charles darwin’s beagle voyage, fossil vertebrate ... - darwin... · which they diﬀer slightly...

Charles Darwin’s Beagle Voyage, Fossil Vertebrate Succession,

and ‘‘The Gradual Birth & Death of Species’’

PAUL D. BRINKMANNorth Carolina Museum of Natural Sciences11 W. Jones Street

Raleigh, NC 27601-1029USAE-mail: [email protected]

Abstract. The prevailing view among historians of science holds that Charles Darwinbecame a convinced transmutationist only in the early spring of 1837, after his Beagle

collections had been examined by expert British naturalists. With respect to the fossilvertebrate evidence, some historians believe that Darwin was incapable of seeing orunderstanding the transmutationist implications of his specimens without the help of

Richard Owen. There is ample evidence, however, that he clearly recognized thesimilarities between several of the fossil vertebrates he collected and some of the extantfauna of South America before he returned to Britain. These comparisons, recorded in

his correspondence, his diary and his notebooks during the voyage, were instances of aphenomenon that he later called the ‘‘law of the succession of types.’’ Moreover, on theBeagle, he was following a geological research agenda outlined in the second volume ofCharles Lyell’s Principles of Geology, which implies that paleontological data alone could

provide an insight into the laws which govern the appearance of new species. SinceDarwin claims inOn the Origin of Species that fossil vertebrate succession was one of thekey lines of evidence that led him to question the fixity of species, it seems certain that he

was seriously contemplating transmutation during the Beagle voyage. If so, historians ofscience need to reconsider both the role of Britain’s expert naturalists and the importanceof the fossil vertebrate evidence in the development of Darwin’s ideas on transmutation.

Keywords: Darwin, transmutation, fossil vertebrate succession, Beagle, agouti,Megatherium, armadillo, nineteenth century

What an immense field for reflection is opened to the mind of thephilosopher, by the survey of the discoveries to which fossil oste-ology has conducted us!

Edward Pidgeon, 18301

1 Pidgeon, 1830, p. 39.

Journal of the History of Biology (2010) 43:363–399 � Springer 2009

DOI 10.1007/s10739-009-9189-9

Introduction

Though it is well known that Charles Darwin made an important col-lection of vertebrate fossils in South America while serving on HMSBeagle,2 relatively little serious attention has been given to the meaningand significance that these specimens held for him during the course ofthe voyage. Among scholars who have written about the role of thefossil vertebrate evidence in the development of Darwin’s thinkingabout the mutability of species there are two competing hypotheses.One early conversion hypothesis holds that he was immediately andprofoundly impressed by the discovery of fossils in South America,which closely resembled the local, extant fauna, and that this – togetherwith other evidence accumulated during the voyage – led him to ques-tion the fixity of species while still on the Beagle. Darwin himself firstadvanced this idea. In at least two publications, he claimed that he firstrecognized the phenomenon of fossil vertebrate succession during thevoyage. The first sentence of On the Origin of Species, for example,reads:

When on board HMS Beagle, as naturalist, I was much struck withcertain facts in the distribution of the inhabitants of SouthAmerica, and in the geological relations of the present to the pastinhabitants of that continent. These facts seemed to throw somelight on the origin of species.3

In an autobiographical sketch written for his family and published byhis son in 1887, Darwin wrote:

During the voyage of the Beagle I had been deeply impressed bydiscovering in the Pampean formation great fossil animals coveredwith armour like that on the existing armadillos; secondly, by themanner in which closely allied animals replace one another inproceeding southwards over the Continent; and thirdly, by theSouth American character of most of the productions of theGalapagos archipelago, and more especially by the manner inwhich they differ slightly on each island of the group; none of theislands appearing to be very ancient in a geological sense. It wasevident that such facts as these, as well as many others, could only

2 See Darwin 1839; Moorehead, 1969; Keynes, 2003; Simpson, 1984, pp. 23–39.3 Darwin, 1859, p. 1.

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be explained on the supposition that species gradually becomemodified; and the subject haunted me.4

This hypothesis was later promoted by his son, Francis Darwin, hisgranddaughter, Nora Barlow, the biologist Cyril D. Darlington, andothers. British Geologist John W. Judd made the strongest case for theimportance of the role of the fossil vertebrate evidence in the earlydevelopment of Darwin’s evolutionary views.5

