Posts Tagged 'book review'

The Voyage of the Beagle – Species and Change

When the Beagle expedition set sail in 1831, the great majority of English natural philosophers believed that each species of plant, animal, even microorganism was a unique and direct result of divine creation.  Given the unknowable purpose of the Creator, a human person could not predict what sorts of creatures would be found as the European explorers fanned out across the earth.  Certainly the outrageous variety of the planet’s creatures seemed consistent with such divine unpredictability.  For Charles Darwin, there was no counterpart of Charles Lyell’s Principles of Geology for the living world, to explain this living material in terms of material causes.  He had instead William Paley’s books, particularly Natural Theology (or Evidence of the Existence and Attributes of the Deity, collected from the appearances of nature), which were so widely accepted as conventional wisdom in English society as to be an essential element of Cambridge University education (I will review Natural Theology in a later post).  Charles took uncharacteristic interest in Paley’s books, no doubt because they spoke to his passion for natural history.  His Cambridge mentor, Professor John Stevens Henslow, and the Beagle’s captain, Robert FitzRoy, wholeheartedly embraced Paley’s explanations in terms of direct divine creation of each species.  According to Alan Moorehead’s account in Darwin and the Beagle (page 37), FitzRoy urged a very willing Darwin to use the voyage as a grand opportunity to substantiate the Bible, particularly the book of Genesis – looking for evidence of the Flood and the first appearance of all created things upon the earth – performing a valuable service by interpreting their scientific discoveries in the light of the Bible.

 

Linnaeus and the Collecting Imperative

 

Divine creation gave supreme importance to species as distinct entities presumed to be unchanged since their creation, much as the physical world was assumed to be now as it always was.  The great project for naturalists was to discover, describe, and catalogue these species, as a testament to the work of God.  Carl Linnaeus, of Sweden, less than a century before, had gathered the existing catalogues of species into a rational system of classification that serves us still.  The Linnaean system groups species into larger categories of similar organisms – genus, family, order, class, phylum, and kingdom.  It is significant that this systematic grouping subtly contradicts the notion of divine unpredictability by its implicit acknowledgment of relatedness among species.  Relatedness implies kinship, which means descent from a common ancestor.  The Linnaean system is built from a platonic notion of the species as a divinely created archetype, which is manifested in the real world as living creatures with some imperfect variation from the perfect archetype.  The archetypes bear no necessary relationship to one another, other than all being created by the same Creator.  However, the relatedness embedded in this classification system invites us to associate the species idea with individual humans related by descent from a common ancestor or with breeds of domestic plants and animals that can be traced back to common ancestors in the wild.  It is only a small step from Linnaeus to a notion of new species developing from existing species rather than directly from God. 

 

The Linnaean system of classification energized those with a natural bent for collecting, because his system gave a unique name to each existing species and established rules for naming and describing newly discovered species (and for giving recognition in perpetuity to the first person to do so for each new species!).  Linnaeus established the rules of a game many people were eager to play, including Charles Darwin and also Captain FitzRoy and a few other members of the Beagle crew.  They were schooled in the techniques for preserving specimens of species for description and naming and storage for posterity by expert curators of the British Museum or university museums or private collections.  A scientific voyage like the Beagle’s was expected to bring back to England a rich trove of specimens of species from across the full range of life on earth.

 

Charles’ shooting skill and physical fitness served this collecting imperative very well.  He also had lots of help from his servant, Sims Covington, and others of the crew or local people hired to guide his travels inland.  The collectors’ determination is exemplified in a passage of Charles’ Journal of Researches about his foray into the Brazilian rainforest near Rio de Janeiro.  One of his party shot a howler monkey dead as its prehensile tail was wrapped tight around a limb high in one of the taller forest trees.  The poor monkey’s body hung by its tail, frozen in a death grip on the tree limb.  Not to be so easily thwarted, they felled the enormous tree with their machetes, just to secure the prize specimen.  After a couple of years of avid pursuit of such specimens, ranging from the minute to the enormous, Charles found his geological hammer more in keeping with his focus on geology than his guns, which he handed over to Covington for the work of shooting birds, mammals, and other fast-moving creatures.

