The Other Islands of Charles Darwin

by Patrick Armstrong, Department of Geography, University of Western Australia

Everyone knows Charles Robert Darwin (1809-1882) recognised how the birds and reptiles differed from one island to another in the Galapagos. But years before he set foot on the archipelago he was making similar observations in the Falkland Islands. He noticed that the foxes of East and West Falkland differed in fur colour and size as well as foreseeing the imminent extinction of this extremely tame animal. He was right as the last one was killed less than 50 years after his visit.

Late in life Darwin wrote the following in his autobiography - a short work intended primarily for members of his family:

During the voyage of the Beagle I had been deeply impressed by the South American character of most of the productions of the Galapagos archipelago, and more especially by the way in which they differ slightly on each island of the group, none of these islands appearing very ancient in a geological sense.

In writing these words he was giving rise to the legend that he had been converted to an evolutionary view by a ‘eureka-like’ experience that took place while he was on these islands. It became a legend that to some extent was shared by Darwin himself in later years.

In fact, it is clear from a careful study of his notes (now in the Darwin Archive at Cambridge University Library) that while the experience of the 19 days (including several part-days) that the young naturalist (he was only 27) spent ashore on four of the Galapagos islands during September and October 1835 were important, they were certainly not all-important. Darwin’s ‘conversion’ to an evolutionary outlook, if such it were, was more gradual. If a moment of particular insight has to be singled out, it might have been mid-March 1837, when Darwin was discussing his specimens with “the leading scientific men” in London.

Darwin visited dozens of islands during the five years (table 1) he was aboard HMS Beagle and many of them were important in his intellectual development. It seems that islands in general held a particular fascination for him and, from an early point on the Beagle voyage, he was structuring and arranging his observations in ways that demonstrated themes which were later to prove important.

In the field Darwin made brief pencil notes in his “little note books” and these formed the basis of more expansive accounts that he wrote up at leisure, perhaps in the evenings, at the table of the poop cabin, with his specimens, instruments and reference books around him. Often he wrote additional notes in the margins, comparing his observations with what he saw later in the voyage, or with those of other observers, for he had with him on the Beagle the writings of dozens of earlier navigators and explorers. Occasionally he completely rewrote his notes, in some instances several times, as new information came to hand, or as he revised his opinions. It is thus possible to trace the way in which he changed his ideas during the course of his travels.

Darwin’s method of working was thus comparative and cumulative. Indeed, it may be said that this comparative approach (which he may have gained from his reading of J F W Herschel [1792-1871] Discourse on the Study of Natural Philosophy while an undergraduate) and constant reassessment of material provided the key to his success. Nowhere did this comparative method have a fuller reign than in the way he observed the natural history of, and wrote about, the many islands he visited during the voyage of the Beagle.

The islands that never were

One of the most important islands in Darwin’s development was one upon which he never actually set foot. In the late spring and early summer of 1831, Darwin, his teacher J S Henslow (1796-1861), and one or two other Cambridge associates planned an expedition to Tenerife in the Canaries. The proposal seems to have been inspired by the young Darwin’s reading of Alexander von Humboldt’s Personal Narrative of Travels to the Equinoctial Regions of a New Continent, which had a great effect on him.

Although this particular venture was superseded by Darwin’s invitation to go on the Beagle voyage, it was the planning of the Tenerife project, the learning of Spanish that summer, and the reading of Humboldt that got Darwin into an appropriate frame of mind for the much more important expedition in which he actually took part. He was thus devastated when coming into sight of Tenerife at daybreak on 6 January 1832, with the peak just above the clouds and “the colours so rich and soft”, that they were not allowed to land because of quarantine regulations.

There was another incident in the voyage that concerns ‘islands that never were’. In his diary for 3 January 1832, three days before the ill-fated call at Tenerife, Darwin wrote:

We looked for the eight stones and passed over the spot where they are laid down in the charts. Perhaps their origin might have been volcanic and have since disappeared.

Whether this was the correct explanation or not, the fact that Darwin considered it just a week into the voyage shows that he was aware of the transient nature of some islands, and that he lived in a dynamic, changing world.

Volcanic Islands

Here is Darwin’s recollection of his visit to St Jago, in the Cape Verde Islands, about ten days after the Beagle’s abortive call at Tenerife:

The geology of St Jago is very striking yet simple: a stream of lava formerly flowed over the bed of the sea, formed of triurated recent sands and corals, which it has baked into a hard white rock. Since then the whole island has been upheaved. But the line of white rock revealed to me an important fact, namely that there had been afterwards subsidence round the craters, which had since been in action and poured forth lava. It then dawned on me that I might perhaps write a book on the geology of the various countries visited, and this made me thrill with delight. This was a memorable hour for me, and how distinctly I can recall the low cliff of lava beneath which I rested, the sun glaring hot, a few strange desert plants growing near, with living corals in the tidal pools at my feet.

