The Origin of Species

Aberrant – Forms or groups of animals or plants which deviate in important characters from their nearest allies, so as not to be easily included in the same group with them, are said to be aberrant.Aberration (in Optics) – In the refraction of light by a convex lens the rays passing through different parts of […]

I will here give a brief sketch of the progress of opinion on the Origin of Species. Until recently the great majority of naturalists believed that species were immutable productions, and had been separately created. This view has been ably maintained by many authors. Some few natural­ists, on the other hand, have believed that species

CHAPTER XV Recapitulation of the objections to the theory of Natural Selection – Recapitulation of the general and special circumstances in its favour – Causes of the general belief in the immutability of species – How far the theory of Natural Selection may be extended – Effects of its adoption on the study of Natural

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