CHAPTER IV.

CAMBRIDGE--LONDON--WORK UPON THE COLLECTIONS--MARRIAGE--GEOLOGICAL WORK--JOURNAL OF THE VOYAGE--CORAL REEFS--FIRST RECORDED THOUGHTS ON EVOLUTION (1837–42).

Darwin reached England October 2nd, 1836, and was home at Shrewsbury October 5th (according to his Letters; the 4th is the date given by Francis Darwin in the “Life and Letters”). The two years and three months which followed he describes as the most active ones he ever spent. After visiting his family, he stayed three months in Cambridge, working at his collection of rocks, writing his “Naturalist’s Voyage,” and one or two scientific papers. He then (March 7th, 1837) took lodgings in 36, Great Marlborough Street, London, where he remained until his marriage, January 29th, 1839. The apathy of scientific men--even those in charge of museums--caused him much depression, and he found great difficulty in getting specialists to work out his collections, although the botanists seem to have been keener than the zoologists.

The commencement of his London residence is of the deepest interest, as the time at which he began to reflect seriously on the origin of species. Thus he says in the “Autobiography”:--“In July I opened my first note-book for facts in relation to the Origin of Species, about which I had long reflected, and never ceased working for the next twenty years.” Furthermore, his pocket-book for 1837 contained the words:--“In July opened first note-book on Transmutation of Species. Had been greatly struck from about the month of previous March” (he was then just over twenty-eight years old) “on character of South American fossils, and species on Galapagos Archipelago. These facts (especially latter) origin of all my views.” It is, perhaps, worth while to explain in greater detail the nature of this evidence which appealed so strongly to Darwin’s mind. The Edentata (sloths, ant-eaters, armadilloes, etc.) have their metropolis in South America, and in the later geological formations of this country the skeletons of gigantic extinct animals of the same order (Megatherium, Mylodon, Glyptodon, etc.) are found; and Darwin was doubtless all the more impressed by discovering such remains for himself. In his “Autobiography” he says: “During the voyage of the _Beagle_ I had been deeply impressed by discovering in the Pampean formation great fossil animals covered with armour like that on existing armadilloes;...”

Darwin was thus led to conclude that there was some genetic connection between the animals which have succeeded each other in the same district; for in a theory of destructive cataclysms, followed by re-creations--or, indeed, in any theory of special creation--there seemed no adequate reason why the successive forms should belong to the same order. In his “Naturalist’s Voyage Round the World” he says, speaking of this subject: “This wonderful relationship in the same continent between the dead and the living will, I do not doubt, hereafter throw more light on the appearance of organic beings on our earth, and their disappearance from it, than any other class of facts” (p. 173 in the third edition).

[Sidenote: THE GALAPAGOS.]

The other class of evidence which impressed him even more strongly was afforded by the relations between the animals and plants of the several islands of the Galapagos Archipelago and between those of the Archipelago and of South America, nearly 600 miles to the East. Although the inhabitants of the separate islands show an astonishing amount of peculiarity, the species are nearly related, and also exhibit American affinities. Concerning this, Darwin writes in his “Voyage” (p. 398 in the third edition): “Reviewing the facts here given, one is astonished at the amount of creative force--if such an expression may be used--displayed on these small, barren, and rocky islands; and still more so at its diverse and yet analogous action on points so near each other.” Here, too, the facts were unintelligible on a theory of separate creation of species, but were at once explained if we suppose that the inhabitants were the modified descendants of species which had migrated from South America--the migrations to the Archipelago and between the separate islands being rendered extremely rare from the depth of the sea, the direction of the currents, and the absence of gales. In this way time for specific modification was provided before the partially modified form could interbreed with the parent species and thus lose its own newly-acquired characteristics.

Although Darwin made these observations on the _Beagle_, they required, as Huxley has suggested (Obituary [1888], “Darwiniana”: Collected Essays, vol. ii., pp. 274–275. London, 1893), careful and systematic working out before they could be trusted as a basis on which to speculate; and this could not be done until the return home. The following letter written by Darwin to Dr. Otto Zacharias in 1877 confirms this opinion. It was sent to Huxley by Francis Darwin, and is printed in “Darwiniana” (_l. c._, p. 275):--

“When I was on board the ‘Beagle,’ I believed in the permanence of species, but, as far as I can remember, vague doubts occasionally flitted across my mind. On my return home in the autumn of 1836, I immediately began to prepare my journal for publication, and then saw how many facts indicated the common descent of species, so that in July, 1837, I opened a note-book to record any facts which might bear on the question. But I did not become convinced that species were mutable until I think two or three years had elapsed.”

It is interesting to note that both the lines of evidence which appealed to Darwin so strongly, point to evolution, but not to any causes of evolution. The majority of mankind were only convinced of this process when some conception as to its causes had been offered to them; Darwin took the more logical course of first requiring evidence that the process takes place, and then inquiring for its causes.

[Sidenote: EARLY NOTES ON SPECIES.]

The first indication of these thoughts in any of his published letters is in one to his cousin Fox written in June, 1838, in which, after alluding to some questions he had previously asked about the crossing of animals, he says, “It is my prime hobby, and I really think some day I shall be able to do something in that most intricate subject--species and varieties.”

He is rather more definite in a letter to Sir Charles Lyell, written September 13th in the same year:--

“I have lately been sadly tempted to be idle--that is, as far as pure geology is concerned--by the delightful number of new views which have been coming in thickly and steadily,--on the classification and affinities and instincts of animals--bearing on the question of species. Note-book after note-book has been filled with facts which begin to group themselves _clearly_ under sub-laws.”