 

The Argentine Fossils — Species Replacing Other Species Over Time

 

On the low bluffs of the seashore and river banks of Argentina, Charles made discoveries that straddled his interests in geology and biology.  In the deeper layers of ancient sediment, Charles found the fossil remains of giant mammals vanished from the earth thousands of years before – they were not unlike the present-day sloths, armadillos, and guanaco, but much more massive.  Other fossilized remains resembled elephants and hippopotamus, which no longer live in the Americas.  He even found a fossil horse, showing that horses once roamed these plains and then became extinct long before horses were reintroduced to the New World by the Spanish. 

 

Extinction poses a problem for understanding divine creation of species.  Why would a species created by God be so imperfect as to go extinct?  Captain FitzRoy and others had answers in keeping with the Biblical story – for example, some species just did not make it onto Noah’s Ark in time, the larger species being the harder to accommodate.  If their answers seem forced, it is because they had to acknowledge somehow the fossil evidence of extinction; a rich assortment of fossils of now extinct animals and plants had been known for decades in Europe.  These fossil giants of Argentina added some spectacular new evidence, but they were significant mainly as direct personal confirmation for Charles that the species we see here and now are not all the same as the ones we would have seen thousands of years before in this same location.  Fauna and flora, like the geology, change over time.

 

The layer or stratum in which each fossilized animal is embedded tells a story of the environment of that animal in its own time, and Charles figured from the fossil-bearing strata that climate and vegetation then were similar to the present.  Therefore, the extinction could not be explained by catastrophic or even gradual geological or climate change.  Charles thought at first that species, like individuals, might have “a fixed and determined length of life” beyond which they would lose their vigor and go extinct.  Even if this were true (which it is not), Charles found it curious indeed that the giant mammals had been replaced over time by similar species, but almost all of much smaller stature.

  

Two Rheas — One Replaced the Other as Charles Traveled South

 

Charles devoted long passages of his Journal of Researches to description of the animals he encountered, often drawing from reports of local people and his own observations of their behavior and ecology.  One animal he was particularly taken with was the “ostrich” (now called the rhea) of South America.  Actually, there were two species, one of which was later named darwinii after Charles himself, from a specimen he pieced together from the remains of a bird his party had shot for food and mostly eaten by the time Charles realized this was the rarer species reported by his guacho companions.  Most interesting to Charles was that the common rhea of the pampas gave way to Darwin’s rhea in Patagonia, the dividing line being around the Rio Negro at 41º South – one rhea species rather abruptly replacing the other going south, yet the landscape and ecology changed only very gradually.  

 

Isolated Archipelagos — No Fear Where No Man Has Been 

 

First in the Falkland Islands and much later in the Galapagos, Charles was amazed by the tameness of the land birds of these islands – that is, the birds were unafraid of people, allowing themselves to be approached closely and even touched (or killed with a stick).  He noted that “of the few archipelagoes of any size, which when discovered were uninhabited by man, these two are among the most important.”  He also noted that “Few young birds in England have been injured by man, yet all are afraid of him: many individuals, on the other hand, both at the Galapagos and at the Falklands, have been injured, but yet have not learned that salutary dread.”  Charles concluded that fear of humans is a particular instinct directed at humans, not just part of a general caution arising from other sources of danger.  He also concluded that fear of humans “is not acquired by them in a short time, even when much persecuted; but that in the course of successive generations it becomes hereditary.  With domestic animals we are accustomed to see instincts becoming hereditary; but with those in a state of nature, it is more rare to discover instances of such acquired knowledge.”  It seems to me this remarkable passage gets insufficient notice in works on Darwin’s development of the theory of evolution.  Yet here already is a sound understanding of change within a wild species due to a new challenge in the environment of the species, much like the change brought about by selective breeding of domestic animals for various physical and behavioral traits.