This view has since fallen into disfavor, however, and a late con-version hypothesis has emerged as the new consensus view among his-torians of science. Some of Darwin’s own remarks would seem tosupport a late conversion. In an 1877 letter to German naturalist OttoZacharias, for example, he wrote:

When I was on board the Beagle, I believed in the permanence ofspecies but, as far as I can remember, vague doubts occasionallyflitted across my mind. On my return home in the autumn of 1836,I immediately began to prepare my journal for publication, andthen saw how many facts indicated the common descent of speciesso that in July 1837, I opened a note-book to record any factswhich might bear on the question. But I did not become convincedthat species were mutable until, I think, two or three years hadelapsed.6

An oft-quoted journal entry from 1837 seems to pin down the verymonth of Darwin’s conversion:

In July opened first note-book on Transmutation of Species. Hadbeen greatly struck from about the month of previous March oncharacter of South American fossils and species on GalapagosArchipelago. These facts origin (especially latter) of all my views.7

4 Darwin, 1959[1887], Vol. I, p. 67. Darwin made a similar claim in a number ofletters, also, including C. Darwin to L. Jenyns, 25 (Nov. 1844), in: Burkhardt and Smith,

1987, p. 84; and, C. Darwin to C. Lyell, (Dec.) 27 (1859), in Burkhardt and Smith, 1991,p. 455.

5 See Darwin, 1909, p. xiii; Barlow, 1946, pp. 166–167; Darlington, 1959, p. 316;

Judd, 1909, pp. 351–353; Judd, 1911. Obviously, early twentieth century scholars didnot enjoy the easy access to Darwin’s manuscript materials that we have today. Con-sequently, their claims about Darwin’s conversion must be taken with a grain of salt.

Francis Darwin and John Judd, on the other hand, had access to Darwin himself. Judd(1909, p. 337, footnote 1) noted that he and Darwin, late in the latter’s life, met peri-odically for ‘‘geology talks.’’

6 Letter, C. Darwin to O. Zacharias, 1877. This quotation appears in numerousplaces, including Darwin, 1893, p. 175.

7 Quoted in de Beer, 1959, p. 1.

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The late conversion hypothesis draws considerable support from theseremarks – especially the latter – which suggest that Darwin did notquestion the fixity of species until after the voyage. But because hecontradicted himself in several places on this question, advocates of alate conversion cannot depend solely on Darwin’s own words. Instead, anumber of scholars have argued that Darwin could not have becomea convinced transmutationist without the aid of London’s expert nat-uralists. With respect to the fossil vertebrate evidence, two principalreasons are most commonly given to show why Darwin could not haveappreciated the evolutionary implications of his fossils during thevoyage. First, Darwin collected fossils for geological rather than zoo-logical purposes, and he made little or no attempt to compare his fossilvertebrate discoveries to the living fauna of South America.8 Second,Darwin was not a competent enough comparative anatomist to noticeor understand the anatomical similarities between the fossil and extantfaunas of South America. This tradition emphasizes Darwin’s insuffi-cient experience as a naturalist, his lack of formal anatomical training,and his dependence on the expertise of the British scientific community.

As early as 1888, Thomas Henry Huxley argued that Darwin’s ideasabout evolution took shape after his return from the voyage:

While at sea, [Darwin] diligently collected, studied, and madecopious notes…. But with no previous training in dissection, hardlyany power of drawing, and next to no knowledge of comparativeanatomy, his occupation with work of this kind – notwithstandingall his zeal and industry – resulted, for the most part, in a vastaccumulation of useless manuscript. …[U]ntil the relations of theexisting with the extinct species … were determined with someexactness, they afforded but an unsafe foundation for speculation. Itwas not possible that this determination should have been effectedbefore the return of the ‘‘Beagle’’ to England.9

Likewise, historian Sandra Herbert singled out the phrase ‘‘if one spe-cies altered’’ in the ‘‘Red Notebook’’ as Darwin’s first substantivespeculation on transmutation to which she assigned a date no earlierthan the end of January, 1837, after the voyage. ‘‘The factual basis for a

8 Gertrude Himmelfarb, who took an extremely dim view of Darwin’s work as anaturalist, argued that his ‘‘geological enterprise was kept quite distinct from the zoo-logical.’’ See Himmelfarb, 1959, pp. 109–110. The quotation appears on p. 109.

