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CHARLES DARWIN'S ACCOUNT OF GIANT TORTOISES ON THE GALAPAGOS ISLANDS

JUNE CHATFIELD, B.Sc., Ph.D., A.R.C.S.
The Oates Memorial Library and Museum and the Gilbert White Museum, The Wakes, Selborne, Alton, Hampshire GU34 3JH

BCG Symposium 1987

After a few terms studying medicine at the University in Edinburgh, followed by three years at Cambridge University training for the Church, Charles Darwin had the opportunity to join a voyage on the HMS Beagle round the world. He had shown a great interest in natural history at Cambridge where he came under the wing of Professor Henslow who directed his studies in geology and botany. Darwin attended the open house for undergraduates kept by Henslow and regularly joined him on field excursions. It was through Henslow that Captain Fitz-Roy wrote to Charles Darwin as a suitable young man to invite to accompany him as a naturalist on the voyage of HMS Beagle that included the Galapagos Islands off the north west coast of tropical South America. In his autobiography Charles Darwin stated that this voyage was the most important event in his whole life and it determined the rest of his career. On the journey, Darwin kept a very full and detailed Journal and from this he developed his book Journal of researches into the natural history and geology of the countries visited during the voyage of HMS Beagle round the world, now generally known as The Voyage of the Beagle. This was first published in 1839 as part of Fitz-Roy's work but Darwin's part has now been through many different editions.

The following extracts from the chapter on the Galapagos Islands describe the habitats and the giant tortoises for which the islands are famous. Darwin also used evidence from the variation in tortoises to support his new theory of evolution by natural selection published in his Origin of Species in 1859 that caused a considerable stir in Victorian society and the scientific world.

Extracts from The Voyage of the Beagle (Pages 57 to 62)

(1) Here Darwin gives a description of the islands visited in 1835:

(2) And now he encounters the giant tortoises:

(3) To the native inhabitants of the islands the tortoises were important as a staple source of meat and they also provided cash from their sale:

(4) Tortoise meat was salted for transport and when on James Island, Darwin ate tortoise meat too:

(5) He considered the reptile fauna of the islands as a whole, commented on the turtles and tortoises and pondered on the implication of the solid egg of the reptile in its zoogeography compared with amphibia:

(6) The tortoise then came in for more detailed treatment and Darwin took particular note of their habits and behaviour:

(7) The large tortoises left well beaten paths across the islands. It was also pointed out the unusual situation on the Galapagos Islands where the dominant vertebrates are reptiles rather than mammals:

(8) It was on the Galapagos Islands that Darwin developed his theory of evolution and he took particular note of the fact that each island had its own form of finches and tortoises, something which was already known to the inhabitants as his account shows:

The observations quoted in the following pages made Darwin reconsider the whole concept of what constitutes a species. Darwin's work on tortoises on the Galapagos Islands had implications in the more general field of zoological theory as well as providing detailed observations on those curious and spectacular reptiles, the giant tortoises.

REFERENCES

Chancellor, J, 1973: Chafles Darwin, George Weidenfield and Nichols.

Darwin, C., (First published 1839 - many editions since). Journals of researches into the natural history and geology of the countries visited during the Voyage of HMS Beagle round the world

Darwin, C. (First published 1859 - many editions since). The Origin of Species. Various publishers.

Darwin, F., 1929: Autobiography of Charles Darwin. Thinkers' Library, Watts & Co., London.

GALAPAGOS ARCHIPELAGO.