 

Islands and Mainlands and the Species Problem

 

 

The Galapagos Islands are more associated in the public mind with Charles Darwin and the voyage of the Beagle than any other stopover of the five-year expedition, yet the Beagle spent barely more than a month exploring this archipelago and might have skipped the islands altogether in the crew’s eagerness to return home.  This distorted perception reflects the uniqueness of the Galapagos and its fauna and Darwin’s own recognition that this fauna and its distribution among the numerous islands triggered a line of thinking that led to his theory of evolution by natural selection.  However, the Galapagos stopover also came toward the end of the voyage, and after maturation of Charles’s conviction of the correctness of Charles Lyell’s worldview in which change is gradual and relentless over long periods of time, allowing highly improbable events to become commonplace, like the lifting up of the ocean floor to become the high Andes.  He had read about the Galapagos and was eager to see these volcanic islands where raw, new land was almost at its moment of birth and certainly in its early infancy.  Here he could see life just getting established.  What he saw was a fauna and flora composed of only a few species, unique to these islands but clearly related to the fauna and flora of South America, filtered by ability to cross 600 miles of ocean. 

 

In short, the creation of species seemed to be derivative from what was already available nearby, rather than de novo.  Though he did not mention it in his Journal of Researches, Charles must have noticed that the land animals of the Galapagos were quite different from those of the Cape Verde Islands, which are very similar in being volcanic, arising from beneath the sea, about 600 miles from the nearest continent (Africa), and quite arid though tropical.  The fauna of each archipelago is closely related to that of the nearby continent and very different from the other archipelago, a third of the way around the world.  One would think direct divine creation would be free to generate on both archipelagos the same, or very similar, species well adapted to tropical, arid, oceanic island environments. 

 

Charles admitted in his Journal of Researches that he was slow to realize how much variation existed between closely related species on different islands of the Galapagos archipelago – “it never occurred to me, that the productions of islands only a few miles apart, and placed under the same physical conditions, would be dissimilar.”  He was alerted by a claim by the vice-governor of the islands that he could ascertain the island of origin of each of the famous tortoises just by the shape of the shell.  Charles himself could distinguish three species of mockingbird.  He found mockingbirds on some islands but not on other similar islands, and each of the islands with mockingbirds had only one species.  This was a pattern of distribution consistent with a mockingbird species arriving by chance from South America and landing on one island, from which subsequent generations managed to reach a few other islands and then changed over time in isolation on those other islands.  Charles did not state this conclusion explicitly in his Journal, because he was barely aware of the pattern when he was in the Galapagos.  He missed the pattern entirely among the thirteen species of finches, because he “did not attempt to make a series of specimens from the separate islands.”  He was not even aware that the variation among the finches was enough to constitute separate species until he returned to England and had his collection analyzed by John Gould.

 

When the Beagle departed the Galapagos Islands, Charles had in hand and in mind the important pieces of the “species problem” that challenged the notion of direct divine creation of species that remain unchanged thereafter.  Certainly he and FitzRoy debated this problem as they puzzled over the evidence in the tiny captain’s cabin, making Charles very aware of how controversial it would be to follow his line of thinking about “mutability” of species to its logical conclusions.  However much his thinking had been set in motion, Charles did not admit in his Journal of Researches to evolutionary conclusions during the voyage itself.

 

The Thin Skin of Civilization — the Fuegian Experiment

 

This account of Charles’s observations about species and change during the voyage of the Beagle would be incomplete without mention of his observations about the people he encountered.  Most important were the three Fuegians, a mature man and two adolescents, a boy and a girl, whom FitzRoy had taken back to England from his first voyage to Tierra del Fuego.  He had them schooled to take on the manners of civilization, dressing, talking and acting like proper gentle folk, sufficient to present the threesome at the Court of St. James, in fact, to the Queen herself.  At his personal expense, FitzRoy implemented a grand but naive experiment to return the three Fuegians with an English missionary to establish a foothold for Christianity at the southern extreme of the inhabited world, among a people easily considered among the most primitive in existence.  The crew of the Beagle, Charles included, became quite fond of the two adolescents, charmingly named Jemmy Button and Fuegia Basket.  Certainly all had high hopes when the Beagle put the Fuegians and the missionary ashore to establish an outpost of English civilization among the primitives.  The Beagle then sailed away for a few weeks of coastal surveying and returned to find a disaster. 

