Page - 29 - in The Origin of Species

VARIATION UNDER DOMESTICATION 29 producing moss-roses—we clearly see that the nature of the condition is of subordinate importance in comparison with the nature of the organism in determining each particular form of variation—perhaps of not more importance than the nature of the spark, by which a mass of combustible matter is ignited, has in determining the nature of the flames. EFFECTS OF HABIT AND OF THE USE OR DISUSE OF PARTS; CORRELATED VARIATION; INHERITANCE Changed habits produce an inherited efifect, as in the pe- riod of the flowering of plants when transported from one climate to another. With animals the increased use or dis- use of parts has had a more marked influence; thus I find in the domestic duck that the bones of the wing weigh less and the bones of the leg more, in proportion to the whole skele- ton, than do the same bones in the wild duck; and this change may be safely attributed to the domestic duck flying much less, and walking more, than its wild parents. The great and inherited development of the udders in cows and goats in countries where they are habitually milked, in com- parison with these organs in other countries, is probably another instance of the effects of use. Not one of our do- mestic animals can be named which has not in some country drooping ears ; and the view which has been suggested that the drooping is due to disuse of the muscles of the ear, from the animals being seldom much alarmed, seems probable. Many laws regulate variation, some few of which can be dimly seen, and will hereafter be briefly discussed. I will here only allude to what may be called correlated variation. Important changes in the embryo or larva will probably en- tail changes in the mature animal. In monstrosities, the correlations between quite distinct parts are very curious; and many instances are given in Isidore Geoffroy St. Hilaire's great work on this subject. Breeders believe that long limbs are almost always accompanied by an elongated head. Some instances of correlation are quite whimsical : thus cats which are entirely white and have blue eyes are generally deaf ; but it has been lately stated by Mr. Tait that this is confined to the males. Colour and constitutional pecu-