(1) Here Darwin gives a description of the islands visited in 1835:

September 15th.-This archipelago consists of ten principal islands, of which five exceed the others in size. They are situated under the Equator, and between five and six hundred miles westward of the coast of America. They are all formed of volcanic rocks; a few fragments of granite curiously glazed and altered by the heat, can hardly be considered as an exception. Some of the craters, surmounting the larger islands, are of immense size, and they rise to a height of between three and four thousand feel Their flanks are studded by innumerable smaller orifices. I scarcely hesitate to affirm, that there must be in the whole archipelago at least two thousand craters. These consist either of lava and scoriae, or of finely-stratified, sandstone-like tuff. Most of the latter are beautifully symmetrical; they owe their origin to eruptions of volcanic mud without any lava: it is a remarkable circumstance that every one of the twenty-eight tuff-craters which were examined, had their southern sides either much lower than the other sides, or quite broken down and removed. As all these craters apparently have been formed when standing in the sea, and as the waves from the trade wind and the swell from the open Pacific here unite their forces on the southern coasts of all the islands, this singular uniformity in the broken state of the craters, composed of the soft and yielding tuff, is easily explained.

Considering that these islands are placed directly under the Equator, the climate is far from being excessively hot; this seems chiefly caused by the singularly low temperature of the surrounding water, brought here by the great southern Polar current. Excepting during one short season, very little rain falls, and even then it is irregular; but the clouds generally hang low. Hence. whilst the lower parts of the islands are very sterile, the upper parts, at a height of a thousand feet and upwards, possess a damp climate and a tolerably luxuriant vegetation. This is especially the case on the windward sides of the islands, which first receive and condense the moisture from the atmosphere.

(2) And now he encounters the giant tortoises:

As I was walking along I met two large -tortoises, each of which must have weighed at least two hundred pounds: one was eating a piece of cactus, and as I approached, it stared at me and slowly stalked away; the other gave a deep hiss, and drew in its head. These huge reptiles, surrounded by the b1ack lava, the leafless shrubs, and large cacti, seemed to my fancy like some antediluvian animals. The few dull-coloured birds cared no more for me, than they did for the great tortoises.

(3) To the native inhabitants of the islands the tortoises were important as a staple source of meat and they also provided cash from their sale:

September 23rd. - The Beagle proceeded to Charles .Island. The inhabitants, although complaining of poverty, obtain, without much trouble, the means of subsistence. In the woods there are many wild pigs and goats; but the staple article of animal food is supplied by the tortoises. Their numbers have of course been greatly reduced in this island, that the people yet count on two days' hunting giving them food for the rest of the week. It is said that formerly single vessels have taken away as many as seven hundred, and that the ship's company of a frigate some years since brought down in one day two hundred tortoises to the beach.

(4) Tortoise meat was salted for transport and when on James Island. Darwin ate tortoise meat too:

October 8th. - We arrived at James-Island:

We found here a party of Spaniards, who had been sent from Charles Island to dry fish, and to salt tortoise-meat. About six miles inland, and at the height of nearly 2,000 feet, a hovel had been built in which two men lived who were employed in catching- tortoises, whilst the others were fishing on the coast. I paid this party two visits, and slept there one night. As in the other islands, the lower region was covered by nearly leafless bushes, but the trees were here of a larger growth than elsewhere, several being two feet and some even two feet nine inches in diameter. The upper region being kept damp by the clouds, supports a green and flourishing vegetation. While staying in this upper region we lived entirely upon tortoise-meat: the breastplate roasted (as the Gauchos do carne con cuero), with the flesh on it, is very good; and the young tortoises make excellent soup; but otherwise the meat to my taste is indifferent.

(5) He considered the reptile fauna of the islands as a whole, commented on the turtles and tortoises and pondered on the implication of the solid egg of the reptile in its zoogeography compared with amphibia:

We will now turn to the order of reptiles, which gives the most striking character to the zoology of these islands. The species are not numerous, but the numbers of individuals of each species are extra-ordinarily great. Of sea-turtle I believe there is more than one species; and of tortoises there are, as we shall presently show, two or three species or races. The absence of the frog family in the oceanic islands is the more remarkable, when contrasted with the case of lizards, which swarm on most of the smallest islands. May this difference not be caused by the greater facility with which the eggs of lizards, protected by calcareous shells, might be transported through salt-water, than could the slimy spawn of frogs ?

