The Origin of Species by means of Natural Selection (6th ed) | Page 9

-- Circumstances favourable
and unfavourable to the results of Natural Selection, namely,
intercrossing, isolation, number of individuals -- Slow action --
Extinction caused by Natural Selection -- Divergence of Character,
related to the diversity of inhabitants of any small area and to
naturalisation -- Action of Natural Selection, through Divergence of
Character and Extinction, on the descendants from a common parent --
Explains the Grouping of all organic beings -- Advance in organisation
-- Low forms preserved -- Convergence of character -- Indefinite
multiplication of species -- Summary.


CHAPTER V.
LAWS OF VARIATION.

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 variable than generic; secondary sexual characters
variable -- Species of the same genus vary in an analogous manner --
Reversions to long-lost characters -- Summary.


CHAPTER VI.
DIFFICULTIES OF THE THEORY.
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 -- Natura non facit saltum --
Organs of small importance -- Organs not in all cases absolutely perfect
-- The law of Unity of Type and of the Conditions of Existence
embraced by the theory of Natural Selection.


CHAPTER VII.
MISCELLANEOUS OBJECTIONS TO THE THEORY OF
NATURAL SELECTION.
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 --
Gradations of structure with changed functions -- Widely different
organs in members of the same class, developed from one and the same
source -- Reasons for disbelieving in great and abrupt modifications.


CHAPTER VIII.
INSTINCT.
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 --
Difficulties on the theory of the Natural Selection of instincts -- Neuter
or sterile insects -- Summary.


CHAPTER IX.
HYBRIDISM.
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 first crosses and of hybrids -- Parallelism between the
effects of changed conditions of life and of crossing -- Dimorphism and

Trimorphism -- Fertility of varieties when crossed and of their mongrel
offspring not universal -- Hybrids and mongrels compared
independently of their fertility -- Summary.


CHAPTER X.
ON THE IMPERFECTION OF THE GEOLOGICAL RECORD.
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 in years -- On the poorness of our
palaeontological collections -- On the intermittence of geological
formations -- On the denudation of granitic areas -- On the absence of
intermediate varieties in any one formation -- On the sudden
appearance of groups of species -- On their sudden appearance in the
lowest known fossiliferous strata -- Antiquity of the habitable earth.


CHAPTER XI.
ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS.
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 throughout the world -- On the affinities of
extinct species to each other and to living species -- On the state of
development of ancient forms -- On the succession of the same types
within the same areas -- Summary of preceding and present chapter.

CHAPTER XII.
GEOGRAPHICAL DISTRIBUTION.
Present distribution cannot be accounted for by differences in physical
conditions -- Importance of barriers -- Affinity of the productions of the
same continent --