Contributions to the Theory of Natural Selection

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Alfred Russel Wallace. Contributions to the Theory of Natural Selection

PREFACE

PREFACE TO THE SECOND EDITION

I. ON THE LAW WHICH HAS REGULATED THE INTRODUCTION OF NEW SPECIES.1

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 Organization of very ancient Animals consistent with this Law

Objections to Forbes’ Theory of Polarity

Rudimentary Organs

Conclusion

II. ON THE TENDENCY OF VARIETIES TO DEPART INDEFINITELY FROM THE ORIGINAL TYPE.4

Instability of Varieties supposed to prove the permanent 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 Domesticated Varieties explained

Lamarck’s Hypothesis very different from that now advanced

Conclusion

III. MIMICRY, AND OTHER PROTECTIVE RESEMBLANCES AMONG ANIMALS

Importance of the Principle of Utility

Popular Theories of Colour in Animals

Importance of Concealment as Influencing Colour

Special Modifications of Colour

Theory of Protective Colouring

Objection that Colour, as being dangerous, should not exist in Nature

Mimicry

Mimicry among 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

Objections to Mr. Bates’ 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

IV. THE MALAYAN PAPILIONIDÆ OR SWALLOW-TAILED BUTTERFLIES, AS ILLUSTRATIVE OF THE THEORY OF NATURAL SELECTION

Special Value of the Diurnal Lepidoptera for enquiries of this nature

Question of the rank of the Papilionidæ

Distribution of the Papilionidæ

Definition of the word Species

Laws and Modes of Variation

Variation as specially influenced by Locality

Remarks on the facts of Local variation

Mimicry

Concluding remarks on Variation in Lepidoptera

Arrangement and Geographical Distribution of the Malayan Papilionidæ

Range of the Groups of Malayan Papilionidæ

Remarkable Peculiarities of the Island of Celebes

Concluding Remarks

V. 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 trackless Forests

VI. 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

Man’s Works mainly Imitative

Birds do Alter and Improve their Nests when altered Conditions require it

Conclusion

VII. 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 Explanation

Real or apparent Exceptions to the Law stated at page 240

Various modes of Protection of Animals

Females of some Groups require and obtain more Protection than the Males

Conclusion

VIII. CREATION BY LAW

Mr. Darwin’s Metaphors liable to Misconception

A Case of Orchis-structure explained by Natural Selection

Adaptation brought about by General Laws

Beauty in Nature

How new Forms are produced by Variation and Selection

The Objection that there are Limits to Variation

Objection to the Argument from Classification

The “Times,” on Natural Selection

Intermediate or generalized Forms of extinct Animals, an indication of Transmutation or Development

Conclusion

A Demonstration of the Origin of Species by Natural Selection

IX. THE DEVELOPMENT OF HUMAN RACES UNDER THE LAW OF 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 development 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

Conclusion

X. THE LIMITS OF NATURAL SELECTION AS APPLIED TO MAN

What Natural Selection can Not do

The Brain of the Savage shown to be Larger than he Needs it to be

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 produced by Natural Selection

Feet and Hands of Man, considered as Difficulties on the Theory of Natural Selection

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

Conclusion

NOTES

NOTE A. (Page360.)

NOTE B. (Page365.)

INDEX

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The flattering reception of my Essays by the public and the press having led to a second edition being called for within a year of its first publication, I have taken the opportunity to make a few necessary corrections. I have also added a few passages to the 6th and 7th Essays, and have given two notes, explanatory of some portions of the last chapter which appear to have been not always understood. These additions are as follows:—

The facts proved by geology are briefly these:—That during an immense, but unknown period, the surface of the earth has undergone successive changes; land has sunk beneath the ocean, while fresh land has risen up from it; 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 continuous, but unequal in their progress, and during the whole series the organic life of the earth has undergone a corresponding alteration. This alteration also has been gradual, but 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 appearance of animals now existing can in many cases be traced, their numbers gradually increasing in the more recent formations, while other species continually die out and disappear, so that the present condition of the organic world is clearly derived by a natural process of gradual extinction and creation of species from that of the latest geological periods. We may therefore safely infer a like gradation and natural sequence from one geological epoch to another.

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Another important series of facts, quite in accordance with, and even necessary deductions from, the law now developed, are those of rudimentary organs. That these really do exist, and in most cases have no special function in the animal oeconomy, is admitted by the first authorities in comparative anatomy. The minute limbs hidden beneath the skin in many of the snake-like lizards, the anal hooks of the boa constrictor, the complete series of jointed finger-bones in the paddle of the Manatus and whale, are a few of the most familiar instances. In botany a similar class of facts has been long recognised. Abortive stamens, rudimentary floral envelopes and undeveloped carpels, are of the most frequent occurrence. To every thoughtful naturalist the question must arise, What are these for? What have they to do with the great laws of creation? Do they not teach us something of the system of Nature? If each species has been created independently, and without any necessary relations with pre-existing species, what do these rudiments, these apparent imperfections mean? There must be a cause for them; they must be the necessary results of some great natural law. Now, if, as it has been endeavoured to be shown, the great law which has regulated the peopling of the earth with animal and vegetable life is, that every change shall be gradual; that no new creature shall be formed widely differing from anything before existing; that in this, as in everything else in Nature, there shall be gradation and harmony,—then these rudimentary organs are necessary, and are an essential part of the system of Nature. Ere the higher Vertebrata were formed, for instance, many steps were required, and many organs had to undergo modifications from the rudimental condition in which only they had as yet existed. We still see remaining an antitypal sketch of a wing adapted for flight in the scaly flapper of the penguin, and limbs first concealed beneath the skin, and then weakly protruding from it, were the necessary gradations before others should be formed fully adapted for locomotion.3 Many more of these modifications should we behold, and more complete series of them, had we a view of all the forms which have ceased to live. The great gaps that exist between fishes, reptiles, birds, and mammals would then, no doubt, be softened down by intermediate groups, and the whole organic world would be seen to be an unbroken and harmonious system.

It has now been shown, though most briefly and imperfectly, how the law that “Every species has come into existence coincident both in time and space with a pre-existing closely allied species,” connects together and renders intelligible a vast number of independent and hitherto unexplained facts. The natural system of arrangement of organic beings, their geographical distribution, their geological sequence, the phænomena of representative and substituted groups in all their modifications, and the most singular peculiarities of anatomical structure, are all explained and illustrated by it, in perfect accordance with the vast mass of facts which the researches of modern naturalists have brought together, and, it is believed, not materially opposed to any of them. It also claims a superiority over previous hypotheses, on the ground that it not merely explains, but necessitates what exists. Granted the law, and many of the most important facts in Nature could not have been otherwise, but are almost as necessary deductions from it, as are the elliptic orbits of the planets from the law of gravitation.

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