9 Huxley, 1896[1888], pp. 271–275. Huxley, who was a champion of the profes-sionalization of British science, was careful not to give too much credit to Darwin, agentleman-naturalist trained for the clergy (although see Desmond, 1997, p. 563 for a

different interpretation).

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transmutationist view’’ appears in Darwin’s Beagle-era notes, Herbertconceded, but judgments of fact on species and varieties required theinput of professional zoologists for verification. Thus, it was only afterhis return to England that Darwin’s speculations on the stability ofspecies could be tied definitively to his observations of nature.10

According to this view, Darwin needed the collaboration of London’sscientific experts, especially the comparative anatomist Richard Owen,who made the requisite study and classification of the fossil vertebrateportion of the Beagle collections, before he could interpret any of hisdata as evidence of transmutation.

Vertebrate paleontologist George Gaylord Simpson, in summarizingthe modern understanding of the phylogenetic relationships of Darwin’sfossil taxa, argued unequivocally that ‘‘Darwin’s collections of fossilmammals could not and did not lead directly to evolutionary conclu-sions. …[N]one of [his] fossils could reasonably be considered asancestral, in an evolutionary sense, to any living species.’’11 Further-more, Michael Ghiselin argued that Darwin’s claim in the first sentenceof Origin (quoted above) is a ‘‘dialectical maneuver’’ intended to stressthe inductive nature of his discovery.12 In other words, readers aremeant to understand that Darwin’s ideas were derived from an accu-mulation of facts found in nature, not mere speculation.

A landmark paper by Frank Sulloway, published in 1982, arguedpersuasively that Darwin became a convert to transmutation in March,1837, after consultations with Owen, John Gould, and others about thenature of his Beagle specimens. Though Sulloway placed most of hisemphasis on the significance of Darwin’s extant Galapagos collections,his argument implied that Darwin’s views on the fossil vertebrate evi-dence remained pre-evolutionary until after the Beagle’s return. In fact,Sulloway made fairly short work of the fossil vertebrate evidence,arguing in a footnote that Darwin’s misidentifications and his failure todistinguish between several different forms confused the evolutionaryimplications of the paleontological evidence.13

10 Herbert, 1974, p. 236; Herbert, 1980.11 Simpson, 1984, p. 36.12 Ghiselin, 1984[1969], pp. 34–35.13 Sulloway, 1982. The footnote appears on p. 353 and directs readers to pp. 88–92 of

Sulloway’s unpublished thesis, ‘‘Charles Darwin and the Voyage of the Beagle (1831–

1836).’’ There Sulloway argued that it would have been ‘‘highly unlikely’’ that Darwincould have derived his ‘‘law of succession’’ from the fossil evidence without expert help.He added that ‘‘it was as a geologist and not as a zoologist that [Darwin] considered his

fossils of value.’’ See Sulloway, 1969, especially p. 92.


In summary, the majority view among historians of science, basedprimarily on the weight of the biogeographical evidence provided by theGalapagos specimens, and following Sulloway, holds that Darwin didnot become a convinced transmutationist until early 1837, after hisreturn from the Beagle voyage. This now orthodox view can be found inmany recent Darwin biographies and histories of biology.14 A biogra-phy by Adrian Desmond and James Moore, for example, describes thecrucial roles played by Owen and geologist Charles Lyell in helpingDarwin to understand the importance of his fossil vertebrate evidence:

Lyell … in his [1837] presidential address to the Geological Society… drew out the conclusions from Owen’s findings: that fossilfaunas are closely related to their living replacements. … Darwincame down to hear the talk [which] brought home the realimportance of his fossils for the first time. He sensed the closerelationship between extinct megatheriums and glyptodons and themodern sloths and armadillos. Darwin had never expected this; onthe voyage he assumed that he had found European and Africanmastodons and rhinos, not exclusive South American species. Itpulled him up sharp, causing him to ask the key question: why ispresent and past life on any one spot so closely related [emphasisadded]?15

This paper will argue that Darwin did not wait for consultations withLyell and Owen before asking himself this key question. First of all,books in the Beagle library alerted him to a number of suggestiveexamples of fossil vertebrate succession – all from places he visitedduring the voyage. More importantly, he made his own collection offossil vertebrates in southern South America, which, whether by designor by coincidence, put him in a position to test the idea of succession.

