VI 
CONTENTS. 
CHAPTEE III. 
Struggle for Existence. 
Its bearing on natural selection—The term used in a wide sense— 
Geometrical powers of increase—Eapid increase of naturalised 
animals and plants—Nature of the checks to increase—Compe¬ 
tition universal — Effects of climate — Protection from the 
number of individuals—Complex relations of all animals and 
plants throughout nature—Struggle for life most severe between 
individuals and varieties of the same species ; often severe be- 
' tween species of the same genus—The relation of organism to 
organism the most important of all relations .. Page 60-79 
CHAPTEE IV. 
Natural Selection. 
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 inter¬ 
crosses between individuals of the same species — Circumstances 
favourable and unfavourable to Natural Selection, namely, 
intercrossing, isolation, number of individuals — Slow action — 
Extinction caused by Natural Selection — Divergence of Cha¬ 
racter, 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 .80-130 
CHAPTEE V. 
Laws of Variation. 
Effects of external conditions — Use and disuse, combined with 
natural selection; organs of flight and of vision — Acclimatisa¬ 
tion — Correlation of growth — 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 — Eeversions to 
long-lost characters — Summary.. .. 131-170 
