The Best Adventure and Exploration Stories Ever Told
Page 28
The tortoise begins by eating the coarse grass near its birthplace and, when they can be found, succulent pieces of cactus pads that have dropped from the arborescent cactus. At this stage of its life the little tortoise could be placed in a millpond anywhere and taken for a typical North American land tortoise. But in two years it loses its flatness; the shell, on the Indefatigable species, at least, begins to grow high and vaulted, so that the measurement across the shell is as much as its length. In the first years of its growth it appears to develop remarkably fast, as much as two inches a year. No one has ever followed this growth in the tortoise’s own habitat, the only records that exist are those kept in zoological gardens, and these records vary because of the superfluity of food in the zoos. In the Galápagos Islands it is different. Growth is strictly limited by scarcity or abundance of food.
Before man came to the Galápagos, the little tortoise had scarcely an enemy in the archipelago except its own clumsiness. Then man introduced pigs, dogs, cats, rats, goats, and mules. Today the tortoise must run the gamut of all these to survive. If it does survive, it continues to develop fairly rapidly until it is twenty-five years old, and then the rate is slowed down to a meager half-inch a year. Its life process is curious. The plastron or shell of the tortoise is not wholly solid. It is covered with hard, symmetrical, bonelike plates separated by nerve centers; at certain times of the year the nerve centers become white and then, one by one, the horny plates drop out. Underneath the detached plate is a new one. Each time this “moult” takes place, the new plate adds a centimeter in size. Such is the rate of growth of the tortoise, with the hard plastron beneath the skinlike plates keeping pace with the growth on the shell’s surface.
There are three diurnal phases to the tortoise’s life. It awakens at dawn and begins to search for food. If it happens to be on the lower slopes of the volcanic islands, it browses on cactus pads, which, although composed of 80 per cent water, have nonetheless, a fairly high nutritive content in starch and sugar. From them the tortoise gets both water and food. If the tortoise is on the higher zones of the islands, it browses on the green moss which covers the trees, or on the coarse grass. At noon, when it is warm, the tortoise retires for a siesta under the shade of the trees. Later in the afternoon it awakens again to eat until dusk, when it seeks out some dry spot upon which to sleep. No sooner is it dark than it is asleep; it does not, and will not, move far at night.
During the year, depending on the extent of the droughts (for those come sporadically to the Galápagos, depending on the caprice of the currents), there are numerous vertical migrations to the highest point of the islands. On some of the higher islands such as James, Indefatigable, Albemarle, and Narborough, water gathers in extinct volcanic vents during the rainy season, and the tortoises go up there to drink. They plunge directly into the water and drop their heads under the surface, completely submerge in fact, and gulp in the water. The liquid that is not absorbed into the system at once is stored in a large reservoir sac which rests on the lower part of the shell, within the carapace. This reserve is kept for those times when a great drought occurs in the islands. The early visitors to the Galápagos, whalers and pirates, soon learned of this water sac. They would cut open the tortoise and drink the water. The taste is slightly acrid, but that is of little importance when one is suffering from thirst. Darwin found that the vertical migrations to the top of the mountain were so frequent that the tortoises have worn smooth the lava rocks over which they dragged their mammoth carapaces.
The mating season changes this galápago monotony. Before the rains come, the male, who is, above all, placid and timid, changes his disposition. He becomes quarrelsome, opens his mouth, elongates his neck, and charges the first male that he encounters. Then he has voice—he bellows like a bull. The galapágo is polygamous; there are, in fact, no monogamous animals save those which mate only once during their lifetime.
In two months the cycle has ended, and the female, swollen with eggs, begins a search for the best place in which to cache her eggs. She hollows out a hole and expels the eggs into it. Then she scrapes the soil back into place over the cache and stamps with all her weight on the loosened earth, packing it solidly. Natives on the islands insist that the female purposely puts its excrement on top of the egg cache, stamping it down to create a cement-like surface. Then the eggs hatch, and the whole life cycle starts over again.
When the islands were first discovered, there were so many tortoises a sailor could walk for hundreds of feet on their shells without once stepping upon the ground. They were for the pirates a detectable food, as William Dampier says: “The land tortoises [are] so numerous that 500 to 600men might subsist on then alone for several months without any sort of other provision. They are so extraordinarily sweet that no pullets eat more pleasantly.
Every ship cruising in the Pacific during this time stopped for its quota of tortoises. It was the whaling era that began the fearful havoc among the galápagos. Dr. Townsend of the New York Aquarium estimated, after a perusal of whalers’ log books, that the number of galápagos taken from the islands by the whalers in thirty years exceeded 200,000. No one knows how many had been removed before that time. After 1850 every whaler that went into the Pacific stopped at the Galápagos for tortoises; on one of these boats was Herman Melville, who was sent ashore off the tip of Albemarle for tortoises. He writes in the Encantadas of seeing the men bring some of the species aboard the Acushnet:
“These mystic creatures, suddenly translated by night from unutterable solitudes to our peopled deck, affected me in a manner not easy to unfold. They seemed newly crawled forth from beneath the foundations of the world. Yet, they seemed the identical tortoises whereon the Hindu plants this total sphere. With a lantern I inspected them more closely. Such worshipful venerableness of aspect! Such furry greenness mantling the rude peelings and healing the fissures of their shattered shells. I no more saw three tortoises. They expanded, became transfigured. I seemed to see three Roman Coliseums in magnificent decay.”
