We have a stake in all the past life of the globe. It is no doubt a scientific fact that your existence and mine were involved in the first cell that appeared, that the first zoophyte furthered our fortunes, that the first worm gave us a lift. Great good luck came to us when the first pair of eyes were invented, probably by the trilobite back in Silurian times; when the first ear appeared, probably in Carboniferous times; when the first pair of lungs grew out of a fish's air-bladder, probably in Triassic times; when the first four-chambered heart was developed and double circulation established, probably with the first warm-blooded animal in Mesozoic times.
These humble forms started the brain, the nervous system, the circulation, sight, hearing, smell; they invented the liver, the kidneys, the lungs, the heart, the stomach, and led the way to every organ and power my body and mind have to-day. They were the pioneers, they were the dim remote forebears, they conserved and augmented the fund of life and passed it along.
All their struggles, their discipline, their battles, their failures, their successes, were for you and me. Man has had the experience of all the animals below him. He has suffered and struggled as a fish, he has groveled and devoured as a reptile, he has fought and triumphed as a quadruped, he has lived in trees as a monkey, he has inhabited caves with the wolf and the bear, he has roamed the forests and plains as a savage, he has survived without fire or clothes or weapons or tools, he has lived with the mastodon and all the saurian monsters, he has held his own against great odds, he has survived the long battles of the land and the sea, he weathered the ice-sheet that overrode both hemispheres, he has seen many forms become extinct. In the historic period he has survived plague and pestilence, and want and famine. What must he have survived in prehistoric times! What must he have had to contend with as a cave-dweller, as a tree-dweller, as a river-drift man! Before he had tools or weapons what must he have had to contend with!
Nature was full of sap and rioted in rude strength well up to Quaternary times, producing extravagant forms which apparently she had no use for, as she has discontinued them.
In all these things you and I had our part and lot; of this prodigal outpouring of life we have reaped the benefit; amid these bizarre forms and this carnival of lust and power, the manward impulse was nourished and forwarded. In Eocene times nearly half the mammals lived on other animals; it must have been an age of great slaughter. It favored the development of fleetness and cunning, in which we too have an interest. Our rude progenitor was surely there in some form, and escaped the slaughter. Then or later it is thought he took to the trees to escape his enemies, as the rats in Jamaica have taken to the trees to escape the mongoose. To his tree-climbing we probably owe our hand, with its opposing thumb.
In all his disguises he is still our ancestor. His story reads like a fairy book. Never did nimble fancy of childhood invent such transformations—only the transformations are so infinitely slow, and attended with such struggle and suffering. Strike out the element of time and we have before us a spectacle more novel and startling than any hocus-pocus or legerdemain that ever set the crowd agape.
In every form man has passed through, he left behind some old member or power and took on some new. He left his air-bladder and his gills and his fins with the fishes; he got his lungs from the dipnoans, the precursors of the amphibians, and from these last he got his four limbs; he left some part of his anatomy with the reptile, and took something in exchange, probably his flexible neck. Somewhere along his line he picked up the four-chambered heart, the warm blood, the placenta, the diaphragm, the plantigrade foot, the mammary glands—indeed, what has he not picked up on the long road of his many transformations? He left some of his superfluous forty-four teeth with his ancestral quadrumana of Eocene times, and kept thirty-two. He picked up his brain somewhere on the road, probably far back in Palaeozoic times, but how has he developed and enlarged it, till it is now the one supreme thing in the world! His fear, his cunning, his anger, his treachery, his hoggishness—all his animal passions—he brought with him from his animal ancestors; but his moral and spiritual nature, his altruism, his veneration, his religious emotions, his aesthetic perceptions—have come to him as a man, supplementing his lower nature, as it were, with another order of senses—a finer sight, a finer touch, wrought in him by the discipline of life, and the wonder of the world about him, beginning de novo in him only as the wing began de novo in the bird, or the color began de novo in the flower—struck out from preexisting potentialities. The father of the eye is the light, and the father of the ear is the vibration of the air, but the father of man's higher nature is a question of quite another sort. About the only thing in his physical make-up that man can call his own is his chin. None of the orders below him seem to have what can strictly be called a chin.
Man owes his five toes and five fingers to the early amphibians of the sub-carboniferous times. The first tangible evidence of these five toes upon the earth is, to me, very interesting. The earliest record of them that I have heard of is furnished by a slab of shale from Pennsylvania, upon which, while it was yet soft mud, our first five-toed ancestor had left the imprint of his four feet. He was evidently a small, short-legged gentleman with a stride of only about thirteen inches, and he carried a tail instead of a cane. He was probably taking a stroll upon the shores of that vast Mediterranean Sea that occupied all the interior of the continent when he crossed his mud flat. It was raining that morning—how many million years ago?—as we know from the imprint of the raindrops upon the mud. Probably the shower did not cause him to quicken his pace, as amphibians rather like the rain. Just what his immediate forbears were like, or what the forms were that connected him with the fishes, we shall probably never know. Doubtless the great book of the rocky strata somewhere holds the secret, if we are ever lucky enough to open it at the right place. How many other secrets, that evolutionists would like to know, those torn and crumpled leaves hold!
It is something to me to know that it rained that day when our amphibian ancestor ventured out. The weather was beginning to get organized also, and settling down to business. It had got beyond the state of perpetual mist and fog of the earlier ages, and the raindrops were playing their parts. Yet, from all the evidence we have, we infer that the climate was warm and very humid, like that of a greenhouse, and that vegetation, mostly giant ferns and rushes and lycopods, was very rank, but there was no grass, or moss, no deciduous trees, or flowers, or fruit, as we know these things.
A German anatomist says that we have the vestiges of one hundred and eighty organs which have stuck to us from our animal ancestors,—now useless, or often worse than useless, like the vermiform appendix. Eleven of these superannuated and obsolete organs we bring from the fishes, four from amphibians and reptiles. The external ear is a vestige—of no use any more. Our dread of snakes we no doubt inherited from our simian ancestors.