(6) The tortoise then came in for more detailed treatment and Darwin took particular note of their habits and behaviour:

I will first describe the habits of the tortoise (Testudo nigra, formerly called Indica), which has been so frequently alluded to. These animals are found, I believe, on all the islands of the Archipelago ; certainly on the greater number. They frequent in preference the high damp parts, but they likewise live in the lower and arid districts. I have already shown, from the numbers which have been caught in a single day, how very numerous they must be- Some grow to an immense size: Mr. Lawson, an Englishman, and vice-governor of the colony, told us that he had seen several so large, that it required six or eight men to lift them from the ground; and that some had afforded as much as two hundred pounds of meat. The old males are the largest, the females rarely growing to SO great a size: the male can readily be distinguished from the female by the greater length of its tail. The tortoises which live on those islands where there is no water, or in the lower and arid parts of the others, feed chiefly on the succulent cactus. Those which frequent the higher and damp re-iuns, cat the leaves of various trees, a kind of berry (called guayavita) which is acid and austere, and likewise a pale green filamentous lichen (Usnera plicata), that hangs in tresses from the boughs of the trees.

The tortoise is very fond of water, drinking large quantities, and wallowing in the mud. The larger islands alone possess springs, and these are always situated towards the central parts, and at a considerable height. The tortoises, therefore, which frequent the lower districts, when thirsty, are obliged to travel from a long distance. Hence broad and well-beaten paths branch off in every direction from the wells down to the sea-coast; and the Spaniards by following them up, first discovered the watering-places.

When I landed at Chatham Island, I could not imagine what animal traveled so methodically along well-chosen tracks. Near the springs it was a curious spectacle to behold many of these huge creatures, one set eagerly travelling onwards with outstretched necks, and another set returning, after having drunk their fill. When the tortoise arrives at the spring, quite regardless of any spectator, he buries his head in the water above his eyes, and greedily swallows great mouthfuls, at the rate of about ten in a minute.

The inhabitants say each animal stays three or four days in the neighbourhood of the water, and then returns to the lower country; but they differed respecting the frequency of these visits. The animal probably regulates them according to the nature of the food on which it has lived. It is, however, certain. that tortoises can subsist even on those islands, where there is no other water than what falls during a few rainy days in the year.

I believe it is well ascertained, that the bladder of the frog acts as a reservoir for the moisture necessary to its existence: such seems to be the case with the tortoise. For some time after a visit to the springs, their urinary bladders are distended with fluid, which is said gradually to decrease in volume, and to become less pure. The inhabitants, when walking in the lower district, and overcome with thirst, often take advantage of this circumstance, and drink the contents of the bladder if full; in one I saw killed, the fluid was quite limpid, and had only a very slightly bitter taste. The inhabitants, however, always first drink the water in the pericardium, which is described as being best.

The tortoises, when purposely moving towards any point, travel by night and day, and arrive at their journey's end much sooner than would be expected. The inhabitants, from observing marked individuals, consider that they travel a distance of about eight miles in two or three days. One large tortoise, which I watched, walked at the rate of sixty yards in ten minutes, that is, three hundred and sixty yards in the hour, or four miles a day,-allowing a little time for it to eat on the road. During the breeding season, when the male and female are together, the male utters a hoarse roar or bellowing, which, it is said, can be heard at the distance of more than a hundred yards. The female never uses her voice.. and the male only at these times; so that when the people hear this noise, they know that the two are together. They were at this time (October) laying their eggs. The female,where the soil is sandy, deposits them together, and covers them up with sand; but where the ground is rocky she drops them indiscriminately in any hole: Mr. Bynoe found seven placed in a fissure. The egg is white, and spherical; one which I measured was seven Inches and three-eights in circumference, and therefore larger than a hen's egg. The young tortoises, as soon as they are hatched, fall a prey in great numbers to the carrion-feeding buzzard. The old ones seem generally to die from accidents, as from falling down precipices: at least several of the inhabitants told me, that they had never found one dead without some evident cause.

