Part 10 (2/2)
He studies the parasitical habit of the cuckoo and hits on an explanation of it. He speculates why the partridges and deer in South America are so tame.
His ”Voyage of the Beagle” alone would insure him lasting fame. It is a cla.s.sic among scientific books of travel. Here is a traveler of a new kind: a natural-history voyager, a man bent on seeing and taking note of everything going on in nature about him, in the non-human, as well as in the human world. The minuteness of his observation and the significance of its subject-matter are a lesson to all observers.
Darwin's interests are so varied and genuine. One sees in this volume the seed-bed of much of his subsequent work. He was quite a young man (twenty-four) when he made this voyage; he was ill more than half the time; he was as yet only an observer and appreciator of Nature, quite free from any theories about her ways and methods. He says that this was by far the most important event of his life and determined his whole career. His theory of descent was already latent in his mind, as is evinced by an observation he made about the relations.h.i.+p in South America between the extinct and the living forms. ”This relations.h.i.+p,”
he said, ”will, I do not doubt, hereafter throw more light on the appearance of organic beings on our earth, and their disappearance from it, than any other cla.s.s of facts.”
He looked into the muddy waters of the sea off the coast of Chile, and found a curious new form of minute life--microscopic animals that exploded as they swam through the water. In South America he saw an intimate relations.h.i.+p between the extinct species of ant-eaters, armadillos, tapirs, peccaries, guanacos, opossums, and so on, and the living species of these animals; and he adds that the wonderful relations.h.i.+p in the same continent between the dead and the living would doubtless hereafter throw more light on the appearance of organic beings on our earth, and their disappearance from it, than any other cla.s.s of facts.
His observation of the evidences of the rise and fall of thousands of feet of the earth along the Cordilleras leads him to make this rather startling statement: ”Daily it is forced home on the mind of the geologist that nothing, not even the wind that blows, is so unstable as the level of the crust of the earth.”
There is now and then a twinkle of humor in Darwin's eyes, as when he says that in the high alt.i.tude of the Andes the inhabitants recommend onions for the ”puna,” or shortness of breath, but that he found nothing so good as fossil sh.e.l.ls.
Water boils at such a low temperature in the high Andes that potatoes will not cook if boiled all night. Darwin heard his guides discussing the cause. ”They had come to the simple conclusion that 'the cursed pot' (which was a new one) did not choose to boil potatoes.”
In all Darwin's record we see that the book of nature, which ordinary travelers barely glance at, he opened and carefully perused.
V
Natural Selection turns out to be of only secondary importance. It is not creative, but only confirmative. It is a weeding-out process; it is Nature's way of improving the stock. Its tendency is to make species more and more hardy and virile. The weak and insufficiently endowed among all forms tend to drop out. Life to all creatures is more or less a struggle, a struggle with the environment, with the inorganic forces,--storm, heat, cold, sterile land, and engulfing floods,--and it is a struggle with competing forms for food and shelter and a place in the sun. The strongest, the most amply endowed with what we call vitality or power to live, win. Species have come to be what they are through this process. Immunity from disease comes through this fight for life; and adaptability--through trial and struggle species adapt themselves, as do our own bodies, to new and severe conditions. The naturally weak fall by the wayside as in an army on a forced march.
Every creature becomes the stronger by the opposition it overcomes.
Natural Selection gives speed, where speed is the condition of safety, strength where strength is the condition, keenness and quickness of sense-perception where these are demanded. Natural Selection works upon these attributes and tends to perfect them. Any group of men or beasts or birds brought under any unusual strain from cold, hunger, labor, effort, will undergo a weeding-out process.
Populate the land with more animal life than it can support, or with more vegetable forms than it can sustain, and a weeding-out process will begin. A fuller measure of vitality, or a certain hardiness and toughness, will enable some species to hold on longer than others, and, maybe, keep up the fight till the struggle lessens and victory is won.
The flame of life is easily blown out in certain forms, and is very tenacious in others. How unequally the power to resist cold, for instance, seems to be distributed among plants and trees, and probably among animals! One spring an unseasonable cold snap in May (mercury 28) killed or withered about one per cent of the leaves on the lilacs, and one tenth of one per cent of the leaves of our crab-apple tree. In the woods around Slabsides I observed that nearly half the plants of Solomon's-seal (_Polygonatum_) and false Solomon's-seal (_Smilacina_) were withered. The vital power, the power to live, seems stronger in some plants than in others of the same kind. I suppose this law holds throughout animate nature. When a strain of any kind comes, these weaker ones drop out. In reading the stories of Arctic explorers, I see this process going on among their dog-teams: some have greater power of endurance than others. A few are constantly dropping out or falling by the wayside. With an army on a forced march the same thing happens. In the struggle for existence the weak go to the wall. Of course the struggle among animals is at least a toughening process. It seems as if the old Indian legend, that the strength of the foe overcome pa.s.ses into the victor, were true. But how a new species could arrive as the result of such struggle is past finding out.