“The little imps of darkness,” after the tortoises, commanded much of Darwin’s attention. These were the sea iguanas which animated the lava-bound littorals of all the Galápagos Islands. Darwin needed little to tell him that these long-tailed sea iguanas, which were named Amblyrhynchus cristatus, were utterly unique; they were the only living representatives of the extinct marine saurians. Finding then decidedly easy to observe, as was everything else on the Enchanted Isles. Darwin walked among the huge herds of seaweed-eating iguanas basking in the Galápagos sun. The smaller iguanas, as black as the lava stone on which they lay, would scurry before his large form like autumnal leaves hurrying before a breeze. Pausing after their dash, they would stop, snort sea water from their nostrils, and curiously look upon him who disturbed their reptilian reveries. The males, yellowish and orange spotted, reached an overall length of four feet. Given to a vigorous shaking of their heads—heads covered with pyramidal spikes such as once covered the ancient dragons—they appeared like palsied old gentlemen. They looked threatening, too the opened mouth revealing a range of sharp teeth and a soft, reddish, thick tongue. Short-legged and round-bodied, they moved quickly—always toward the sea when pursued—dragging their long tails behind them. Once in the water, they were at home. The front legs were clasped close to the scaled body, the hind feet hanging loosely, while the tail plied the water like the oar of a Venetian boatman. Darwin was the first to notice that the hind feet were webbed, but curiously enough, these webbed feet were not used for swimming; they hung loosely alongside the motive-power tail. A spined crest began at the neck and ran down the entire length of the body, lessening near the tail, yet continuing to its tip. Their sole diet was seaweed and the algae that covered the rocks and upon which they browsed when it was uncovered by the retreating tide.
Life was simple before man appeared. The huge masses of iguanas spread about the Galápagos shores had their lives planned in spheres of influence. Every ten or fifteen feet apart was a
n old male iguana. This was his territory and he dominated it and the females within it. If another male iguana made trespass upon it, they locked their heads in combat. Joining their spikes as bucks do their antlers, they would struggle across the lava, until, at last, one gave in and, shaking its head, moved away to another sphere. As among the tortoises, the mating season occurs in the month of January.
Charles Darwin, moving his tall frame among the clinkers of the Galápagos, then stumbled across yet another zoological phenomenon—distinctly Galápagoan—a land iguana to match a sea iguana. Nowhere else in the world are there two such distinct species of reptile, one confined to the sea and the other to land.
The land iguana is distinguished, among other things, from the sea iguana in that it cannot swim; its tail is shorter and more rounded; it is clumsier, plumper, and lacks the crest. Its head is longer and wider; the terminus or the snout of the reptile is rather pointed; the body is heavier; the color varies between intense canary yellow and brick red. It lives in deep holes that it hollows out in the loose soil by means of its heavy claws. There are so many of these caverns that as you walk about the island, you will suddenly feel the earth give way and you plunge into a nest of the lizards. On dull, misty days, they remain below in their nest; as soon as the sun’s warm rays have penetrated their homes, they crawl slowly up to the surface and lie in the sun’s rays, still numbed by the chill of the night. When their bodies are animated by the warmth, they start to browse on the cactus pads that have dropped from the bizarre Galápagos cactus, “dildoe tree.” With rare exceptions the cactus forms their only food; from it come both water and nutriment. They first scrape the more obtrusive thorns from the cactus with their claws, and then, with little more ado, clamp their jaws down on an ample portion; the head is thrown back and the throat muscles work the cactus into the stomach. The tongue, a soft, reddish organ, comes out of the side of the mouth and is either engaged in extracting water from the cactus by pushing it to the top of the mouth, or is merely getting out of the way of this thorned morsel.
The iguanas and their distribution rank as one of the most interesting of the Galápagos fauna puzzles. Darwin himself remarked that nowhere in the world, save at the Galápagos, would one find so well characterized species, “as the Conolophus and Amblyrhynchus, a genus having its terrestrial and marine species belonging to so confined a portion of the world.” At present it is not known whether the two distinct genera of marine and terrestrial iguanas “arrived” at the Galápagos already clearly and definitely characterized, or whether the land iguana evolved from the sea iguana. For the sea iguana is a powerful swimmer, and in view of this fact, its distribution on most of the islands is understandable. The land iguana, on the other hand, cannot swim. When placed in water its first attempt is to move its four legs, paddling like a dog. In a few minutes it ceases to move and allows itself to float on the water. Nor does it show an ability to breathe under water as does the sea iguana. Yet its habitats are on points of land in the Galápagos where the general currents of the Galápagos sea might have carried it. On the continents of Central and South America this particular species of iguana is found neither fossil nor living. It is not known where the land iguana came from or how it got to the Galápagos. As Charles Darwin walked the islands, scratching himself on the thorned acacias, filling his nostrils with the pungent smell of the palo santo tree, there was more on his mind than the tortoises. Item: the birds. He had expected to find here some of the gaudy inhabitants of the mainland jungles, cock-of-the-rocks, umbrella birds, toucans, and parrots; instead he found myriads of birds belonging more to a northern habitat than to the Equator. There were inquisitive mockingbirds, herons, petrels, finches, albatross, penguins (Galápagos penguins about which Herman Melville was to make pronouncement: “What outlandish beings are these? Erect as men; on land it stumps; afloat it sculls; in the air it flops”) oyster-catchers and lava gulls, doves which Darwin ate in a dove pie, a yellow-crowned night heron, a Galápagos green heron, which commanded the shore and played havoc with the fiery red graspus crab, two species of hawks, curious and tame, a species of owl, giant red-pouched boobies—and to add the only touch of color to the avian drabness—rookeries of scarlet-winged flamingoes, and a vermillion fly-catcher.
