8 
VABIATIOK 
Chap. I. 
No case is on record of a variable being ceasing to be 
variable under cultivation. Our oldest cultivated plants, 
sucb as wheat, still often yield new varieties: our oldest 
domesticated animals are still capable of rapid improve¬ 
ment or modification. 
It has been disputed at what period of life the causes 
of variability, whatever they may be, generally act; 
whether during the early or late period of development 
of the embryo, or at the instant of conception. Geoffroy 
St. Hilaire’s experiments show that unnatural treatment 
of the embryo causes monstrosities; and monstrosities 
cannot be separated by any clear line of distinction 
from mere variations. But I am strongly inclined to 
suspect that the most frequent cause of variability may 
be attributed to the male and female reproductive 
elements having been affected prior to the act of con¬ 
ception. Several reasons make me believe in this; but 
the chief one is the remarkable effect which confine¬ 
ment or cultivation has on the function of the repro¬ 
ductive system; this system appearing to be far more 
susceptible than any other part of the organisation, to 
the action of any change in the conditions of life. No¬ 
thing is more easy than to tame an animal, and few 
things more difficult than to get it to breed freely under 
confinement, even in the many cases when the male and 
female unite. How many animals there are which will 
not breed, though living long under not very close con¬ 
finement in their native country! This is generally 
attributed to vitiated instincts; but how many cultivated 
plants display the utmost vigour, and yet rarely or never 
seed I In some few such cases it has been discovered 
that very trifling changes, such as a little more or less 
water at some particular period of growth, will determine 
whether or not the plant sets a seed. I cannot here 
enter on the copious details which I have collected on 
