CHAPTER II ON THE VARIATION OF ORGANIC BEINGS IN A WILD STATE; ON THE NATURAL MEANS OF SELECTION; AND ON THE COMPARISON OF DOMESTIC RACES AND TRUE SPECIES. Variation Natural means of Selection Differences between “Races” and “Species”:—first, in their trueness or variability Difference between “Races” and “Species” in fertility when crossed Causes of Sterility in Hybrids Infertility from causes distinct from hybridisation Points of Resemblance between “Races” and “Species” External characters of Hybrids and Mongrels Summary Limits of Variation 81-111 CHAPTER III ON THE VARIATION OF INSTINCTS AND OTHER MENTAL ATTRIBUTES UNDER DOMESTICATION AND IN A STATE OF NATURE; ON THE DIFFICULTIES IN THIS SUBJECT; AND ON ANALOGOUS DIFFICULTIES WITH RESPECT TO CORPOREAL STRUCTURES. Variation of mental attributes under domestication Hereditary habits compared with instincts Variation in the mental attributes of wild animals Principles of Selection applicable to instincts Difficulties in the acquirement of complex instincts by Selection Difficulties in the acquirement by Selection of complex corporeal structures 112-132 {ix} PART II ON THE EVIDENCE FAVOURABLE AND OPPOSED TO THE VIEW THAT SPECIES ARE NATURALLY FORMED RACES, DESCENDED FROM COMMON STOCKS. CHAPTER IV ON THE NUMBER OF INTERMEDIATE FORMS REQUIRED ON THE THEORY OF COMMON DESCENT; AND ON THEIR ABSENCE IN A FOSSIL STATE 133-143 CHAPTER V GRADUAL APPEARANCE AND DISAPPEARANCE OF SPECIES. 144-150 Gradual appearance of species Extinction of species CHAPTER VI ON THE GEOGRAPHICAL DISTRIBUTION OF ORGANIC BEINGS IN PAST AND PRESENT TIMES. SECTION FIRST 151-174 Distribution of the inhabitants in the different continents Relation of range in genera and species Distribution of the inhabitants in the same continent Insular Faunas Alpine Floras Cause of the similarity in the floras of some distant mountains Whether the same species has been created more than once On the number of species, and of the classes to which they belong in different regions SECOND SECTION 174-182 Geographical distribution of extinct organisms Changes in geographical distribution Summary on the distribution of living and extinct organic beings SECTION THIRD 183-197 An attempt to explain the foregoing laws of geographical distribution, on the theory of allied species having a common descent Improbability of finding fossil forms intermediate between existing species CHAPTER VII ON THE NATURE OF THE AFFINITIES AND CLASSIFICATION OF ORGANIC BEINGS. 198-213 Gradual appearance and disappearance of groups What is the Natural System? On the kind of relation between distinct groups Classification of Races or Varieties Classification of Races and Species similar Origin of genera and families {x} CHAPTER VIII UNITY OF TYPE IN THE GREAT CLASSES; AND MORPHOLOGICAL STRUCTURES.