therefore, may be said to have been trying an experiment on a gigantic
scale; and it is an experiment which nature during the long lapse of time
has incessantly tried. Hence it follows that the principles of
domestication are important for us. The main result is that organic beings
thus treated have varied largely, and the variations have been inherited.
This has apparently been one chief cause of the belief long held by some
few naturalists that species in a state of nature undergo change.

I shall in this volume treat, as fully as my materials permit, the whole
subject of variation under domestication. We may thus hope to obtain some
light, little though it be, on the causes of variability,--on the laws
which govern it, such as the direct action of climate and food, the effects
of use and disuse, and of correlation of growth,--and on the amount of
change to which domesticated organisms are liable. We shall learn something
of the laws of inheritance, of the effects of crossing different breeds,
and on that sterility which often supervenes when organic beings are
removed from their natural conditions of life, and likewise when they are
too closely interbred. During this investigation we shall see that the
principle of Selection is highly important. Although man does not cause
variability and cannot even prevent it, he can select, preserve, and
accumulate the variations given to him by the hand of nature almost in any
way which he chooses; and thus he can certainly produce a great result.
Selection may be followed either methodically and intentionally, or
unconsciously and unintentionally. Man may select and preserve each
successive variation, with the distinct intention of improving and altering
a breed, in accordance with a preconceived idea; and by thus adding up
variations, often so slight as to be imperceptible by an uneducated eye, he
has effected wonderful changes and improvements. It can, also, be clearly
shown that man, without any intention or thought of improving the breed, by
preserving in each successive generation the individuals which he prizes