Introduction to Coral reefs

Coral reefs (1842) was Darwin’s first monograph. It addressed an immensely ambitious subject. It is perhaps second only to the Origin for its masterful deduction from observation, leading to the construction of a theory that if proved would exceed all previous attempts and virtually solve its subject. The power of Darwin’s monograph was well recognised by his contemporaries as a major scientific work. It was for this book and his monographs on barnacles that Darwin was awarded the Copley Medal by The Royal Society in 1864.

This introduction is not intended to repeat the bibliographical history of Coral reefs which, as with all Darwin’s books, was dealt with extensively by R. B. Freeman. Coral reefs was first published in May 1842. Darwin brought out a revised second edition in 1872 and a third edition, with a substantial appendix by T. G. Bonney, appeared in 1889. The first edition was enthusiastically reviewed by Jackson 1842.

By 1838, at the age of twenty-nine, Darwin had sent his Journal of researches to the printers and organised the publication of his Zoology of the Beagle, Darwin wanted to proceed with his planned Geology of the voyage of the Beagle, a project he had conceived some seven years previously, in April 1832. By 1838 he saw himself as an geologist who had carved out a large part of the world as ‘his’ scientific territory, but he also saw the need to prove himself by publishing his observations and theories, much in the way that few scientists will be taken seriously today until they have published their doctoral theses. By the time he sat down to write the first page of what became Coral reefs he envisaged two books, the first on reefs and oceanic islands, the second on the continent of South America. It did not take him long to realise that reefs would require a book of their own.

Darwin had already drafted his coral theory before leaving the Pacific in November 1835. He believed they formed in a gradual series from fringing reefs (such as those of Mauritius), through barrier reefs to atolls (such as Keeling) . The maturation of his brilliant explanation for the formation of atolls is explained in the introductions to his Santiago and Despoblado field notebooks.

Coral reefs were a subject of lively scientific debate in the 1830s and were in fact one of the key scientific objectives of the Beagle’s orders from the Admiralty (see Narrative 2: 38). Lyell devoted a large section of the second (1832) volume of his Principles of geology to this very subject, and his explanation for atolls was that they were coral reefs growing up from the crater rims of sunken volcanoes. As Lyell’s strongest disciple, Darwin had to face the fact that he disagreed completely with the older man on this issue, but in the event Lyell jumped up and down for joy when Darwin explained to him his radically different theory.

In essence Darwin’s theory was as follows: in clean, agitated, tropical seas corals will form fringing reefs just below low tide level. If the coastline is being elevated (as for example may happen if the island is an active volcano) this type of reef should persist but as soon as the living coral is raised above the surf it will die and become a strip of white limestone. If the coastline is stable, the coral will gradually grow out from the shore to become a barrier reef. If the coast is sinking, as Darwin thought was happening to hundreds of islands in the south Pacific, the coral might keep pace by growing upwards but as the land sinks beneath the waves all that would remain would be a more or less circular atoll. Eventually the rate of subsidence might prove too fast, or (perhaps as in our own times of global warming) sea level will rise too fast and the atoll will die:

Fringing-reefs are thus converted in to barrier-reefs; and barrier-reefs, when encircling islands, are thus converted into atolls, the instant the last pinnacle of land sinks beneath the surface of the ocean (p. 147).

All of this is the result of the accumulation of the calcareous skeletons of untold billions of simple organisms. To paraphrase Darwin’s devastating footnote on p. 94, none of these little creatures has the slightest idea what it is achieving, it just happens. Darwin’s theory was generally, but not universally, accepted in his lifetime. Although it was not until deep borings on Bikini atoll proved the theory correct in the 1950s. It is true that Darwin underestimated the changes of sea level caused by Ice Ages and even today we do not fully understand all the factors involved. By the 1970s, however, the theory of plate tectonics had more or less provided an explanation for the gradual subsidence of vast areas of the ocean floor as it moves away from the mid-ocean ridges and for most of the other large-scale phenomena described by Darwin in Coral reefs.

In Coral reefs Darwin ‘reads’ his evolutionary sequence ‘backwards’, in three chapters starting with his own first-hand descriptions of Keeling Atoll, then barrier reefs, then fringing reefs. These three chapters are followed by three more of analysis, the fourth chapter showing that the distribution of the three types is far from random and in fact begs a large-scale explanation. The fifth chapter presents Darwin’s theory, summarised on p. 98, and deals with objections, while the sixth chapter sees how the theory explains the data of present and fossil reefs and ends with a recapitulation, the prototype for the one in the Origin.