The inhabitants believe that these animals are absolutely deaf- ; certainly they do not overhear a person walking close behind them. I was always amused .when overtaking one of these great monsters, as it was quietly pacing along, to see how suddenly, the instant I passed, it would draw in its head and legs, and uttering a deep hiss fall to the ground .with a heavy sound, as if struck dead. I frequently got on their backs, and then giving a few raps on the hinder part of their shells, they would rise up and walk away;-but I found it very difficult to keep my balance.

The flesh of this animal is largely employed, both fresh and salted ; and a beautifully clear oil is prepared from the fat. When a tortoise is caught, the man makes a slit in the skin near its tail, so as to see inside its body, whether the fat under tile dorsal plate is thick. If it is not, the animal is liberated; and it is said to recover soon from this strange operation. In order to secure the tortoises, it is not sufficient to turn them like turtle, for they are often able to get on their legs again.

There can be little doubt that this tortoise is an aboriginal inhabitant of the Galapagos ; for it is found on all, or nearly all, the islands, even on some of the smaller ones where there is no water; had it been an imported species, this is .would hardly have been the case in a group which has been so little frequented. Moreover, the old Bucaniers found this tortoise in greater numbers even than at present; Wood and Rogers also, in 1708, say that it is the opinion of the Spaniards, that it is found nowhere else in this quarter of the world. It is now widely distributed ; but it may be questioned ,whether it is in any other place an aboriginal. The bones of a tortoise at Mauritius, associated with those of the extinct Dodo, have generally been considered as belonging to this tortoise; if this had been so, undoubtedly it must have been there indigenous; but M. Bibron informs me that he believes that it was distinct, as the species now living there certainly is.

(7) The large tortoises left well beaten paths across the islands. It was also pointed out the unusual situation on the Galapagos Islands where the dominant vertebrates are reptiles rather than mammals:

As I at first observed, these islands are not so remarkable for the number of the species of reptiles, as for that of the individuals; when we remember the well-beaten paths made by the thousands of huge tortoises-the many turtles-the great warrens of the terrestrial Amblyrhynchus-and the groups of the marine species basking on the coast-rocks of every island-we must admit that there is no other quarter of the world where this Order replaces the herbivorous mammalia in so extraordinary a manner.

(8) It was on the Galapagos Islands that Darwin developed his theory of evolution and he took particular note of the fact that each island had its own form of finches and tortoises, something which was already known to the inhabitants as his account shows:

I have not as yet noticed by far the most remarkable feature in the natural history of this archipelaglo; it is, that the different islands to a considerable extent are inhabited by a different set of beings. My attention was first called to this fact by the Vice-Governor, Mr. Lawson, declaring that the tortoises differed from the different islands, and that he could ,vith certainty tell from which island any one was brought.

The inhabitants, as I have said, state that they can distinguish the tortoises from the different islands ; and that they differ not only in size but in other characters. Captain Porter has described ' those from Charles and from the nearest island to it, namely, Hood Island, as having their shells in front thick and turned up like a Spanish saddle, whilst the tortoises from James Island are rounder, blacker, and have a better taste when cooked. Mr. Bibron, moreover, informs me that he has seen .what he considers two distinct species of tortoise from the Galapagos, but he does not know from which islands.

The specimens that I brought from three islands were young ones ; and probably owing to this cause, neither Mr. Gray nor myself could find in them any specific differences.

Dr. Hooker He remarks that this law of distribution holds good both with those genera confined to the archipelago, and those distributed in other quarters of the world; in like manner we have seen that the different islands have their proper species of the mundane genus of tortoise, and of the widely distributed. American genus of the mocking thrush, as well as of two of the Galapageian subgroups of finches, and almost certainly of the Galapageian genus Amblyrnynchus.

But it is the circumstance, that several of the islands possess their own species of the tortoise, mocking-thrush, finches, and numerous plants, these species having the same general habits, occupying analogous situations, and obviously filling the same place in the natural economy of this archipelago, that strikes me with wonder. It may be suspected that some of these representative species, at least in the case of the tortoise and of some of the birds, may hereafter prove to be only well-marked races; but this would be of equally great interest to the philosophical naturalist.

END

Testudo Volume Two Number Five 1987

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