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Show 86 NATURAL SELECTION. [CHAP. IV. the fleetest prey, a deer for instance, had from any change in the country increased in numbers, or that other prey had decreased in numbers, during that season of the year when the wolf is hardest pressed for food. I can un~er such circumstances see no reason to doubt that the swiftest and slimmest wolves would have the ·best chance of surviving, and so be preserved or selected,-provided always that they retained strength to master their prey at this or at some other period of the year, when they might be compelled to prey on other animals. I can see no more reason to doubt this, than that man can improve the fleetness of his greyhounds by careful and methodical selection or by that unconscious selection which results from each man trying to keep the best dogs without any thought of modifying the breed. Even without any change in the proportional nun1 bers of the animals on which our wolf preyed, a cub might be born with an innate tendency to pursue certain kinds of prey. Nor can this be thought very improbable; for we often observe great differences in the natural tendencies of our domestic animals ; one cat, for instance, taking to catch rats, another mice; one cat, according to Mr. St. John, bringing home 'Yinged gaine, another hares or rabbits, and another hunhng on marshy ground and almost nightly catching woodcocks or snipes. The tendency to catch rats rather than mice is known to be inherited. Now, if any slight innate change of habit or of structure benefited an individual wolf, it would have the best chance of surviving and of l~avin~ offspring. So~e of its young would probably Inhent the same habits or structure, and by the repeti~ion of this. process, a new variety might be formed whwh wo~ld mther supp~ant or coexist wHh the parent form of wolf. Or, again, the wolves inhabiting a mountainous district, and those frequenting the lowlands, would natur~lly be forced t~ hunt different prey; and from the continue~ preservati~n .of the individuals best fitted for the two sites, two varieties might slowly be formed. These varieties would cross and blend where they met; but to this subject of intercrossing we shall soon have to return. I may add, that, . . CHAP. IV.] NATURAL SELECTION. 87 according to Mr. Pierce, there are two varieties of the wolf inhabiting the Catskill Mountains in the United States, one ·with a light greyhound-like for1n, which pursue~ deer, and the other more bulky, with shorter legs, whiCh more frequently attacks the shepherd's flocks. · Let us now t~k~ a more complex case. Certain plants excrete a sweet JUICe, apparently for the sake of eliminating something injurious from their sap: this is effected by glands at the base of the stipules in so1ne LeO'uminosre ~n~ at the beak of the leaf of the common la~·el. Thi~ JUICe, though small in quantity, is greedily sought by Insects. Let us now suppose a little sweet juice or nectar to be excreted by the inner bases of the petals of a flower. In this case, insects in seeking the nectar would get dusted with pollen, and would certainly often transport the pollen fr01n one flower .to. the .sti~~a of another flower. The flowers of two distinct Indlviduals of the san1e species would thus get crossed; and the act of crossing we have good reason to believe (as will hereafter be ~ore fully alluded to), would produce very vigorous seedlings, which conseque?tJy would have the best chance of flourishing ~nd s?-rviving. Some of ~hese seedlings would probably Inherit th~ nectar-excreting power. Those individual flo'Yers whiCh had the largest glands or nectaries, and :WhiCh excreted most nectar, would be oftenest visited by Insects, and wo?-ld be oftenest crossed ; and so in the long run would gain the upper hand. Those flowers also which ~ad their s~amens and pistils placed, in r~latio~ ~o the Size and habits of the particular insects which visIted t~em, so as to favour in any degree the transportal of thmr pollen from flower to flower would likewise be favoured. o.r .selected. We Inight hav~ taken the case of ~nsects VISiting flowers for the sake of collecting pollen Instead of nectar ; and as pollen is formed for the sole object of fertilisatio~, its ~estruction appears a simple loss to th~ plant; yet If a httle pollen were carried, at first ?ccas1onally and then habitually, by the pollen-devouring 1nseets from flower to flower, and a cross thus effected al~hough nine-tent!Is of the pollen were destroyed, it might still be a great gain to the plant ; and those individuals |