o 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