 

The “civilized” Fuegians had been quickly co-opted by the local primitives and reabsorbed into the local culture, such as it was.  The missionary himself was besieged and felt at risk to his life.  The Beagle rescued the missionary and sailed away again.  After about a year, the Beagle returned and found only Jemmy Button, who lived like a typical Fuegian savage.  He and his new wife came out to the ship in a Fuegian canoe and spent time with the crew, clearly retaining his ability to interact like an Englishman, with wistful affection for his former comrades.  However, Jemmy freely chose to remain with his primitive wife and his savage life.  For Charles, this deeply troubling experience must have been a profound lesson on the “mutability” of the human person and species, making the boundary separating the gentleman from the savage seem shockingly thin and porous.  And given the animal-like existence of the Fuegians, even the separation of the human from other animals must have seemed distressingly slight.  The very notion of the human being as a special creation in the image of God was challenged.

 

Tahiti and New Zealand — Darwin and FitzRoy on the Missionaries

 

Don’t assume from this incident that Charles’s confidence in the superiority of Christian civilization was shaken.  Our modern mentality might jump to a conclusion of cultural relativism, in which all cultures are of comparable value in their appropriate contexts.  But this was not the mentality of early 19th century England, which was filled with unashamed confidence in the superiority of its own culture.  We “moderns” would deride this mentality as arrogant, paternalistic and imperialistic; however, before settling on this condemnation, we should read with an open mind Charles’s account of the expedition’s stopover in Tahiti.  He was very taken with beauty of the island and its people and of their way of life, including their rather sophisticated culture.  He was equally impressed by the impact of the English missionaries on the culture.  He makes a convincing case that introduction of Christianity by these missionaries actually changed the Tahitian mindset and way of life and thereby provided very real benefits for the average Tahitian, especially by eliminating truly savage practices which had been current only a few years before.

 

In contrast, Charles found the native culture of New Zealand repugnant, despite the same Polynesian roots as Tahiti.  Even worse, in his view, were the newly arrived English colonists.  Thus, Charles was not simply tilting toward his own kind; rather, he was holding all to a higher standard of behavior and civilization, a Christian standard.  This he made clear in his account of his visit to Waimate, a missionary-led agricultural community, where he found young Maoris quite transformed for the better by their adoption of the Christian standard.  Charles and FitzRoy were of one mind on this topic.  In fact, the two friends published a joint article (the first publication for both of them) on the success of the missionaries at Tahiti and at Waimate, New Zealand.  The editors of the Penguin Books edition of the Journal of Researches, Janet Browne and Michael Neve, make an important observation (page 25) that “it seems very probable that  Darwin’s views were shaped as much by his close relationship with FitzRoy as they were by his enthusiasm for Lyell or his own private love-affair with nature.” Charles’s correspondence from the Beagle “indicates a frank, cheerful trust in each other animated by a marked community of tastes and boyish camaraderie” which were fostered by “… long discussions, dangerous journeys, dust, dirt and shared enthusiasms …”

 

Australia — “one Hand has surely worked throughout the Universe” 

 

Finally, I’ll mention Charles’s impressions of Australia, founded as a British colony only 48 years before the Beagle’s visit in early 1836.  He was duly impressed by the uniqueness of the Australian fauna, especially the dominance of marsupial mammals.  But he argued from his observation of an ant-lion capturing insects in its unique conical pitfall trap, just as its sister species would in Europe, to reject the notion this mostly different fauna might be proof that two Creators were at work, one in Australia, the other elsewhere – “one Hand has surely worked throughout the Universe.” 

 

Charles noted the remarkable development of the economy and culture of British Australia.  Returning from his first walk around Sydney, Charles was “full of admiration at the whole scene.  It is a most magnificent testimony to the power of the British nation.  Here, in a less promising country, scores of years have effected many times more, than the same number of centuries have done in South America.  My first feeling was to congratulate myself that I was born an Englishman.” 