On February 16th, 1838, he was appointed Secretary of the Geological Society, a position which he retained until February 1st, 1841. During these two years after the voyage he saw much of Sir Charles Lyell, whose teachings had been of the greatest help to him during the voyage, and whose method of appealing to natural causes rather than supernatural cataclysms undoubtedly had a most important influence on the development of Darwin’s mind. This influence he delighted to acknowledge, dedicating to Lyell the second edition of his “Voyage,” “as an acknowledgment that the chief part of whatever scientific merit this ‘Journal’ and the other works of the author may possess has been derived from studying the well-known and admirable ‘Principles of Geology.’”

[Sidenote: EARLY WORKS.]

At this period he finished his “Journal,” which was published in 1839 as Vol. III. of the “Narrative of the Surveying Voyages of Her Majesty’s Ships _Adventure_ and _Beagle_.” A second edition was published in a separate form in 1845 as the “Journal of Researches into the Natural History and Geology of the Countries visited during the Voyage of H.M.S. _Beagle_ round the World, under the command of Captain Fitz-Roy, R.N.”; and a third edition--but very slightly altered--in 1860, under the title “A Naturalist’s Voyage: Journal of Researches, etc.” This book is generally admitted to deserve above all others the generous description which Darwin gave to Sir Joseph Hooker of Belt’s admirable “Naturalist in Nicaragua”--as “the best of all Natural History journals which have ever been published.”

A comparison between the first and second editions indicates, but by no means expresses, his growing convictions on evolution and natural selection. Natural selection he had not discovered when the MS. of the first edition was complete; and if we had no further evidence we could not, from any passage in the work, maintain that he was convinced of evolution. His great caution in dealing with so tremendous a problem explains why the second edition does not reflect the state of his mind at the time of its publication. He tells us (“Autobiography”) that in the preparation of this second edition he “took much pains,” and we may feel confident that much of this care was given to the decision as to how much he should reveal and how much withhold of the thoughts which were occupying his mind, and the conclusions to which he had at that time arrived. That he did attribute much importance to the evolutionary passages added in the second edition is shown by his letter to Lyell (July, 1845), in which he alludes to some of them, and specially asks Lyell to read the pages on the causes of extinction.

He also edited and superintended the “Zoology of the Voyage of H.M.S. _Beagle_,” the special parts of which were written by various eminent systematists, and appeared separately between 1839 and 1843.

He also read several papers before the Geological Society, including two (1838 and 1840) on the Formation of Mould by the Action of Earth-Worms--a subject to which he returned, and upon which his last volume (published in 1881) was written. He also read a paper on the Parallel Roads of Glen Roy before the Royal Society (published in the _Phil. Trans._, 1839). These wonderful parallel terraces are now admitted to be due to the changes of level in a lake following those of an ice-barrier at the mouth of the valley. At the time Darwin studied them, the terraces were believed to have been formed by a lake dammed back by a barrier of rock and alluvium; this he proved to be wrong, and as no other barrier was then available--for the evidences of glaciation had not then been discovered by Agassiz--he was driven, on the method of exclusion, to the action of the sea. Upon this subject he says, in the “Autobiography,” “My error has been a good lesson to me never to trust in science to the principle of exclusion.”

On January 29th, 1839, he married his cousin, Emma Wedgwood, the daughter of Josiah Wedgwood, of Maer. They resided at 12, Upper Gower Street until September 14th, 1842, when they settled at Down.

The few graceful and touching words in which Francis Darwin, in the “Life and Letters,” alludes to his father’s married life show how deep is the debt of gratitude which the world owes to Mrs. Darwin; for without her constant and loving care it would have been impossible for Darwin to have accomplished his life-work.

[Sidenote: ON CORAL REEFS.]

During these years in London his health broke down many times; so that he says, in the “Autobiography”: “I did less scientific work, though I worked as hard as I possibly could, than during any other equal length of time in my life.” He chiefly worked at his book on “The Structure and Distribution of Coral Reefs,” published in 1842 (second edition in 1874). This work contains an account of Darwin’s well-known theory upon the origin of the various coral formations--fringing reefs, barrier reefs, and atolls--by the upward growth of the reef keeping pace with the gradual sinking of the island upon which it is based, so that the living corals always remain at the surface under the most favourable conditions, while beneath them is an ever-thickening reef formed of dead coral, until at length, by continuing this process, the climax is reached in the atoll, in which the original island has altogether disappeared beneath the surface of a central lagoon enclosed in a ring formed by the living edge of the reef. This theory, after being accepted for many years, has recently been disputed, chiefly as the result of the observations made on the _Challenger_ expedition. It is contended by Dr. John Murray “that it is not necessary to call in subsidence to explain any of the characteristic features of barrier reefs or atolls, and that all these features would exist alike in areas of slow elevation, of rest, or of slow subsidence” (_Nature_, August 12th, 1880, p. 337). It cannot be said that this controversy is yet settled, or that the supporters of either theory have proved that the other does not hold--at any rate, in certain cases.

Among his geological papers written at this time was one describing the glacial phenomena observed during a tour in North Wales. This paper (_Philosophical Magazine_, 1842, p. 352) is placed by Sir Archibald Geikie “almost at the top of the long list of English contributions to the history of the Ice Age.”

At this time, too, he was reflecting and collecting evidence for the great work of his life. Thus in January, 1841, he writes to his cousin, Darwin Fox, asking for “all kinds of facts about ‘Varieties and Species.’”