The Tests of Evolution: Naturalist at Large
by THOMAS BARBOUR
1
I THINK there is more misunderstanding about evolution among laymen than about any other subject. Of course we know that some fundamentalists still deny it. I am not writing for them, but rather for those who have been led to believe that the whole subject is settled and that “scientists know all about it,”which is quite untrue. The results of evolutionary processes are everywhere easy to see, but the situation is really like that of the man who sees a trolley car for the first time. The route it has followed and the direction in which it is going are clearly to be seen, and the rate at which it progresses is obvious. But what makes the thing move?
Take such a stock as that of the horse, where the fossil evidence is unusually good. Practically every single gradation from the little fox-terrier-like animal of thirty million years ago to the present-day horse may be followed with infinite elaboration of detail. The horse had its origin in the New World and we know when it moved from the New World to the Old, where it persisted in the form of the zebras, wild asses, and wild horses of Tibet. The skeletal remains show that horses, as we use the word today, existed in Florida down to perhaps 10,000 years ago in unbelievable numbers. Then they died out. Why they died out remains a mystery. The Spaniards brought horses with them from Europe and enlarged them — that is, turned them loose — and in no time they became enormously abundant again. Few laymen know that the camels originated in America and went through most of their evolutionary history in what is now the western part of the United States. During the height of the glacial period enough oceanic water was tied up in the gigantic polar icecap to lower the level of the oceans, so that many land areas now separated by water were then connected. Thus the camels reached the Old World and the elephants reached the New; and strangely enough, according to a Russian scholar, Naxonoff by name, the sheep not only passed from Asia to North America but went back again, leaving the ancestors of all our various species of bighorn behind them.
Geologically speaking, a fairly recent uplift of land formed Central America (for the Caribbean Sea was once a bay of the Pacific) and allowed camels to reach South America, where they persist as the llama, alpaca, guanaco, and vicuña. The stock then died out in North America. The elephants pushed down as far as Ecuador and likewise disappeared, as they did all over North America, where they once existed in countless numbers of individuals and an unbelievable variety of species.
I can hear my reader ask, “How do you know that the Caribbean was once a bay of the Pacific?" The answer was given by Alexander Agassiz during his explorations with the steamship Blake. He found that there was a greater difference between the deep-water fauna on the inside and that on the outside of the arc of Lesser Antillean islands than there was between the fauna inside the are and that on the Pacific side of the Isthmus of Panama. Only last year I described a lovely rosy Chaunax, a chubby, pothellied deep-sea fish which had its only near ally in one described from the Bay of Panama, and my fish came from the south coast of Cuba in a thousand fathoms of water.
2
Unfortunately the lines, “Some call it Evolution, And others call it God,” however true they may be, savor of the trite and the smug. No one who thinks and has had a real chance to study modern paleontological material doubts the fact of evolution, but the mystery behind it all is deep and dark and as worthy of our worship, if you will, as it ever was. Scientists have seen the evidence where evolution has run riot. The dinosaurs reached a size which was mechanically disadvantageous. The Irish elk proceeded to produce such gigantic horns (which presumably were dropped each year) that their very renovation from year to year must have involved a fatal weakening of the stock, which of course has long since disappeared. Cope had a phrase for this process, and a good one, too. It was “superabundant growth force” — growth in a particular direction until it becomes lethal.
But what brings this force into being? Darwin provided a couple of useful slogans — “sexual selection,” “the struggle for existence,” and Spencer added “the survival of the fittest.”
Each one of these explains a good deal. But let us apply it, for instance, to the leaf butterfly and see just how much it helps us. Metaphorically speaking, a racial stock of butterflies for its own protection starts out to become deadleaf-like. If this change were to be accomplished by natural selection alone, it would be reasonable to suppose that as soon as the butterflies became sufficiently leaf-like to be protected the evolution would cease. It did no such thing. The leaf butterflies of the Old World are decorated with marks such as the fungi of decay produce on dead leaves, and have ragged wing margins which look like wearings or tearings in some cases. In other words, they have become ridiculously and unnecessarily dead-leaf-like. Something pushed the evolutionary urge along far beyond necessity.
Lamarck postulated the evolutionary power of use and disuse and believed that acquired characters might be inherited. We all know, however, that certain sections of the human race have mutilated themselves for thousands of generations without result, and we know that in the old days when horses’ tails were regularly cut short, no short-tailed colts ever appeared.
As a matter of fact, to be realistic in our appreciation of evolution we have to be willing to say, “I don’t know how or why, but it is there just the same.” We have to avoid believing in what may seem to be too obvious. Consider how fearful the ordinary person is of inbreeding. Such and such animals are inbred; hence they are weak, stupid, deformed, or what have you. As a matter of fact, animals may be successfully bred for countless generations, brother to sister, if nothing but completely sound stock is used to breed from. Of course one abnormal individual may upset the strain and bad results will then appear, but the bad results do not come from the inbreeding.