Darwin began the first collections of birds on the Galápagos and each skin that he prepared began all over again the questioning; it began to haunt him in his waking hours and in his sleeping hours. Eventually there were catalogued from the Galápagos 108 species and subspecies of birds, of which 89 are breeding and resident upon the isles, 77 confined exclusively thereto; but what impressed Darwin was not the uniqueness of the birds, but that living on isolated islets, they should still structurally follow the types from the American continent. On September 26, on Charles Island, he entered a significant note in his diary: “It will be very interesting to find from future comparison to what district or ‘centre of creation’ the organized beings of this archipelago must be attached.” Darwin had begun to collect and worry over a small dusky finch belonging to the family Geospizidae. He noted that the birds differed only in the variation of their beaks; some were sharp and long like that of the mockingbird, others humped and hocked in mimicry of the tick-hunting garrapatero of the continent. Many of these finches differed from island to island, each island ofttimes had its own species, as if they had been transformed to adapt themselves to special conditions. The same curious species differentiation was true of the giant tortoises. An English resident of Charles Island declared that the tortoises differed from the different islands, and that he could, with certainly, tell from which island any one was brought. At first Darwin confessed that he “did not pay sufficient attention to this statement and [he] had already partially mingled together the collection, from two of these islands. [He] never dreamed that islands, about fifty or sixty miles apart and most of them insight of each other, formed of precisely the same rocks, placed under a similar climate rising to a nearly equal height, would have been differently tenanted.”
“Differently tenanted.” The young naturalist’s mind began to recapitulate what he knew. The archipelago was geologically recent. It had, in his mind, recently (that is, geologically recently) arisen from the sea; it was separated from the mainland by only six hundred miles of water, yet so different were the creatures inhabiting the islands that they might have been a million miles away. Despite the uniqueness of the fauna, they had the basic characteristics of the animals of South America. Now, there were only two ways, in Darwin’s mind, to account for these resemblances and differences: either the tortoises, iguanas, and birds were “created independently, simultaneously, or successively, or they were derived from a common ancestry.” If the animals were created independently, the tortoises, for example, should in every sense, mimic their mainland counterparts. But they did not. Not only were there different species, but the species changed from island to island. If, on the contrary, all animals were descended from a common ancestry, one could explain their presence on the Galápagos, by some not yet discovered faunal migration, and that they differed from their continental prototypes because the factors of geographical isolation brought change. So, if the species found on the islands were not created especially for the islands, they must have been brought by wind, wave, or currents. If plant and animal species reached the Galápagos in this manner, why should they not have remained immutable?
Well, then, if the species were mutable and “subject to modification,” one would find that the Galápagos species were peculiar to them, yet showed more or less distinct relationship to those species on the mainland from which the Galápagos had originally received its species. This was the solution! If it applied to species of the Galápagos Islands, then it applied to the whole world of living things. How blind he had been! That was the answer. Geology proved it; paleontology confirmed it; and before his eyes, on the Galápagos, the very tortoises carried the solution on the backs of their shells, the finches in the shape of their beaks.
When Darwin returned to England after his five-year voyage, he published his Journal of the Voyage of the “Beagle.” And, at first, he put aside his hypothesis of the origin of living things. The material he had collected on the Galápagos was given to specialists to examine, and they, as curious as Darwin, kept asking new questions about the particular variations in his Galápagos collections.
The Enchanted Islands now began to haunt him. Relentlessly, he was driven toward the final statement of the whole problem of organic evolution.
The change became evident in 1844. His publishers asked him to revise his Journal of the Voyage of the “Beagle,” and, in doing so, he radically changed parts of the Galápagos chapter. Gone were the hesitations; the principal points of his Galápagos collections: “Aboriginal creations found nowhere else . . . differing from island to island . . . we are brought near to that great fact . . . the mystery of mysteries . . . the first appearance of beings on this earth . . . seeing this gradation of structure in one small intimately related group of birds (finches), one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.”
Already the color of his thought can be seen, “modified for different ends”; the investigations went on and always the Galápagos material lent him inspiration. Darwin was slow and methodical, the very antithesis of Herbert Spencer, of whom Huxley once said: “Spencer would regard as a tragedy . . . the killing of a beautiful theory by an ugly fact.”