This principle of variation was no doubt much more active back in geologic time, during the early history of animal life upon the globe, than it is in this late age. And for the reason that animal life was less adapted to its environment than it is now, the struggle for life was sharper. Perfect adaptation of any form of life to the conditions surrounding it seems to check variability. Animal and plant life seem to vary more in this country than in England because the conditions of life are harder. The extremes of heat and cold, of wet and dry, are much greater. It has been found that the eggs of the English sparrow vary in form and color more in the United States than in Great Britain. Certain American shells are said to be more variable than the English. Among our own birds it has been found that the "migratory species evince a greater amount of individual variation than do non-migrating species" because they are subject to more varying conditions of food and climate. I think we may say, then, if there were no struggle for life, if uniformity of temperature and means of subsistence everywhere prevailed, there would be little or no variation and no new species would arise. The causes of variation seem to be the inequality and imperfection of things; the pressure of life is unequally distributed, and this is one of Nature's ways that accounts for much that we see about us.
VIII
WHAT DO ANIMALS KNOW?
After the discussion carried on in the foregoing chapters touching the general subject of animal life and instinct, we are prepared, I think, to ask with more confidence, What do animals know?
The animals unite such ignorance with such apparent knowledge, such stupidity with such cleverness, that in our estimate of them we are likely to rate their wit either too high or too low. With them, knowledge does not fade into ignorance, as it does in man; the contrast is like that between night and day, with no twilight between. So keen one moment, so blind the next!
Think of the ignorance of the horse after all his long association with man; of the trifling things along the street at which he will take fright, till he rushes off in a wild panic of fear, endangering his own neck and the neck of his driver. One would think that if he had a particle of sense he would know that an old hat or a bit of paper was harmless. But fear is deeply implanted in his nature; it has saved the lives of his ancestors countless times, and it is still one of his ruling passions.
I have known a cow to put her head between two trees in the woods—a kind of natural stanchion—and not have wit enough to get it out again, though she could have done so at once by lifting her head to a horizontal position. But the best instance I know of the grotesque ignorance of a cow is given by Hamerton in his "Chapters on Animals." The cow would not "give down" her milk unless she had her calf before her. But her calf had died, so the herdsman took the skin of the calf, stuffed it with hay, and stood it up before the inconsolable mother. Instantly she proceeded to lick it and to yield her milk. One day, in licking it, she ripped open the seams, and out rolled the hay. This the mother at once proceeded to eat, without any look of surprise or alarm. She liked hay herself, her acquaintance with it was of long standing, and what more natural to her than that her calf should turn out to be made of hay! Yet this very cow that did not know her calf from a bale of hay would have defended her young against the attack of a bear or a wolf in the most skillful and heroic manner; and the horse that was nearly frightened out of its skin by a white stone, or by the flutter of a piece of newspaper by the roadside, would find its way back home over a long stretch of country, or find its way to water in the desert, with a certainty you or I could not approach.
The hen-hawk that the farm-boy finds so difficult to approach with his gun will yet alight upon his steel trap fastened to the top of a pole in the fields. The rabbit that can be so easily caught in a snare or in a box-trap will yet conceal its nest and young in the most ingenious manner. Where instinct or inherited knowledge can come into play, the animals are very wise, but new conditions, new problems, bring out their ignorance.