14 This literature is enormous. A few examples from my bookcase include: Mayr,

1982, pp. 408–409; Bowler, 1984, p. 154; Bowlby, 1990, p. 208 (who conceded thatDarwin’s doubts about the fixity of species developed during the voyage); Browne, 1995,p. 360; Herbert, 2005, p. 320; Quammen, 2006, p. 27; Browne, 2006, pp. 40–42. David

Oldroyd provided a helpful review of the conversion literature up to 1982. He pointedout that the importance of the role played by Darwin’s fossil mammal collection is nowregarded as less important than it formerly was, and that near consensus has been

reached, placing his conversion after the voyage. See Oldroyd, 1984, especially pp. 360–361. For a pair of recent counterexamples that argue for an earlier conversion, seeEldredge, 2006, pp. 41–44; Eldredge, 2008. Likewise, Kohn et al., 2005, argued thatDarwin ‘‘crosses the threshold between creation and evolution’’ during the last leg of the

Beagle voyage, although his new way of seeing species could only be settled by expertnaturalists (p. 645).15 Desmond and Moore, 1994[1991], p. 210.

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There is evidence enough in his correspondence, his Beagle diary, andhis specimen lists and notebooks to suggest that the patterns ofresemblance between certain extinct fossil vertebrates he collected andsome of the extant, endemic fauna of South America did not escapeDarwin’s notice. On the contrary, his fossil observations during theBeagle voyage mark the starting point of an investigation that wouldlater culminate with Darwin’s ‘‘law of the succession of types.’’16 Lyell’sPrinciples of Geology – which Darwin studied and used as a kind of fieldmanual – argues that fossils are uniquely suited for deriving the lawswhich govern the appearance of new species, so it seems certain thatDarwin wondered why ‘‘present and past life on any one spot [was] soclosely related’’ during the voyage. Darwin pointed to fossil vertebratesuccession as one of the two or three key lines of evidence that per-suaded him of the validity of transmutation. Thus, the timing of hisearliest thinking about fossil succession bears on the history of thedevelopment of his revolutionary ideas about evolution.

Fossil Vertebrate Succession in the Literature

Young, experienced in several branches of natural history, and full ofenthusiasm and ambition for science, Darwin was an ideal choice toserve as unofficial naturalist on the Beagle. Darwin’s Cambridge mentorJohn Stevens Henslow, who had recommended him for the voyage,believed he was well-suited for the natural science enterprise of theexpedition: collecting specimens, observing, and taking copious notes.Darwin was an avid hunter and beetlist. He had learned a great deal ofmarine invertebrate zoology and microscopy from Robert Grant, whoonce ‘‘burst forth in high admiration of Lamarck and his views onevolution’’ while they were collecting together.17 From Henslow’s lec-tures, Darwin learned systematic botany. In his research, Henslowemphasized the importance of delineating natural variation withinspecies, and Darwin embarked on the Beagle with this broader conceptof species firmly in mind.18 Most importantly, he took a crucial geo-logical field excursion through Wales with Adam Sedgwick shortly

16 Darwin, 1839, pp. 209–210.17 C. Darwin, quoted in Egerton, 1976, p. 454. Egerton also noted that Darwin read

his grandfather Erasmus Darwin’s book, Zoonomia, with its ‘‘evolutionary concepts,’’before going off to study in Edinburgh in 1826. An anonymous reviewer of this paper

remarked that ‘‘no grandson of Erasmus Darwin was going to be closed minded on thesubject of development.’’18 Kohn et al., 2005.


before the voyage and was, according to historian James Secord, ‘‘oneof the best-trained men of his age in Great Britain’’ in the geologicalsciences.19 Whatever shortcomings he had as a naturalist would bemitigated by the availability of ‘‘plenty of Books’’ in the Beagle li-brary.20 He made liberal use of these books while his ship was at sea.

