A lover of trout-fishing has been writing lately upon the question as to whether the trout in much-fished rivers and lakes do or do not exhibit increased “wariness,” or even “intelligent caution” in avoiding the flies so cunningly thrown before or above them by the skilful angler. It is argued that there cannot really be any increased indisposition of trout to take the fly based on experience, because on an estimate of the number of trout in a river like the Test, and of the limited number of anglers, every fisherman would have to hook and lose some thousands of fish every year for the experience to be general among trout that the horrid artificial flies “hide a still more horrid hook.” It is, of course, held that the trout cannot communicate their experiences to one another by any form of conversation (though leadership and imitative habit might have some effect), and it is also not suggested that a trout which had acquired an overpowering aversion to the angler’s fly as a result of being hooked and breaking free, could transmit that aversion to its offspring by the mere fact of reproduction. Hence it is maintained that there is no such increasing “wariness” in English and Scotch trout. It is a curious thing that in discussing this matter the fundamental principle should have been overlooked by which Darwin and Wallace have long ago explained to the satisfaction of naturalists, the aversions and cautious proceedings of all kinds of animals, from the smallest insects up to birds, beasts, and fishes. The principle of natural selection and survival of the fittest accounts for the increased caution of trout in well-fished rivers in the simplest way. Assume (as is perfectly reasonable) that some trout are more shy than others “by nature,” that is to say, are born so, that some are born with a slightly more rapid response to the sight of food than others—as one sees often enough with a lot of the young of any animal—then the increased shyness or pretended “intelligence” of the trout after many years’ fishing follows as a necessity. The rash fish are caught and destroyed, the shy fish remain in the river, and—here is the important point, a well-ascertained fundamental law of heredity—propagate their like. They produce shy fish. Every year this selection goes on till you get a race of fish in the well-fished river which are so shy that they cease to rise at all! This unpleasant result is avoided by the proprietors of trout streams to a certain extent by introducing a race of trout which has not in consequence of over-fishing developed an innate shyness of character (such as the Loch Leven and some others) to mix and breed with the timid over-fished race.