I have recently been studying a group of fishing frogs, deep-sea fishes in which the first element of the dorsal fin has been developed into a fishing rod. In some of the fish this is capable of motion and may be moved out in front of the fish’s mouth and waved about, the tip of the ray being beset with little movable filaments which are fished about, squirming like a worm on a hook, to lure small fish up and into the mouth of the Antennarius.
This group of fishes is enormous, and in some species we see all sorts of ridiculous things which have happened — cases where a rod persists as only a useless filament incapable of motion, cases where it is elaborated into an organ so complicated and so absurd that it is hard to believe that it is anything but an ornament, using the word in its zoological sense. The creature couldn’t possibly get that great branching affair into its mouth. Some of these fishing frogs are just gigantic muscular sacs with fins so degenerated that obviously the creatures cannot move. They have great cavernlike mouths, not improbably suffused with a luminous slime to lure fish to a point where, with a sudden gulp, they can be engulfed by these animated muscular sacs.
Many of the baits at the end of the fishing rods are luminous, and some rods are long enough so that this luminous bait can be pushed right around and into the fish’s mouth. Then he snaps on the electric light, the little fish come up inquisitively, he snaps it out of the way, the mouth closes, and our fishing frog is fed.
3
I cite the extraordinary example of evolution presented by the fishing frogs because to me it is absolutely impossible to see how the first step ever happened to take place; it is simply not explainable by any means at our command. The fishing rod had to be a good fishing rod before it served the fish any useful purpose at all. Now explain that if you can.
This discussion may sound a little old-fashioned to a modern specialist. Recent authors, among them Richard Benedikt Goldschmidt of the University of California and Ernst Mayr of the American Museum of New York, have written fascinating books concerning the modern interpretation of microand macro-evolution. The light which modern genetics has thrown on evolution has been carefully appraised; moreover, what it may be expected to interpret in the future has not been neglected. Genetics has thrown light, and a flood of light, on heredity and the mechanism of inheritance.
This is a very different thing from throwing light on transformism, which is evolution. Mayr has shown that the systematic zoologists, or the taxonomists, with, of course, the paleontologists, are the ones who have made the most extensive contributions to our knowledge. Whether they wall continue to do so in the future remains to be seen.
But the sum total of what is really new is not greater than the contribution to knowledge made by Hugo de Vries in 1901, and nothing like so illuminating as the restatement of Jordan’s Law of Evolution through Isolation — which I am about to quote in the words of Tate Regan. He has pointed out in t hose meaty paragraphs that this isolation might be geographic or habitudinal: —
“This theory [that is, the mutation theory], which explains adaptation as the result of a series of fortunate accidents, appears to me to approximate to the old ‘special creation’ theory, and it was in opposing this idea of great and sudden transformations that Darwin wrote: ‘To admit all this is, as it seems to me, to enter into the realms of miracle and to leave those of science.’ The mutation theory is in favour with the geneticists, who have found that definite variations occur and are definitely inherited. But the geneticists are puzzled to suggest how these variations could become specific characters, common to all the members of a species, seeing that they are not adaptive, and therefore could not be selected.
“Systomatists attach little importance to interspecific sterility; they know that Darwin showed that between allied species there are all gradations, from complete sterility to complete fertility. But for the geneticists sterility is all-important — it is their one hope of producing the semblance of a species — and they proclaim that the event for which they are waiting is the production of a variety which is sterile with the parent form. That great event, if and when it occurs, will leave me cold; in my opinion, it will have about as much relation to the origin of species as the occurrence of albinos has to the coloration of arctic animals — that is to say, no relation whatever!
“My own work,” Tate Regan continues, “on the structure, classification, and geographical distribution of fishes has led me to certain conclusions. I believe that the first step in the origin of a new species is not a change of structure, but the formation of a community, either through localization, geographical isolation, or habitudinal segregation. I also think that specific characters may be grouped as follows: they are either (a) useful, (6) correlated with useful characters, (c) due to the environment, or (d) the expression of some physiological peculiarity. But I see no reason for believing that they have originated as mutations.”
As I said before, we encounter a multitude of mysteries in the study of evolution, and these have made me a little bit impatient and uncharitable toward the atheist. As man’s know ledge of the mysteries expands, their magnitude increases and leaves the honest and candid man very humble in mind.
I don’t see why anyone should gag at the consulship of man and the apes — the relationship is too distant. Rather let him consider with awe the majesty of orderliness which to the humble-minded is the subject most to be respected within man’s ken. Like the concept of infinity in time or space, this matter passes our understanding.