By the time Darwin sailed, a number of reports of instances of fossilvertebrate succession had already graced the scientific literature, and atleast three of these appeared in books he is known to have read on theBeagle. For example, one of the earliest known English accounts of fossilvertebrates in South America appears in a book entitled:ADescription ofPatagonia, and the Adjoining Parts of South America which was pennedby Jesuit priest Thomas Falkner and published in London in 1774.21

Falkner’s book describes the many and varied observations made by theauthor during his extensive travels in southern South America, includinga brief but important notice of fossil vertebrates. Falkner wrote:

On the banks of the River Carcarania, or Tercero, about three orfour leagues before it enters into the Parana, are found greatnumbers of bones, of an extraordinary bigness, which seem hu-man…. I myself found the shell of an animal, composed of littlehexagonal bones, each bone an inch in diameter at least; and theshell was near three yards over. It seemed in all respects, except …size, to be the upper part of the shell of the armadillo…. Thesethings are well known to all who live in these countries; otherwise, Ishould not have dared to write them.22

Darwin first read Falkner’s Patagonia sometime on or before 9 July1832, while at sea, headed for Montevideo.23 The Beagle would shortlybe sailing for Patagonia, and Darwin was busy preparing himself for theexperience. In a letter to his sister Susan he wrote:

19 Secord, 1991, p. 133. On Darwin’s training and experience, see also Ruse,

1999[1979], pp. 32–35.20 Henslow, quoted in Desmond and Moore, 1994[1991], p. 101.21 Falkner, 1935[1774].22 Falkner, 1935[1774], pp. 54–55. According to the introduction by Arthur E. S.

Neumann (p. viii), Falkner may have written a four-volume manuscript on his naturalhistory observations in the Americas. The location of this manuscript is not recorded.Falkner’s name is consistently misspelled as Falconer in Darwin’s Journal and Remarks(1839). See Simpson, 1984, pp. 21–22, for some interesting confusion on Simpson’s part

regarding Falkner’s identity.23 A brief entry for 9 (July 1832), ‘‘Rio Corcovado.— Bones. [Falconer],’’ in Dar-

win’s Rio notebook (EH1.10; English Heritage 88202330), p. 47b, establishes this date.

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After laying in fresh water at M[onte] Video, we sail for Rio Negro[Patagonia].- Comparatively near as this is to the civilized world, yetthe whole coast & interior country is totally unknown.- Falcners [sic]account, inaccurate as it must be, is the only one.24

Falkner’s account is particularly interesting because of his explicitcomparison of the fossil remains he found to the living armadillo. Hewas able to make this evaluation despite his lack of training in com-parative anatomy. Darwin, who visited the locality described by Falk-ner later in the voyage, would make the same comparison when hecollected similar specimens (see below). Much later in Origin, Darwinwould write: ‘‘In South America, a [closely allied] relationship is man-ifest, even to an uneducated eye, in the gigantic pieces of armour likethose of the armadillo, found in several parts of La Plata [emphasisadded].’’25

Another example of fossil vertebrate succession in the scientific litera-ture comes from the renowned French comparative anatomist GeorgesCuvier, who named and described the skeleton of another new fossilvertebrate from South America, Megatherium americanum, in 1796. Thecolossal and relatively complete specimen represented, according to Cu-vier, a new genus of edentate closely related to the humble sloths andarmadillos of South America.26 This astonishing conclusion generatedconsiderable excitement in the British scientific community. In 1833,geologist Roderick Murchison called it the most important comparison inCuvier’s four volume work, Recherche sur les ossemens fossiles (1812).27

According to Sandra Herbert, ‘‘substantial portions of Cuvier’s summaryviews were available’’ in Edward Griffith’s English translation, The Ani-mal Kingdom, that was in the Beagle library.28 A supplementary volume,The Fossil Remains of the Animal Kingdom, by Edward Pidgeon, includes alengthy treatment of Cuvier’s Megatherium, with a full page reconstruc-tion of the mounted Madrid skeleton on which Cuvier’s description wasindirectly based (see Figure 1). As forMegatherium, Pidgeon claimed that:

[I]ts examination proves that it had more analogy to the sloths thanto any other beings, especially in regard to the system of dentition

24 Letter, C. Darwin to S. Darwin, 14 July–7 August (1832). See Burkhardt andSmith, 1985, p. 248.25 Darwin, 1859, p. 339.26 See Rudwick, 1997, pp. 27–32, for an English translation of Cuvier’s description.27 See Winslow, 1975, p. 351, note 4.28 Herbert, 2005, p. 303. See also Herbert, 1995, p. 28, for a discussion of the ‘‘rich

pool of ideas,’’ including the notion of ‘‘universal descent,’’ in Griffith’s text.