Variation with all forms of life is more or less constant, but it is around a given mean. Only those acquired characters are transmitted that arise from the needs of the organism.
A vast number of changes in plants and animals are superficial and in no way vital. It is hard to find two leaves of the same tree that will exactly coincide in all their details; but a difference that was in some way a decided advantage would tend to be inherited and pa.s.sed along. It is said that the rabbits in Australia have developed a longer and stronger nail on the first toe of each front foot, which aids them in climbing over the wire fences. The aye-aye has a specially adapted finger for extracting insects from their hiding-places. Undoubtedly such things are inherited. The snowshoes of the partridge and rabbit are inherited. The needs of the organism influence structure. The spines in the quills in the tails of woodp.e.c.k.e.rs, and in the brown creeper, are other cases in point. The nuthatch has no spines on its tail, because it can move in all directions, as well with head down as with head up. I have read of a serpent somewhere that feeds upon eggs. As the serpent has no lips or distendable cheeks, and as its mechanism of deglut.i.tion acts very slowly, an egg crushed in the mouth would be mostly spilled. So the eggs are swallowed whole; but in the throat they come in contact with sharp tooth-like spines, which are not teeth, but downward projections from the backbone, and which serve to break the sh.e.l.ls of the eggs.
Radical or vital variations are rare, and we do not witness them any more than we witness the birth of a new species. And that is all there is to Natural Selection. It is a name for a process of elimination which is constantly going on in animate nature all about us. It is in no sense creative, it originates nothing, but clinches and toughens existing forms.
The mutation theory of De Vries is a much more convincing theory of the origin of species than is Darwin's Natural Selection. If things would only mutate a little oftener! But they seem very reluctant to do so. There does seem to have been some mutation among plants,--De Vries has discovered several such,--but in animal life where are the mutants? When or where has a new species originated in this way?
Surely not during the historic period.
Fluctuations are in all directions around a center--the mean is always returned to; but mutations, or the progressive steps in evolution, are divergent lines away from the center. Fluctuations are superficial and of little significance; but mutations, if they occur, involve deep-seated, fundamental factors, factors more or less responsive to the environment, but not called into being by it. Of the four factors in the Darwinian formula,--variation, heredity, the struggle, and natural selection,--variation is the most negligible; it furnishes an insufficient handle for selection to take hold of. Something more radical must lead the way to new species.
As applied to species, the fittest to survive is a misleading term.
All are fit to survive from the fact that they do survive. In a world where, as a rule, the race is to the swift and the battle to the strong, the slow and the frail also survive because they do not come in compet.i.tion with the swift and the strong. Nature mothers all, and a.s.signs to each its sphere.
The Darwinians are hostile to Lamarck with his inner developing and perfecting principle, and, by the same token, to Aristotle, who is the father of the theory. They regard organic evolution as a purely mechanical process.
Variation can work only upon a variable tendency--an inherent impulse to development. A rock, a hill, a stream, may change, but it is not variable in the biological sense: it can never become anything but a rock, a hill, a stream; but a flower, an egg, a seed, a plant, a baby, can. What I mean to say is that there must be the primordial tendency to development which Natural Selection is powerless to beget, and which it can only speed up or augment. It cannot give the wing to the seed, or the spring, or the hook; or the feather to the bird; or the scale to the fish; but it can perfect all these things. The fittest of its kind does stand the best chance to survive.
VI
After we have Darwin shorn of his selection theories, what has he left? His significance is not lessened. He is still the most impressive figure in modern biological science. His att.i.tude of mind, the problems he tackled, his methods of work, the nature and scope of his inquiries, together with his candor, and his simplicity and devotion to truth, are a precious heritage to all mankind.
Darwin's work is monumental because he belongs to the cla.s.s of monumental men. The doctrine of evolution as applied to animate nature reached its complete evolution in his mind. He stated the theory in broader and fuller terms than had any man before him; he made it cover the whole stupendous course of evolution. He showed man once for all an integral part of the zoologic system. He elevated natural history, or biology, to the ranks of the great sciences, a worthy member of the triumvirate--astronomy, geology, biology. He taught us how to cross-question the very G.o.ds of life in their council chambers; he showed us what significance attaches to the simplest facts of natural history.
Darwin impresses by his personality not less than by his logic and his vast storehouse of observations. He was a great man before he was a great natural-history philosopher. His patient and painstaking observation is a lesson to all nature students. The minutest facts engaged him. He studies the difference between the stamens of the same plant. He counted nine thousand seeds, one by one, from artificially fertilized pods. Plants from two pollens, he says, grow at different rates. Any difference in the position of the pistil, or in the size and color of the stamens, in individuals of the same species grown together, was of keen interest to him.
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