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Young Folks' Library: Wonders of Earth, Sea and Sky

What Is Evolution?
From The Atlantic Monthly, March, '93.)
I was once trying to tell a boy, a friend of mine, what the scientific men mean by the long
word Evolution, and to give him some idea of the plan of the world. I wanted an
illustration of something that had grown—evolved, developed—from small beginnings
up through more and more complicated forms, till it had reached some very complete
form. I could think of no better example than the railway by which we were sitting. The
trains were running over the very track where a wagon-road had lately been, and before
that a country cart-track, and before that a bridle-path, and before that again a mere trail
for cattle. So I took the road for an example, and tried to show my boy how it had grown
from little things by slow degrees according to laws; and if you like, I will try to tell it
Just as one can go further and further back, and always find a bird to be the parent of the
egg, and an egg to be the parent of that bird, so in the history of [pg 128] this road of ours; we
may go back and back into the past, always finding something earlier, which is the cause
of the something later. The earth, the planets, and the sun were all a fiery mist long ago.
And in that mist, and in what came before it, we may look for the origin of things as they
are. But we must begin somewhere. Let us begin with the landscape as we see it now,—
hills, valleys, streams, mountains, grass,—but with only a single tree.
We will not try to say how the tree came there. At least, we will not try just yet. When we
are through with the story you can say just as well as I can.
Suppose, then, a single oak-tree stood just on that hillside thousands and thousands of
years ago. Grass was growing everywhere, and flowers, too. The seeds came with the
winds. Year after year the oak-tree bore its acorns, hundreds and hundreds of them, and
they fell on the grass beneath and rolled down the smooth slopes, and sprouted as best
they could,—most of them uselessly so far as producing trees were concerned,—but each
one did its duty and furnished its green sprout, and died if it found no nourishment.
All the hundreds of acorns rolled down the slopes, Not one rolled up; and here was a
law,—the law of gravitation,—in full activity. There were scores of other laws active,
too; for evolution had gone a long way when we had an earth fit to be lived on, and hills
in their present shape, and a tree bearing acorns that would reproduce their kind. But ever
since the fiery mist this simple law of gravitation has been acting, binding the whole
universe together, making a relationship between each clod and every other clod, and [pg 129]
forcing every stone, every acorn, and every rain-drop to move down and not up.
Just as this law operates,—continuously, silently, inexorably,—so every other law makes
itself felt in its own sphere. Gravitation is simple. The law according to which an acorn
makes an oak—and not a pine-tree is complex. But the laws of Nature are all alike, and if
we understand the simple ones, we can at least partly comprehend the more complex.
They are nothing but fixed habits on a large scale.
So the acorns fell year by year and sprouted; and one out of a thousand found good soil,
and was not wasted, and made a tree. And so all around (below) the tree with which we