 

As he came to know Australia better, however, Charles was disappointed in the state of society, its focus on acquiring wealth, its treatment of the aborigines and the convict servants, and its low interest in intellectual pursuits.  He decided he could never willingly follow the many other Englishmen emigrating to Australia.  His parting comment was “Farewell, Australia! you are a rising infant and doubtless someday will reign a great princess in the south: but you are too great and ambitious for affection, yet not great enough for respect.  I leave your shores without sorrow or regret.”  Rather harsh words!  Which Australia must have forgiven or forgotten as the new nation named the capital city and major port of its Northern Territory after Charles Darwin!

 

Charles on the Question of God — Answers from Nature, Society and Family Life

 

This post brings to conclusion my series of four posts reviewing Charles Darwin’s voyage of discovery with Captain Robert FitzRoy and the Beagle.  This was the most formative and influential event of Charles’s life.  Almost all that followed in his scientific and writing career built upon the relationships, events and observations I’ve tried to summarize for you.  What I will do from this point onward is review the post-voyage unfolding of Charles’s thinking and activities leading to his theory of evolution and his gradual abandonment of belief in the God of early 19th century English Christianity.  I will explore the possibility that the theory and the abandonment of belief were not necessarily cause and effect, as we all have come to assume.  My exploration will go as deeply as it can into Charles Darwin’s personality and family life and into the nature and origin of his society’s thinking about God.  My hypothesis is that these personal and social factors influenced Charles’s attitude toward God and religion at least as much as his observations of nature and Man and the theory he concocted to explain it all. 

 

 

Copyright 2008 by Chris Dunford.  May be quoted in part or in full only with attribution to Chris Dunford (www.darwinwatch.wordpress.com)

 

 

 

 

The Voyage of the Beagle – Focus on Geology

I long associated Charles Darwin’s round-the-world voyage solely with biology and evolution of living creatures, but that focus came after his return to England.  Certainly, Charles spent a large portion of the five years observing, collecting, classifying, experimenting with, and speculating about the animals and plants he found.  This activity tapped his life-long passion for observing and collecting from the natural world.  As he matured into a would-be naturalist under the guidance of Professor Henslow and others, Charles turned passion into profession.  As a naturalist, however, Charles was also interested in the inanimate components of nature, especially the fascinating variety of rocks and landscapes and climates.  It was typical of naturalists of his time to be interested in everything, looking at the whole even as they collected and described its parts.  The more sophisticated naturalists were natural historians and philosophers, speculating continually on the who, what, when, where, how and why of the natural scenes their educated curiosity drove them to investigate.

  

Putting Lyell to the Test in South America

 

Just in the few months before the voyage of the Beagle, Charles was introduced to the emerging science of geology by Professor Adam Sedgwick of Cambridge University.   In the three centuries before the 1830s, natural philosophy had advanced toward what we think of as scientific method and evidence-based theory, first in astronomy and physics, then chemistry.  Charles did not feel capable of mastering the mathematics needed to fully participate in these scientific specialties, but he appreciated their power to explain the material world in material terms – focusing on proximate causes that a person can directly or vicariously appreciate with the body’s senses, rather than on ultimate causes beyond human comprehension.  Charles joined his older brother, Erasmus, in doing chemical experiments in a shed near his house, often generating obnoxious fumes that earned Charles the nickname “Gas” among his schoolmates.  He learned what it means to experiment and to predict the outcome from prior experience and to be open to the possibility of surprises that force revision of future predictions.  Charles also saw how much sophisticated scientists and their useful knowledge were admired by well-educated men and women of social standing.  Esteem could be achieved by a career in such science, and geology was just then transforming into such science, and Sedgwick made the practice of this science accessible to Charles. 

 

Armed with the first volume of Charles Lyell’s Principles of Geology, Charles realized during the first landing of the voyage, in the Cape Verde Islands, his opportunity to become an esteemed contributor to the emergence of scientific geology.  The distinctly different layers of rock, lying one upon another, presumably in the same sequence in which each was deposited, told a geological history of the island of São Tiago. 

