April 2022

CHAPTER XIV Classification, groups subordinate to groups – Natural system – Rules and difficulties in classification, explained on the theory of descent with modification – Classification of varieties – Descent always used in classification – Analogical or adaptive characters – Affinities, general, complex, and radiating – Extinction separates and defines groups – Morphology, between members […]

CHAPTER XIII Distribution of fresh-water productions – On the inhabitants of oceanic islands – Absence of batrachians and of terrestrial mammals – On the relation of the inhabitants of islands to those of the nearest mainland – On colonisation from the nearest source with subsequent modifica­tion – Summary of the last and present chapter. Fresh-water

CHAPTER XII 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 of the level of the land, and by occasional means – Dispersal during the Glacial period*

CHAPTER XI On the slow and successive appearance of new species – On their different rates of change – Species once lost do not reappear – Groups of species follow the same general rules in their appearance and dis­appearance as do single species – On extinction – On simultaneous changes in the forms of life

CHAPTER X On the absence of intermediate varieties at the present day – On the nature of extinct intermediate varieties; on their number – On the lapse of time, as inferred from the rate of denudation and of deposi­tion – On the lapse of time as estimated by years – On the poorness of our

CHAPTER IX Distinction between the sterility of first crosses and of hybrids – Sterility various in degree, not universal, affected by close interbreeding, removed by domestication – Laws governing the sterility of hybrids – Sterility not a special endowment, but incidental on other differ­ences, not accumulated by natural selection – Causes of the sterility of

CHAPTER VIII Instincts comparable with habits, but different in their origin – Instincts graduated – Aphides and ants – Instincts variable – Domestic in­stincts, their origin – Natural instincts of the cuckoo, molothrus, ostrich, and parasitic bees – Slave-making ants – Hive-bee, its cell-making instinct – Changes of instinct and structure not necessarily simultaneous –

CHAPTER VII Longevity – Modifications not necessarily simultaneous – Modifications apparently of no direct service – Progressive development – Charac­ters of small functional importance, the most constant – Supposed incompetence of natural selection to account for the incipient stages of useful structures – Causes which interfere with the acquisition through natural selection of useful structures

CHAPTER VI Difficulties of the theory of descent with modification – Absence or rarity of transitional varieties – Transitions in habits of life – Diversified habits in the same species – Species with habits widely different from those of their allies – Organs of extreme perfection – Modes of transi­tion – Cases of difficulty –

CHAPTER V Effects of changed conditions – Use and disuse, combined with natural selection; organs of flight and of vision – Acclimatisation – Corre­lated variation – Compensation and economy of growth – False corre­lations – Multiple, rudimentary, and lowly organised structures variable – Parts developed in an unusual manner are highly variable; specific characters more

CHAPTER IV Natural Selection – its power compared with man’s selection – its power on characters of trifling importance – its power at all ages and on both sexes – Sexual selection – On the generality of intercrosses between individuals of the same species – Circumstances favourable and unfavourable to the results of Natural Selection,

CHAPTER III Its bearing on natural selection – The term used in a wide sense – Geo­metrical ratio of increase – Rapid increase of naturalized animals and plants – Nature of the checks to increase – Competition universal – Effects of climate – Protection from the number of individuals – Complex relations of all animals

CHAPTER II Variability – Individual differences – Doubtful species – Wide ranging, much diffused, and common species, vary most – Species of the larger genera in each country vary more frequently than the species of the smaller genera – Many of the species of the larger genera resemble varieties in being very closely, but unequally,

CHAPTER I Causes of variability – Effects of habit and the use or disuse of parts – Correlated variation – Inheritance – Character of domestic varieties – Difficulty of distinguishing between varieties and species – Origin of domestic varieties from one or more species – Domestic pigeons, their differences and origin – Principles of selection,