Clearly Darwin’s first experience of a tropical island was of importance to him. Here he could see how the world was continually changing and how the geologist could reconstruct these changes from the rocks. Here within a very short distance were living corals, coralline fossils in limestone, and that limestone metamorphosed by contact with lava. Here was evidence for both uplift and subsidence, volcanic activity and sedimentary deposition. Here too was pattern amidst complexity.

Later he visited Mauritius, the Galapagos, Terceira in the Azores, New Zealand and Ascension, comparing their external forms and the minerals in the rocks of which they were formed. Darwin developed ideas about how a range of volcanic rock types could develop from a single source and how a volcanic district went through something of a life-cycle. He was far ahead of his time, putting forward many ideas that were later shown to be of importance. After visiting Terceira, the Beagle sailed along the coast of the elongate island of Sao Miguel. Upon his return to England he examined maps and charts and was struck by the alignment of volcanic cones on individual islands as well of islands in archipelagos. Here is a quotation from his book Volcanic Islands written shortly after his return from the voyage:

The composition of the numerous islands, scattered through the great oceans, being with rare exceptions volcanic, is evidently an extension of that law, and the effect of those same causes, whether chemical or mechanical, from which it results that in the vast majority of the volcanoes now in action, stand either as islands in the sea, or near its shores. The fact of ocean islands being so generally volcanic, is, also, interesting in relation to the nature of mountain chains on our continents, which are comparatively seldom volcanic; and yet we are led to suppose, that where our continents now stand, an ocean once extended. Do volcanic eruptions, we may ask, reach the surface more readily through fissures formed during the first stages of the conversion of the ocean into a tract of land?

No, Darwin was not about to expound the modern notion of plate tectonics, but in appreciating the linear nature of what are now called island arcs, and appreciating that these were associated with major fracture systems in the ocean bed, and that these alignments were in some way associated with the continual change in the distribution of land and ocean on the earth’s surface, he was not so very far away.

The coral atoll theory

The development of Darwin’s “Theory of coral reefs and atolls” - the notion that fringing reefs, barrier reefs and atolls are members of a continuous series, one form gradually passing into another through the subsidence of an island - is also testament to his comparative approach. In his geological and zoological notes from the visits to Tahiti and the Cocos Islands we can see his eye for detail, for example, in the way that he observed how each species of coral had its niche in the reef structure as a whole. Some were found on the turbulent outer reef, some closer inshore, some in the quiet waters of the lagoon.

The first coral atoll Darwin appears to have glimpsed, apparently from the masthead, was as the ship swept through the “Low or Dangerous Archipelago” en route from the Galapagos to Tahiti in November 1835. At Tahiti he explored coral reefs for the first time, occasionally from a small boat. He also saw the island of Eimeo (now Moorea) from a mountain.

Darwin had already seen what he believed to be changes in the level of the sea in relation to the land in South America and the Falklands. Later, from fieldwork in New Zealand, Australia and on other islands, he had confirmation of the fact that changes had occurred in the relative levels of land and sea. By the time he arrived in the Cocos (Keeling) Islands in April 1836 (the first and only time he actually set foot on an atoll), his ideas were well formed. His observations there confirmed his earlier ideas.

From Cocos the Beagle crossed the Indian Ocean to Mauritius and from 29 April to 9 May 1836 Darwin was able to walk, or ride, around a good deal of the northern coast of the island. Here he was able to find evidence for the elevation of reefs. Thus, through his comparison of a range of coral islands and other environments over a period of many months, Darwin was able to build a coherent theory. This was important, as the notion that one form of coral island might pass into another as the result of changes in the relative levels of land and sea represented one of his first flirtations with the ideas of gradualism - the significance of gradual change.

A refuge for the destitute

Charles Darwin used the term “refuge for the destitute” for the Cocos Islands. In it we see both the idea that the biota of remote islands is extremely depauperate and that of an assemblage of plants and animals thrown together as the result of long and difficult journeys. He was struck by the poverty of the Cocos flora: “the number of native plants is exceedingly limited”. The same applied to the animal kingdom: “There are no true land birds... Insects are very few in number”. He compared the poverty of the land biota with the fecundity of the nearby coral reef. “Although the productions of the land are scanty” he was later to write, “if we look at the surrounding sea, the number of organic beings is indeed infinite”. Interestingly, earlier in the voyage he had made a similar comparison between the biological poverty and desolation of the Falklands with the richness of the adjoining kelp beds. Significantly, too, he also compared the barrenness of East Falkland as it is now with the abundance and productiveness that existed in the remote past, for he had found a rock stratum that was packed with fossils.

Darwin speculated about the manner in which organisms reached remote islands. While at Cocos he noticed the way in which coconuts, seeds and other plant material were washed up along the shore. In the Falklands he compared the plants and invertebrates with those of nearby South America. He wondered if “the SW furious gales” might have blown tiny fragments of life across. These speculations were important for they later were found to fit well with his evolutionary ideas. If all living things on earth were derived from a single form, or a few simple original forms, then all plants and animals living on a remote island must have been carried thither in some way. Long distance dispersal was the handmaiden of evolution.