THE FOUNDATIONS OF THE ORIGIN OF SPECIES TWO ESSAYS WRITTEN IN 1842 AND 1844

CHAPTER I 57-80

ON THE VARIATION OF ORGANIC BEINGS UNDER DOMESTICATION;
AND ON THE PRINCIPLES OF SELECTION.

Variation
On the hereditary tendency
Causes of Variation
On Selection
Crossing Breeds
Whether our domestic races have descended from one or more wild stocks
Limits to Variation in degree and kind
In what consists Domestication--Summary


CHAPTER II 81-111

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


CHAPTER III 112-132

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


PART II

ON THE EVIDENCE FAVOURABLE AND OPPOSED TO THE VIEW
THAT SPECIES ARE NATURALLY FORMED RACES, DESCENDED
FROM COMMON STOCKS.


CHAPTER IV 133-143

ON THE NUMBER OF INTERMEDIATE FORMS REQUIRED ON THE
THEORY OF COMMON DESCENT; AND ON THEIR ABSENCE
IN A FOSSIL STATE


CHAPTER V 144-150

GRADUAL APPEARANCE AND DISAPPEARANCE OF SPECIES.

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 198-213

ON THE NATURE OF THE AFFINITIES AND CLASSIFICATION
OF ORGANIC BEINGS.

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


CHAPTER VIII 214-230

UNITY OF TYPE IN THE GREAT CLASSES; AND
MORPHOLOGICAL STRUCTURES.

Unity of Type
Morphology
Embryology
Attempt to explain the facts of embryology
On the graduated complexity in each great class
Modification by selection of the forms of immature animals
Importance of embryology in classification
Order in time in which the great classes have first appeared


CHAPTER IX 231-238

ABORTIVE OR RUDIMENTARY ORGANS.

The abortive organs of Naturalists
The abortive organs of Physiologists
Abortion from gradual disuse