WHAT IS EVOLUTION?
(FROM THE ATLANTIC MONTHLY, MARCH, ’93.)
BY PROFESSOR E.S. HOLDEN.
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 again.
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 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.