… and the composition of the extremities. …The general forms ofthe head of the megatherium resemble considerably that of thebradypi [tree sloths]. But the most striking trait of resemblanceconsists in a long descending apophysis, flattened, and situated atthe basis of the zygomatic arch.29

Darwin read this text during the Beagle voyage.30 Additionally, a shortarticle on Megatherium, written by French geologist Louis-ConstantPrevost but based on Cuvier’s work, appears in Bory de Saint-Vincent’sDictionnaire classique d’histoire naturelle, in which the fossil genus ischaracterized as a ‘‘cousin’’ of the tree sloths, partly on the basis of theoddly similar structure of their zygomatic arches.31 Darwin made pro-lific use of all the reference materials on the Beagle, but was especially

Figure 1. A complete reconstruction of Megatherium from a book in the Beagle

library (from Pidgeon, 1830, p. 132).

29 Pidgeon, 1830, pp. 131–133.30 Darwin quoted a phrase from this volume, ‘‘recent observations,’’ with reference to

the alleged link between Megatherium and some ‘‘osseous polygonal plates’’ he collected(see below), in his geological diary (DAR 32.1, p. 66), which suggests that he definitelyhad access to it during the Beagle voyage. The phrase ‘‘late observations’’ in his letter to

Henslow (see below) is a paraphrase of Pidgeon’s text.31 Prevost, 1822–1831, Vol. 10, p. 309. Darwin likely borrowed his phrase ‘‘osseous

polygonal plates’’ (see below) from Prevost’s ‘‘plaques polygons ossifiees.’’

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dependent on this one, writing: ‘‘I am well off in books, the Dic: Class: ismost useful.’’32

A third example of succession appears in Lyell’s Principles of Geol-ogy. Comparative anatomists William Clift (in London) and JosephPentland (then working in Cuvier’s laboratory in Paris) each received acollection of co-mingled and unidentified fossil mammal bones recov-ered from a number of caves in Australia. Both examined the remainsand referred some of them to extinct and others to living representativesof Australia’s endemic marsupial fauna. These results, together with aclear statement about fossil vertebrate succession written by Darwin’sformer professor, Robert Jameson, appeared in a series of brief articlesin the Edinburgh New Philosophical Journal in 1831–1832.33 Lyell thenincorporated these facts into Volume III of his Principles. In discussingthe significance of Australia’s fossil kangaroos and wombats he wrote:

These facts are full of interest, for they prove that the peculiar typeof organization which now characterizes the marsupial tribes hasprevailed from a remote period in Australia, and that in thatcontinent … many species of mammalia have become extinct. Italso appears … that land quadrupeds, far exceeding in magnitudethe wild species now inhabiting New Holland, have, at some formerperiod, existed in that country.34

Darwin was known to have had Lyell’s Volume III in his possession byat least July, 1834, and his enthusiasm for the geologist’s work is leg-endary.

There are two important points to be taken from this literature. First,though the general idea of fossil vertebrate succession was not yet inwide circulation in the early 1830s, some of the facts on which thisgeneralization would later be based were already well known. Darwinwas familiar with these suggestive facts from at least four sources in theBeagle’s library. Lyell discussed a sweeping array of these facts– including new ones brought to light during the Beagle voyage – in hispresidential address to the Geological Society of London in 1837 whichDarwin attended as his invited guest.35 Darwin himself would then bethe first to generalize these facts into his ‘‘law of the succession of types’’

32 Letter, C. Darwin to J. S. Henslow, 18 May–16 June 1832. See Burkhardt and

Smith, 1985, p. 237.33 Pentland, 1831–1832; Jameson, 1831. William Clift’s report appears in Jameson’s

article.34 Lyell, 1830–1833, Vol. III, p. 144.35 Desmond and Moore, 1994[1991], p. 210. See also Lyell, 1837.


