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various for all of them to be detected. In this instance, climate has undoubtedly much to do with the changes observed; yet many other influences must co-operate with it. But, of all the perplexing problems that are presented to the student of variations in animals and plants, there are none more perplexing than the exceptional or monstrous births, and the "sports," that so frequently occur. Several examples of this kind have already been given in Chap. II., but something more may be said in this place in regard to such occurrences. It seems to be a general rule, that, the more a species has varied, the more it will vary; so that, when a gardener wishes to get a variation in a certain direction, he will do well to select plants that vary much from the usual form, even if they are changing in just the opposite direction to that desired, since they will be likely sooner or later to show variations in the direction that is wanted. But just why the variation begins is unknown; though it is a well-ascertained fact, that abundance of food has much to do with putting species into a condition to vary.
A striking instance of the fact that these extraordinary births, for some unknown reason,
1 Darwin, Animals and Plants, etc., ii. pp. 249, 250.
tend often to repeat themselves in a certain manner, is afforded by the case of the blackshouldered peacock. This kind differs greatly from the common peacock; being considerably smaller, and in both sexes differently colored from the latter. So decided are the points of contrast, that Mr. Sclater, a very high authority, insists that the black-shouldered bird is properly to be ranked as a distinct species. It has made its appearance, that is, been found originating from eggs of the common kind, not less than seven times in England, and has sometimes multiplied so fast, as after a little while to become the only kind in the flock of its owners. This happens, too, in spite of the fact that it is so much smaller and weaker than the latter as to be always beaten in the frequent fights of the males. Had the black-shouldered kind originated in the wild state, it would (as already explained in the passage quoted from Mr. Murphy) have been impossible to decide when or how it came into existence; and who would have hesitated to class it as a new species? Is it not likely that at least a part of the cases similar to that which Mr. Wallace reports, of a humming-bird found in only one spot, the
1 Darwin, Animals and Plants, etc., i. pp. 205-307.
crater of an extinct volcano in South America, may have for their explanation some such recent origin as that of the black-shouldered peacock?
Such apparent accidents as the birth of sixfingered and six-toed children, of others with scales all over the body, of albinos (individuals without the proper supply of coloring-matter in the eyes, skin, and hair), come under the head of sudden and unexplained changes, due, possibly, to some kind of pre-natal influence. Melanism, or the presence of too much coloring-matter, the exact opposite of albinism, is, like it, a condition occurring both among men and the lower animals. Most of these singular variations may at times become hereditary, as may also most of the “sports” in plants; so that it would be as possible to secure a race of six-fingered men as it was to stock farm after farm with the Ancon and the Mauchamp sheep. All are familiar with the wide propagation of albinos in the domesticated state, in the case of white mice and white rabbits.
In this connection it is important to notice the fact of correlated variation; that is, variation of several parts or organs together, whenever,
1 Island Life, p. 16.
from any cause, a change is produced in one of them.
It is not remarkable that the hair, fur, or wool of animals, their horns, and their teeth should vary together; for the zoologist has learned (from their material and their early mode of growth) to regard all of these structuires as intimately related to each other.
Accordingly we find in the often-quoted Mauchamp merinos, for example, the horns, like the wool, smooth and comparatively straight. Hairless dogs generally have imperfect teeth (sometimes only one on either side of the jaw). Not infrequently the male animal (as in the hog, some apes, and the horse) has more fully developed teeth, especially canine or eye teeth, and a more hairy body, or hair more fully developed on some part of the body, than is found in the females. And from similar correlation the curious hairy woman, Julia Pastrana, who had a full beard and a hairy forehead, had also two rows of teeth, one inside the other.1 White cats with blue eyes are generally deaf; but this; it may be, is only a special illustration of the general fact that albinos are usually endowed with less acute senses than most of their species. From the same cause, perhaps, in Virginia white pigs cannot be raised in certain localities, because they are poisoned by eating the paintroot. It has not been definitely ascertained whether this is due to the greater sensitiveness of the white pigs to the poisonous root, or to the fact that their sense of smell is not keen enough to enable them to detect it, while that of the black ones is keen enough for this. In the vegetable kingdom, the same sort of correlation exists, and to such an extent, that (to give one instance out of many) experienced growers of apples can even tell from the shape of the leaves of a new seedling, before it has ever borne fruit, pretty nearly what the character of the fruit will be. By this correlation of variations, a change set up in one part is likely to be accompanied by many other changes.
1 Darwin, Animals and Plants, etc., ii. p. 321.
In the foregoing portion of this chapter, only here and there an instance of specific change, out of the great store of accumulated evidence on the subject, has been cited; and, in reckoning up the amount of such change that has taken place during the entire life history of the earth, it must be remembered that the present, according to geologists, is an age of unusual
1 Origin of Species, p. 9. 2 Darwin, Animals and Plants, etc., ii. p. 324.