Thomas 6-3-36 32349 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 appear as a single volume I have thought it advisable to omit two essays that on "The Malayan Papilionida" as being too technical for general readers, and that on "The Distribution of Animals as indicating Geographical Changes," which contains 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 are two new chapters "The Antiquity of Man in North America" and "The Debt of Science to Darwin." Many corrections and some important additions have been 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 I. and II. of the present volume. Additional facts by Leroy, Spalding, Lowne, and Dixon on the Dr. Abbott on Nesting of Baltimore Oriole PAGES 108-112 114 Professor Jeitteles and Mr. Henry Reeks on Alterations in Mode of Nest-Building TROPICAL NATURE. Note on Dr. Shufeldt's Investigations into the Affinities of 115 337 CONTENTS I. ON THE LAW WHICH HAS REGULATED THE INTRODUCTION OF 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 II. ON THE TENDENCY OF VARIETIES TO DEPART INDEFINITELY 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 III. MIMICRY, AND OTHER PROTECTIVE RESEMBLANCES AMONG Test of true and false Theories-Importance of the Principle of Utility 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-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 How Instinct may be best Studied-Definition of Instinct-Does Man possess Instincts ?-How Indians travel through unknown and track- V. THE PHILOSOPHY OF BIRDS' NESTS Instinct or Reason in the Construction of Birds' Nests-Do Men build by 98-117 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 Laws from which the Origin of Species may be deduced-Mr. Darwin's |