82 SEXUAL SELECTION. 
with its own kind. The inevitable result is the survival of 
the fittest, t.e., those which are best adapted to their environ- 
ment live and reproduce their kind, and the less fit die early. 
The net result is a selection of the superabundant offspring 
which, as it occurs throughout nature, has been termed 
Natural Selection. Darwin’s theory of evolution by Natural 
Selection therefore depends upon two main principles or 
natural phenomena : - 
1. Variation, or the structural differences between a parent and 
its offspring. 
2. The struggle for existence, due to production of offspring above 
the means of subsistence. 
The second principle acting upon the first #us¢ result in a 
selection of the variations. All variations which tend to 
higher efficiency are preserved and intensified through many 
generations till a fresh species is produced. 
Animals under domestication are not, as a rule, subjected 
to a struggle for existence, and hence there is no natural 
selection. Man has, however, persistently selected the 
variations which appealed to his fancy, and by this a7tziczal 
selection has been enabled to produce the numerous breeds 
of dogs, horses, cattle, pigeons, rabbits, &c. In this case 
the mental faculties of man perform the selective opera- 
tion which is automatically effected in nature by the fierce 
struggle for life. 
It is questionable if these artificially produced ‘‘ breeds” are really 
comparable to the natural ‘‘ species” for, if the breeds are left to them- 
selves, rapid intercrossing results, in a few generations, in the 
disappearance of the ‘‘ breed” characteristics and a reversion to the 
primitive ancestors from which they were originally derived. 
SEXUAL SELECTION.—In certain cases, especially among 
the higher animals, the female individuals exercise a selective 
faculty among the males. Contests of various kinds take 
place among the males, and the successful competitors 
alone pair with the females. This form of natural selection, 
termed sexual selection, probably accounts for the production 
of the secondary sexual characters referred to in Chapter V. 
(See page 44.) 
Let us apply the Darwinian theory of evolution to 
the case of oceanic islands referred to in Chapter VII. (p. 64). 
Suppose a number of winged insects have been blown by a 
