so many unfavourable chances, a few favoured individuals survive, becoming
more and more numerous from one generation to the next, in proportion as
the dangerous art of rearing the young is perfected. Slight variations in
one and the same direction form a definite whole; and at long last the
ancient precursor has become the Scolia of our own times.

By the aid of a vague phraseology which juggles with the secret of the
centuries and the unknown things of life, it is easy to build up a theory
in which our mental sloth delights, after being discouraged by difficult
researches whose final result is doubt rather than positive statement. But
if, so far from being satisfied with hazy generalities and adopting as
current coin the terms consecrated by fashion, we have the perseverance to
explore the truth as far as lies in our power, the aspect of things will
undergo a great change and we shall discover that they are far less simple
than our overprecipitate views declared them to be. Generalization is
certainly a most valuable instrument: science indeed exists only by virtue
of it. Let us none the less beware of generalizations which are not based
upon very firm and manifold foundations.

When these foundations are lacking, the child is the great generalizer. For
him, the feathered world consists merely of birds; the race of reptiles
merely of snakes, the only difference being that some are big and some are
little. Knowing nothing, he generalizes in the highest degree; he
simplifies, in his inability to perceive the complex. Later he will learn
that the Sparrow is not the Bullfinch, that the Linnet is not the
Greenfinch; he will particularize and to a greater degree each day, as his
faculty of observation becomes more fully trained. In the beginning he saw
nothing but resemblances; he now sees differences, but still not plainly
enough to avoid incongruous comparisons.