Chap. I. VARIATION UNDER DOMESTICATION. 
7 
CHAPTEE 1. 
Vaeiation undee Domestication. 
Causes of Variability—Effects of Habit—Correlation of Growth— 
Inheritance — Character of Domestic Varieties — Difficulty of 
distinguishing between Varieties and Species—Origin of Domestic 
Varieties from one or more Species — Domestic Pigeons, their 
Differences and Origin—Principle of Selection anciently followed, 
its Effects — Methodical and Unconscious Selection — Unknown 
Origin of our Domestic Productions—Circumstances favourable 
to Man's power of Selection. 
When we look to the individuals of the same variety 
or sub-variety of our older cultivated plants and ani¬ 
mals, one of the first points which strikes us, is, that 
they generally differ more from each other than do the 
individuals of any one species or variety in a state of 
nature. When we refiect on the vast diversity of the 
plants and animals which have been cultivated, and 
which have varied during all ages under the most 
difierent climates and treatment, I think we are driven 
to conclude that this great variability is simply due to 
our domestic productions having been raised under con¬ 
ditions of life not so uniform as, and somewhat different 
from, those to which the parent-species have been exposed 
under nature. There is also, I think, some probability 
in the view propounded by Andrew Knight, that this 
variability may be partly connected with excess of food. 
It seems pretty clear that organic beings must be ex¬ 
posed during several generations to the new conditions 
of life to cause any appreciable amount of variation; 
and that when the organisation has once begun to vary, 
it generally continues to vary for many generations. 