Coral reefs has been undervalued for the tightness of its logical structure and for the sheer boldness of its argument. It could also be argued that it is one of the finest scientific books ever published in which illustrations (in this case numerous detailed charts and one enormous world map showing all known reefs) are used as an integral part of that argument. Darwin was no Rembrandt, but he certainly understood that his charts spoke ‘more plainly to the eye, than any description could do to the ear’ (p. 103).

The Origin of 1859 has a similar structure, starting with the minutiae of artificial selection, leading into a long argument for the theory of natural selection, followed by a demonstration of how the theory will explain the vast panoply of life past and present. Coral reefs differs from the Origin, however, by including a large appendix in which Darwin presented an exhaustive survey of coral reefs of the world. Of course it was Darwin’s intention to publish a ‘big book’ on natural selection to include his vast compendium of substantiating materials, but he postponed that plan when Wallace came up with such a similar theory before Darwin had published his own version. The Origin, unlike Coral reefs, has no footnotes or references. Only the first two chapters of the ‘big book’ on natural selection were published in Darwin’s lifetime, as Variation under domestication (1868).

It was Darwin’s genius to see that coral reefs, although plainly geological structures on a stupendous scale, were created by slow, gradual growth of countless billions of tiny creatures over vast periods of time. This was Lyell’s ‘uniformitarian’ principle writ large and in perfect symmetry to Darwin’s last book on Earthworms, in which in the year before his death he showed how the humble worm toiling literally beneath our feet was creating the landscape. In Coral reefs and Earthworms Darwin was exalting tiny animals which, given time, were changing the face of the Earth. This was at the core of his life’s work, as encapsulated in the Origin, in which he created a view of nature in which all life is evolving along particular pathways but with no divine plan.

One could argue that Coral reefs was the first volume of Darwin’s philosophy of nature, a treatise of truly Victorian proportions to rival the longest novels of his time, and which took him all his life to publish and which he never explicitly titled. Coral reefs was the first volume in the treatise which demonstrated how slow gradual change, given enough time, could account for the entire history of life. Coral reefs also – by presenting the types of reef as an evolutionary series – demonstrated a methodology for interpreting patterns only observable at the present as the results of history. Thus on p. 39 in describing the Maldives Darwin reflects how: 'A perfect series, such as we have here traced, impresses the mind with an idea of actual change.'

Through a whole series of other volumes, from Different forms of flowers through Orchids and culminating in the Origin, Darwin was giving to the historical sciences a methodology as rigorous as any in Newton’s ahistorical physical sciences. But not content with raising forever the status of the historical sciences, Darwin also gave them, by offering the first testable theory of evolution, a research programme of practical science for the next thousand years.

Perhaps even more significant for us all in the long run, Darwin went even beyond these colossal achievements and deeply shook the Western belief in a purposeful universe. Darwin’s life’s work may be interpreted as one long and cruelly successful assault on William Paley, whose rooms in Cambridge Darwin is said to have inherited and whose Natural Theology had so charmed him while a student. Paley taught that God’s goodness is plainly seen in the exquisite adaptation that we see everywhere in nature. Darwin turned this upside-down and inside-out by showing that these adaptations were the result of a pitiless and utterly amoral struggle for survival in which God played no part whatsoever. As he wrote in Coral reefs in a remarkably Malthusian passage

In an old-standing reef, the corals, which are so different in kind on different parts of it, are probably all adapted to the stations they occupy, and hold their places, like other organic beings, by a struggle one with another, and with external nature; hence we may infer that their growth would generally be slow, except under peculiarly favourable circumstances (p. 76).

In short, Coral reefs should be far more widely read, not just because it is one of the most elegantly written and constructed books written by one of greatest thinkers in history, but because it was the first brick laid on the foundations of a revolutionary view of life. It is not just a book about reefs, it is a book which sweeps across the ecology and geology of the whole world.

Gordon Chancellor

July 2008

Darwin, C. R. 1842. The structure and distribution of coral reefs. Being the first part of the geology of the voyage of the Beagle, under the command of Capt. Fitzroy, R.N. during the years 1832 to 1836. London: Smith Elder and Co. Text Image PDF F271

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