Page:Popular Science Monthly Volume 52.djvu/806

784 we had taken our last drive, my companion gave our driver a small fee, saying that it was because he was such a good botanist, for he really had been able to tell us the popular names of many plants. He laughed, and as he seemed so much pleased, I said, "James, I suppose you know what botanist means?" "Yes," he answered, "I 'spose it's some kind of a good boy."



T is easy to understand how natural selection may modify organisms for the good of the species, even at the expense of the individuals which, in each generation, make up the species; but it is difficult to understand how this can be brought about by nurture, for, so far as the direct action of the conditions of life is concerned, the species is identical with the sum of the individuals which now exist. No illustration of the law that the adaptations of living Nature are for the good of the species, and that when this comes into conflict with the welfare of the individuals, these are sacrificed, is more simple or more easy to understand than that afforded by some of the phenomena of migration.

The young salmon which is born in a mountain stream is soon impelled, by something in its nature, to journey downward, even for many hundred miles, until it reaches the unknown ocean, where it would discover, if it had faculties for anything so subjective as discovery, that, while it was born in a little brook, it was made for life in the great ocean. It has brought from its mountain home a natural aptitude for eluding all the strange enemies and for avoiding all the novel dangers which it meets in this new world, and it leads an active, predatory life, fiercely pursuing and destroying its natural but hitherto unknown prey; for growing rapidly, and quickly acquiring all the characteristics of the adult salmon, and storing up the intense nervous energy and the muscular strength which will be needed for forcing its way up the rapids in the mountain torrents, for leaping waterfalls, and fighting for its passage, where it long ago darted down with the current. As sexual maturity approaches, some stimulus, which has its origin in the developing reproductive organs, impels it to leave the ocean and, entering the mouth of a river, to journey upward, often a thousand miles or more, to its sources in the mountains.

At this time the king of fishes, as it is well called, is in physical perfection, with few rivals in beauty or strength or fierce energy, or