in the destruction of those in which it is imperfectly or abnormally developed, and the preservation of those individuals which exhibit any advantageous variation.
In order to place the phenomena of instinct upon the same footing, with reference to natural selection, as is held by other manifestations of life, it is only necessary to show that instincts vary, and that these variations may become hereditary.
Not a great many years ago the statement that instinct varies among animals of the same species would have been met by a flat denial, but no one at all acquainted with the subject would probably now be found to dispute it. A few examples may not be out of place, however.
The oriole now builds its hanging-nest with the pieces of string, horse-hair, yarn, and carpet-ravelings, which are to be found in abundance about houses and barns; and I have seen a nest into which three fish-lines, with their hooks and sinkers, several yards of kite-tail from a telegraph wire, and a shoe-string, were interwoven. Of course, it is not natural for the bird to use such material as this, but the odds and ends furnished by man are much better fitted to its needs than the grass and fibres used by its less civilized ancestors. This change certainly shows power to improve in accordance with changed conditions; but it may perhaps be said that it is not an example of change in an instinct, but simply in a non-hereditary habit. The fear of man, shown by almost all the smaller animals, is in many cases newly acquired, for in regions uninhabited by man it is not shown, and it is only as the animals of such regions learn, by generations of persecution, that man is highly and peculiarly dangerous, that they come to avoid him; yet this fear is truly instinctive, for it is shown by the young as well as by the adult. The testimony of travelers as to the tameness of animals in regions where they have never been persecuted, is well known. For instance, Darwin, in his "Journal" of the voyage of the Beagle, says: "This disposition is common to all the terrestrial species of the Galapagos Islands, namely, to the mocking-thrush, the finches, wrens, tyrant fly-catchers, the dove, and carrion-buzzard.All of them often approached sufficiently near to be killed with a switch, and sometimes, as I myself tried, with a cap or hat. A gun here is almost superfluous, for with the muzzle I pushed a hawk off the branch of a tree. One day, while lying down, a mocking-thrush alighted on the edge of a pitcher made of the shell of a tortoise, which I held in my hand, and began very quietly to sip the water; it allowed me to lift it from the ground, while seated on the vessel. I often tried and very nearly succeeded in catching these birds by their legs. Formerly these birds appear to have been even tamer than at present. Cowley (in the year 1684) says that 'the turtledoves were so tame that they would often alight upon our hats and arms, so that we could take them alive, they not fearing man until