 

Mainstream thinking of the time, conforming to the Biblical story, maintained that the land was stable in the forms originally created and only the level of the sea had risen and fallen over time; the time periods allowed for inundation were relatively short and few.  Lyell (building on the work and words of others, of course) proposed that the land itself had been transformed over time by the same geological processes experienced in the present age – erosion and deposition, volcanic eruptions, and earthquakes.  Moreover, whole blocks of land the size of islands and countries and even continents could rise and fall relative to each other and the level of the oceans.  Lyell proposed cycles of erosion of rocks of varying chemical composition, deposition by water and wind of the eroded rock and organic material in lakes and shallow seas, transformation of these deposits into new types of rock under the weight of overlaying deposits and water, perhaps followed by volcanic activity that spread layers of lava from deep in the earth over the earlier deposited layers, then all uplifted in a series of small events accompanied by earthquakes, until all that had been submerged in the sea now stands inches or feet or even miles above the current sea level.  Acknowledging that all this complex process must require substantial intervals of time, Lyell proposed that the earth was millions, not thousands of years old. 

 

Lyell’s proposed principles were like a dictionary enabling Charles to read the story of the rocks and the layers of São Tiago.  The story fit the facts in front of him together so well that he was “convinced of the infinite superiority of Lyell’s views over those advocated in any other work known to me” (from his Recollections).  This particularly excited Charles, because neither Lyell nor other British geologists had visited South America, giving ambitious Charles the opportunity to be the first to apply the principles to the landscapes he would soon see first hand.  He could test the explanatory power of Lyell’s principles– perhaps even refine and add to this grand theory of the earth. 

 

The Coasts of the Southern Cone — a Continent on the Move Upward

 

After four months on the coast of Brazil, based at Bahia and Rio de Janeiro, the Beagle expedition spent nearly two years (July 1832 to May 1834) working up and down the coast of Argentina, from Uruguay to Tierra del Fuego, with a couple of visits to the Falkland Islands.  Charles left the Beagle several times to make long-distance excursions inland.  All along the shore of the essentially unbroken Argentine and Patagonian plains, he found thick deposits of alluvium (shingle, gravel and mud) that looked very much like they had been carried by rivers and laid to rest in smooth layers underwater in the estuaries where these rivers met the South Atlantic.  Yet these smooth layers of alluvium now stood a few feet to several hundred feet above sea level.  Were they gradually uplifted from the sea, as Lyell would suggest, or had the sea suddenly risen at some point to flood these plains and then withdrawn?  The smoothness of the plains and the sea mollusk shells embedded fairly evenly and deeply in the alluvium gave evidence of gradual uplift from under the sea.  Charles also found that the marine species represented in these layers were quite similar to the species found living in the present estuaries, which indicated the uplift had been fairly recent.  Was it possible that the whole of this long coast was rising up from the sea?  This question made Charles eager to see the mountainous Chilean side of the “southern cone” of South America, hoping for further evidence that the whole of southern South America was rising.

 

From June 1834 to September 1835, the Beagle expedition worked up and down the coast of Chile and Peru.  The southern coast of Chile, from Chiloe Island to Tierra del Fuego, is an archipelago of mountainous islands.  The line of mountains continues northward and inland from the coast north of Chiloe Island, becoming the highest Andes.  When Charles hiked into the coastal hills of central Chile near Valparaiso, he looked out across low mountains and valleys intervening between the coast and the Andes.  The valleys were filled by fog, and the mountains protruded from the sea of fog like the mountain islands of the southern archipelago.  This image gave visual substance to Charles’s hypothesis that the flat valleys had been the bottoms of ancient inlets and deep bays like those farther to the south, later drained as they were uplifted above sea level.  What about the high cordillera of the Andes in the hazy distance? 

 

Evidence in the Andes

 

