-- 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 --
![](qr/10510/9.png)
Continue reading on your phone by scaning this QR Code
Tip: The current page has been bookmarked automatically. If you wish to continue reading later, just open the
Dertz Homepage, and click on the 'continue reading' link at the bottom of the page.