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 conception. Several
reasons make me believe in this; but the chief one is the remarkable
effect which confinement or cultivation has on the functions of the
reproductive 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. Nothing 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 confinement 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! In
some few such cases it has been found out 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 this
curious subject; but to show how singular the laws are which determine
the reproduction of animals under confinement, I may just mention that
carnivorous animals, even from the tropics, breed in this country
pretty freely under confinement, with the exception of the
plantigrades or bear family; whereas, carnivorous birds, with the
rarest exceptions, hardly ever lay fertile eggs.
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