Charles twice ventured into the Andes from Valparaiso, the second time doing a complete traverse by one alpine pass to the Argentine side, then back to Chile by another pass north of the first.  At 13-14,000 feet elevation, he found fossil shells of marine mollusks! Around 7,000 feet, Charles made an even more remarkable discovery – a standing grove of tree trunks petrified in white silica and calcareous spar, emerging from volcanic sandstone that had once entombed the trunks and then eroded away to reveal them transformed to stone.  Though he had little trouble interpreting this scene, Charles was still astonished by his conclusion.  From his Journal of Researches, “I saw the spot where a cluster of fine trees had once waved their branches on the shores of the Atlantic, when that ocean (now driven back 700 miles) approached the base of the Andes.”  The evidence showed that the land with its upright trees had been “let down to the depths of the ocean,” covered by sediment, and this again by enormous streams of submarine lava, then more sediment followed by more lava, repeated five times.  All this was uplifted so that he “now beheld the bed of that sea forming a chain of mountains more than 7,000 feet in altitude.” “Vast, and scarcely comprehensible as such changes must ever appear, yet they have all occurred within a period recent when compared with the history of the Cordillera; and that Cordillera itself is modern as compared with some other of the fossiliferous strata of South America.”

 

Eruptions and the Earthquake

 

The Andes testify to both the violence and the speed of geological processes, though belied by long periods (in human terms) of apparent calm.  But Charles and the Beagle crew actually experienced the episodic violence that drives mountain building.  Between his two journeys into the Andes, Charles sailed south with the Beagle to survey Chiloe Island and the Chronos Archipelago during the Southern Hemisphere summer (still the weather was rough and tempestuous for weeks).  On the night of January 18, 1835, the volcano Osorno, a hundred miles inland, lit up the sky with a spectacular eruption.  They learned later that the volcanoes Aconcagua, 480 miles to the north, and Coseguina, another 2,700 miles farther north, had erupted on the same night.  Just four weeks later, while Charles and his servant, Sims Covington, were ashore near Valdivia, the area was struck by a massive earthquake.  “It came on suddenly, and lasted two minutes; but the time appeared much longer.  The rocking of the ground was most sensible…There was no difficulty in standing upright, but the motion made me giddy…Captain FitzRoy and the officers were at the town during the shock, and there the scene was more awful; for although the houses, being made from wood, did not fall, yet they were so violently shaken that the boards creaked and rattled.  The people rushed out of doors in the greatest alarm.”  Charles concluded that “the world, the very emblem of all that is solid, has moved beneath our feet like a crust over a fluid; one second of time has conveyed to the mind a strange idea of insecurity, which hours of reflection would never have created.”

 

Two days later the Beagle sailed into the harbor of Concepcion and found the city utterly destroyed by the earthquake.  The epicenter had been just offshore, and a massive tidal wave had swept the shoreline of structures, livestock and people.  Charles devoted several pages of his Journal of Researches to description of the devastation.  While lamenting the loss of life and property, Charles was also deeply interested in what the patterns of destruction told him about the movements of the earth and the ocean during the quake and its after-shocks.  “The most remarkable effect (or perhaps speaking more correctly, cause) of this earthquake was the permanent elevation of the land.”  FitzRoy’s detailed survey work before and after the quake provided “a mass of evidence in proof of such elevation, far more conclusive than that on which geologists on most other occasions placed implicit faith.”  They calculated that, since the previous massive earthquake of 1751, the land had risen four fathoms – 24 feet!  With enough time allowed, Charles had no problem understanding how the Andes had been lifted up.  The earthquake had been accompanied by simultaneous eruptions of a train of volcanoes in the Andes of central Chile.  Charles concluded that the earthquake and volcanic activity formed parts of one great phenomenon underlying an area onshore and offshore that measures 700 by 400 miles.  In line with Lyell’s theory, all the evidence pointed Charles toward the conclusion “that a vast lake of melted matter, of an area nearly doubling in extent that of the Black Sea, is spread out beneath a mere crust of solid land.”

 

Volcanic Islands and Coral Atolls — Rising from the Ocean and Under the Waves Again 

 

