficult of explanation, and in attempting to give one, must allow ourselves to call into our service geological changes which it is highly probable may have occurred, though we have no direct evidence of their individual operation.

The great increase of our knowledge within the last twenty years, both of the present and past history of the organic world, has accumulated a body of facts which should afford a sufficient foundation for a comprehensive law embracing and

I

THE INTRODUCTION OP FEW SPECIES explaining them all, and giving a direction to new researches. It is about ten years since the idea of such a law suggested itself to the writer of this essay, and he has since taken every opportunity of testing it by all the newly-ascertained facts with which he has become acquainted, or has been able to observe himself. These have all served to convince him of the correctness of his hypothesis. Fully to enter into such a subject would occupy much space, and it is only in con¬ sequence of some views having been lately promulgated, he believes, in a wrong direction, that he now ventures to present his ideas to the public, with only such obvious illustrations of the arguments and results as occur to him in a place far removed from all means of reference and exact information.

A Law deduced from well-known Geographical md Geological Facts

The following propositions in Organic Geography and Geo¬ logy give the main facts on which the hypothesis is founded.

GEOGRAPHY

1. Large groups, such as classes and orders, are generally spread over the whole earth, while smaller ones, such as families and genera, are frequently confined to one portion, often to a very limited district.

2. In widely distributed families the genera are often limited in range; in widely distributed genera well-marked groups of species are peculiar to each geographical district.

3. When a group is confined to one district, and is rich in species, it is almost invariably the case that the most closely allied species are found in the same locality or in closely adjoining localities, and that therefore the natural sequence of the species by affinity is also geographical.

4. In countries of a similar climate, but separated by a wide sea or lofty mountains, the families, genera, and species of the one are often represented by closely allied families, genera, and species peculiar to the other.

GEOLOGY

5. The distribution of the organic world in time is very similar to its present distribution in space.

i

6. Most of the larger and some small-groups extend through several geological periods.

7. In each period, however, there are peculiar groups, found nowhere else, and extending through one or several formations.

8. Species of one genus, or genera of one family' occurring in the same geological time, are more closely allied than those separated in time.

9. A.s, generally, in geography no species or genus occurs in two very distant localities without being also found in intermediate places, so in geology the life of a species or genus .has not been interrupted. In other words, no group or species has come into existence twice.

10. The following law may he deduced from these facts : Every species has come into existence coincident both in space and time with a pre-existing closely allied species.

This law agrees with, explains, and illustrates all the facts connected with the following branches of the subject: 1st, The system of natural affinities. 2d, The distribution of animals and plants in space. 3d, The same in time, including all the phenomena of representative groups, and those which Professor Forbes supposed to manifest polarity. 4th, The phenomena of rudimentary organs. We will briefly endeavour to show its bearing upon each of these.

The Form of a, true system of Classification determined by this Law

If the law above enunciated be true, it follows that the natural series of affinities will also represent the order in which the several species came into existence, each one having had for its immediate antitype a closely allied species existing at the time of its origin. It is evidently possible that two or three distinct species may have had a common antitype, and that each of these may again have become the antitypes from which other closely allied species were created. The effect of this would he, that so long as each species has had but one new species formed on its model, the line of affinities will be simple, and may be represented by placing the several species in direct succession in a straight line. But if two or more species have been independently formed on the plan of a

I common antitype, then the series of affinities will he com¬ pound, and can only be represented by a forked or manybranched line. Now, all attempts at a Natural classification and arrangement of organic beings show that both these plans have obtained in creation. Sometimes the series of affinities can be well represented for' a space by a direct progression from species to species or from group to group, but it is generally found impossible so to continue. There constantly occur two or more modifications of an organ or modifications of two distinct organs, leading us on to two distinct series of species, which at length differ so much from each other as to form distinct genera or families. These are the parallel series or representative groups of naturalists, and they often occur in different countries, or are found fossil in different forma¬ tions. They are said to have an analogy to each other when they are so far removed from their common antitype as to differ in many important points of structure, while they still preserve a family resemblance. We thus see how difficult it is to determine in every case whether a given relation is an analogy or an affinity, for it is evident that as we go hack along the parallel or divergent scries, towards the common antitype, the analogy which existed between the two groups becomes an affinity. We are also made aware of the diffi¬ culty of arriving at a true classification, even in a small and perfect group; in the actual state of nature it is almost impossible, the species being so numerous and the modifica¬ tions of form and structure so varied, arising probably from the immense number of species which have served as anti¬ types for the existing species, and thus produced a compli¬ cated branching of the lines of affinity, as intricate as the twigs of a gnarled oak or the vascular system of the human body. Again, if we consider that we have only fragments of this vast system, the stem and main branches being repre¬ sented by extinct species of which, we have no knowledge, while a vast mass of limbs and boughs and minute twigs and scattered leaves is what we have to place in order, so as to determine the true position which each originally occupied with regard to the others, the whole difficulty of the true Natural System of classification becomes apparent to us.

