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 exposed 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.
No case is on record of a variable being ceasing to be variable under
cultivation. Our oldest cultivated plants, such as wheat, still often
yield new varieties: our oldest domesticated animals are still capable
of rapid improvement 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 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
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