Later in 1835, the Beagle expedition left the coast of South America at last and set sail for home – westward across the vast Pacific Ocean.  The Galapagos Islands were the first stop en route.  The expedition spent a bit over one month surveying the islands; Charles and Covington and some others of the crew were put ashore for a few days on several of the many islands.  Charles knew beforehand that the islands were of recent volcanic origin, evidenced by the activity of volcanoes and the vast expanses of recent lava flows.  He could see for himself that the volcanically very active western islands are younger than the eastern islands, which are lower, more eroded, more vegetated, and showing no present-day volcanic activity.  He correctly concluded that these islands had all originated as subterranean volcanoes that built upward until they broke the ocean surface.  In addition to uplift from beneath the ocean, Charles also had opportunity to see evidence of subsidence – volcanic craters partially submerged to form crescent bays, like what is now named Darwin Bay on Tower Island (Isla Genovesa).  These observations no doubt encouraged Charles in his budding hypothesis about the origin of coral atolls, though he had only read about them up to this point.  The Galapagos waters are too cold for corals (despite being right on the Equator), but Charles saw many of these thin circles of low-lying land as the Beagle moved on through the Tuamotu (or Dangerous) Archipelago to Tahiti.

 

After stops in New Zealand and Australia, the Beagle made a detour to survey the Keeling or Cocos Islands, in the Indian Ocean southwest of Java in Indonesia.   The main island is a lagoon atoll of coral formation similar to the Tuamotu atolls.  The deep soundings of the survey work on the ocean side of the lagoon island verified that live corals could not be found at depths in excess of 120 feet (coral polyps depend on sunlight penetrating the water), and at greater depths, they found only calcareous rock or sediment formed from dead coral, the same material of which the atoll’s islets were composed.

 

Charles’s theory was that all coral reefs start as fringes of the tropical shore of rocky land.  If the land rises, the exposed coral dies, but new living reef is formed along the new shore to the depth of 120 feet.  If the land subsides, it sinks into the water slowly enough to allow the tiny coral polyps to build their reef upward to remain just below the ocean surface.  As the gently sloping shore sinks into the water, however, the coral polyps, being most active on the side toward the open ocean waves, build vertically toward the sun on the calcareous base created by their sunken predecessors; thus, the rocky shore gradually withdraws from the reef in contact with the open ocean, leaving a shallow lagoon in between.  In the case of large islands, like New Caledonia, or even continents, like Australia, these became great barrier reefs.  In the case of isolated oceanic islands, which rise as submarine volcanoes from the seafloor and then subside back under the ocean surface, these become coral atolls.  The reef first forms a fringe around the rising volcano; the subsiding volcano then leaves a lagoon encircling the sinking volcanic peaks still above water (like spectacular Bora Bora).  Then even those remaining peaks sink below the lagoon surface, leaving only the outer reef and a thin circle of calcareous materials piled up by the ocean’s pulverizing waves into islets just behind the outer reef, barely high enough to be visible from a distance – an atoll in the middle of the open ocean.

 

His theory was a masterpiece of deductive reasoning.  From Charles’s Recollections, “No other work of mine was begun in so deductive a spirit as this, for the whole theory was thought out on the west coast of South America, before I had seen a true coral reef.”  This theory, which captured the admiring attention of Charles Lyell himself upon Charles Darwin’s return to England, overturned all others and still stands today.  Charles was rightly pleased with his theory – how he derived the ideas from his geological observations in South America and how they were verified by the evidence of coral reefs around the world.  In his Journal of Researches, Charles built on the theory of reef formation to show that the distribution of the three types of coral reef – fringing the shore, encircling islands with lagoons, and forming barrier reefs and atolls – indicates that large blocks or plates of the earth’s surface (including seafloor) are tilting, so that one end is rising while the other is subsiding.  Charles thereby extended his theory of reef formation, built on his personal verification of Lyell’s principles, to even more dramatically demonstrate “the never-ceasing mutability of the crust of this our World.”

 

The next and last post on the voyage of the Beagle reviews the major biological and anthropological observations of Charles Darwin during 1831 to 1836.

 

Copyright 2008 by Chris Dunford.  May be quoted in part or in full only with attribution to Chris Dunford (www.darwinwatch.wordpress.com)

 

 

 

 

 

 

 

 

 

 

 

 


Welcome to DarwinWatch

This blog by Chris Dunford explores the meaning of Charles Darwin's life, work and words in relation to the Science-Religion Debate. It is committed to intellectual honesty and historical perspective. Please click on the "Why this Blog" tab under the banner photo to learn more. Started in July 2008, this has been a very slow work-in-progress. Be patient with me and check in occasionally, if only to enjoy the banner photo!