This interesting series of living evolutionary fossils—links that are not missing—is completed for us in some ways by the frogs and toads, which recapitulate, as it were, in their own lifetime just such an ancestral developmental history. Each of them begins life as essentially a fish—that is to say, as a tadpole breathing oxygen dissolved in water, by means of gills, and possessed of no limbs for terrestrial locomotion; he ends it as essentially a full-grown land-reptile, breathing atmospheric air by means of lungs, having discarded his now needless fin-fringed tail, and possessed of jumping legs of great muscular power. And the metamorphosis he thus undergoes answers exactly to just such a drying-up of the ponds that bore him. In early spring, when the temporary puddles are full of water, the parent frogs lay their spawn by hundreds in the ancestral element; and soon the little black tadpoles—true fish of a primitive type in all but name—swarm forth and swim in seething masses in the momentary medium. But as the sun begins to dry up the water in their dwelling-place they lose their fins and gills, pass from fish to amphibians, and shortly hop ashore, provided with four legs and a pair of lungs specially adapted for direct air-breathing. There we have a marvellous piece of evolutionary magic still going on every day before our eyes, which would sound incredible to us if a man of science reported it for the first time from Central Africa or New Guinea. The frog, in short, shows us successively in his own person the self-same stages of development which the various mud-fish preserve for us in distant regions, as types of distinct and unrelated species.
XXX.
AN INTERVIEW WITH A COCK-SPARROW.
“Believe me,” said the sparrow, “it pays to be civilized.”
“You seem to have found it so,” I answered. “You and the rook, I take it, are just the two of our birds which have lost nothing and gained much by man’s presence in our island.”
“I believe you,” said the sparrow, cocking his head on one side. He seemed ill to recognize the solemnity of being interviewed, which to the human subject is like having your photograph taken, combined with a compound visit to the dentist. “We are a dominant race, you see; that’s just where it is. We have adapted ourselves to the environment. Birds like jays and hawfinches, now, are too shy and retiring: as civilization advances, they retreat and skulk and can’t march with the age; but we and the rooks, we take advantage of every increase of human population to redouble our numbers. As fast as cultivation grows, we grow; man exists to provide us with food and shelter.”
“Then you think your race has increased, and is still increasing?” I asked.
“Not a doubt of it, my dear sir. We have multiplied enormously. Before the age of tillage, we were probably a small and unimportant group, no more conspicuous or remarkable in any way than the wretched little siskins, or the grasshopper-warblers. But as cultivation develops, we develop, if you will excuse my Latin, pari passu. (Oh, yes, I know Latin well, because a near cousin of mine is the Passer Italiæ.) However, as I was going to say when you interrupted me with a question, we have spread about everywhere that grain will grow in Europe. That’s because we are bold, courageous birds, not afraid of every passing object we see, like the bluethroats and the creepers; while at the same time we are cautious, quick, eager, and wary, and get out of the way of danger at a moment’s notice. My own opinion is that even in Europe we must have been a mere handful of birds before cultivation spread, and that since that time we have pushed ourselves by our energy and enterprise into a leading position. About great cities alone, we may be reckoned by our myriads; and then, just look at our colonial expansion!”
“You have emigrated largely, I believe,” I said, “to America and the Colonies?”
“Bless my soul, yes; we have followed European civilization almost everywhere. We allow mankind to go ahead of us for a few years, just to prepare the way, and get our corn and oats into working order; and then we gain a foothold in the newly acquired lands, and naturally oust the uncivilized natives. We have annexed America, and are killing out inferior types in many other regions. What do I mean by inferior types? Why, non-sparrows, of course; such lower grades, don’t you know, as Australians and New Zealanders.”
“Excuse my asking a delicate question, but do you do much damage, from the farmer’s point of view, to the crops and the gardens? You see, we men have a narrow-minded way of regarding these things from a somewhat restricted human standpoint.”