We shall thus find ourselves obliged to reject all those

KATUR1L SELECTION i systems of classification which arrange species or groups in circles, as well as those which fix a definite number for the divisions of each group. The latter class have been very generally rejected by naturalists, as contrary to nature, notwithstanding the ability with which they have been advocated ; but the circular system of affinities seems to have obtained a deeper hold, many eminent naturalists having to some extent adopted it. Wv have, however, never been able to find a case in which the circle has been closed by a direct and close affinity. In most cases a palpable analogy has been substituted, in others the affinity is very obscure or altogether doubtful. The complicated branching of the lines of affinities in extensive groups must also afford great facilities for giving a show of probability to any such purely artificial arrange¬ ments. Their death-blow was given "by the admirable paper of the lamented Mr. Strickland, published in the Annals of Natural History , in which he so clearly showed the true synthetical method of discovering the Natural System.

Geographical Distribution of Organisms

If we now consider the geographical distribution of animals and plants upon the earth, we shall find all the facts beautifully in accordance with, and readily explained by, the present hypothesis. A country having species, genera, and whole families peculiar to it, will he the necessary result of its having been isolated for a long period, sufficient for many series of species to have been created on the type of pre¬ existing ones, which, as well as many of the earlier-formed species, have become extinct, and thus made the groups appear isolated. If in any ease the antitype had an extensive range, two or more groups of species might have been formed, each varying from it in a different manner, and thus producing several representative or analogous groups. The Sylviadoe of Europe and the Sylvicolidse of North America, the Heliconidse of South America and the Euploeas of the East, the group of TYogons inhabiting Asia and that peculiar to South America, are examples that may he accounted for in this manner.

Such phenomena as are exhibited by the Galapagos Islands, which contain little groups of plants and animals peculiar to themselves, but most nearly allied to those of South America,

I liave not hitherto received any, even a conjectural explana¬ tion. The Galapagos are a volcanic group of high antiquity, and have probably never been more closely connected with the continent than they are at present. They must have been first peopled, like other newly-formed islands, by the action of winds and currents, and at a period sufficiently remote to have had the original species die out, and the modi¬ fied prototypes only remain. In the same way we can account for the separate islands having each their peculiar species, either on the supposition that the same original emigration peopled the whole of the islands with the same species from which differently modified prototypes were created, or that the islands were successively peopled from each other, but that new species have been created in e'ach on the plan of the pre¬ existing ones. St. Helena is a similar case of a very ancient island having obtained an entirely peculiar, though limited, flora. On the other hand, no example is known of an island which can be proved geologically to be of very recent origin (late in the Tertiary, for instance), and yet possesses generic or family groups, or even many species peculiar to itself.

When a range of mountains has attained a great eleva¬ tion, and has so remained during a long geological period, the species of the two sides at and near their bases will be often very different, representative species of some genera occurring, and even whole genera being peculiar to one side only, as is remarkably seen in the case of the Andes and Eocky Mountains. A similar phenomenon occurs when an island has been separated from a continent at a very early period. The shallow sea between the Peninsula of Malacca, Java, Sumatra, and Borneo was probably a continent or large island at an early epoch, and may have become submerged as the volcanic ranges of Java and Sumatra were elevated ; the organic results we see in the very considerable number of species of animals common to some or all of these countries, while at the same time a number of closely allied repre¬ sentative species exist peculiar to each, showing that a con¬ siderable period has elapsed since their separation. The facts of geographical distribution and of geology may thus mutu¬ ally explain each other in doubtful cases, should the prin¬ ciples here advocated be clearly established.

i

In all those cases in which an island has been separated from a continent, or raised by volcanic or coralline action from the sea, or in which a monntain-chain has been elevated in a recent geological epoch, the phenomena of peculiar groups or even of single representative species will not exist. Our own island is an example of this, its separation from the continent being geologically very recent, and we have con¬ sequently scarcely a species which is peculiar to it; while the Alpine range, one of the most recent mountain elevations, separates faunas and floras which scarcely differ more than may he due to climate and latitude alone.

The series of facts alluded to in Proposition (3), of closely allied species in rich groups being found geographically near each other, is most striking and important. Mr. Lovell Reeve has well exemplified it in his able and interesting paper on the Distribution of the Bulimi. It is also seen in the Humming-birds and Toucans, little groups of two or three closely allied species being often found in the same or closely adjoining districts, as we have had the good fortune of per¬ sonally verifying. Pishes give evidence of a similar kind : each great river has its peculiar genera, and in more extensive genera its groups of closely allied species. But it is the same throughout Nature ; every class and order of animals will contribute similar facts. Hitherto no attempt has been made to explain these singular phenomena, or to show how they have arisen. Why are the genera of Palms and of Orchids in almost every case confined to one hemisphere 1 Why are the closely allied species of brown-backed Trogons all found in the East, and the green-backed in the West 1 Why are the Macaws and the Cockatoos similarly restricted 1 Insects furnish a countless number of analogous examples— the G-oliathi of Africa, the Ornithopterae of the Indian Islands, the Heliconidae of South America, the Danaidae of the East, and in all the most closely allied species found in geographical proximity. The question forces itself upon every thinking mind. Why are these things so ? They could not be as they are had no law regulated their creation and dispersion. The law here enunciated not merely ex¬ plains but necessitates the facts we see to exist, while the vast and long - continued geological changes of the earth

I

II readily account for the exceptions and apparent discrepancies that here and there occur. The writer’s object in putting forward his views in the present imperfect manner is to submit them to the test of other minds, and to be made aware of all the facts supposed to be inconsistent with them. As his hypothesis is one which claims acceptance solely as explaining and connecting facts which exist in nature, he expects facts alone to be brought to disprove it, not h priori arguments against its probability.