in 1839. Owen commented about succession in 1840, in his descriptionof Darwin’s Beagle fossils, and then made a much fuller and clearerstatement on this phenomenon in 1844 (without crediting Darwin orciting Lyell).36 Second, at least some of the resemblance – at a super-ficial level – between recently extinct and extant taxa of South Americawas so apparent that it was not necessary to be an expert comparativeanatomist to notice it. Nor was it necessary to have access to a vastcollection of comparative material at one of the museums of metro-politan Europe. Professional expertise and museum access were neces-sary for verification of specimens, but not for initial recognition.37

Falkner, an amateur naturalist working on the periphery of science,recognized the obvious resemblance between the strange fossil shells andthe living armadillos. So did Darwin.

Darwin’s Vertebrate Fossils

Darwin made a significant collection of vertebrate fossils during histravels in South America. He recognized that many of his specimenswere: (1) new to science; and, (2) extinct. Though his interest in fossilswas mainly geological, he made an effort to identify them and hespeculated on their ecology – or, what Darwin might have called theirplace in the economy of nature – and the cause of their extinction. Intrying to identify his specimens, he compared them to descriptions andfigures of vertebrate fossils and other animals in the Beagle literature,and – more important – to certain representatives of the living fauna ofSouth America. In a few cases, he clearly recognized a similarity. Severalof these specimens corroborated the comparison he read in Falkner’sbook, while others reinforced the idea that recent fossil remains bear aclose resemblance to their living counterparts.

36 Owen, 1840, p. 110; Owen, 1844, p. 240. To be fair, Owen drew some of the

conclusions that led to Darwin’s generalization in the first place, and then he assumed aleading role in discussing the subject comprehensively in the 1840s. Thus, he might havefelt that he did not owe any debt of acknowledgement to Darwin or Lyell. Interestingly,

Nicolaas Rupke argues that this could be the work that convinced a reluctant Owen ofthe fact of transmutation (see Rupke, 1994, pp. 223–224). Nevertheless, it appears thatDarwin was the first to publish this idea in law-like form in his Journal and Remarks(1839).37 I am grateful to historian Richard Bellon, who helped me see this idea more clearly.

See also Camerini, 1997 (especially p. 360) for a brief discussion of the tension between

museum and field work.

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Darwin’s earliest fossil vertebrate discoveries in South America oc-curred in late September 1832, at Punta Alta, a rocky outcrop on thebeach near Bahia Blanca, a struggling frontier village and fort on thecoast southwest of Buenos Aires. While the Beagle rested at anchor inthe bay, he went ashore and found a cache of fossils. His specimensfrom this locality were several, and included a partial skull, which hetentatively identified as ‘‘allied to the Rhinoceros;’’ a disassociatedmandible, bearing a single tooth; and fragments of a bony shell.38 Inearly October, Capt. Robert FitzRoy landed a party about 20 miles eastof Punta Alta with instructions to build a cairn at Monte Hermoso.FitzRoy credits a member of the shore party with the discovery of‘‘many curious fossils in some low cliffs under the mount.’’39 Darwinlater accompanied the captain to this site. There, he had the good for-tune to collect ‘‘some well preserved fossil bones of two or three sorts ofGnawing animals. –One of them must have much resembled the Agoutibut it is smaller.’’ He also noted the local geology.40

In November, Darwin wrote a long letter to Henslow, summarizinghis fossil vertebrate discoveries to date. He craved his mentor’s ap-proval, hinting, ‘‘If it interests you sufficiently to unpack them, I shall bevery curious to hear something about [my fossils].’’ In his letter, hedescribed six fossil vertebrate specimens in some detail, although thefollowing excerpt pertains only to the first three:

I have been very lucky with fossil bones; I have fragments of atleast 6 distinct animals; as many of them are teeth I trust, shattered& rolled as they have been, they will be recognized…. —1st. theTarsi & Metatarsi very perfect of a Cavia: 2nd the upper jaw & headof some very large animal, with 4 square hollow molars.—& thehead greatly produced in front.—I at first thought it belonged ei-ther to the Megalonyx or Megatherium.—In confirmation, of this,in the same formation I found a large surface of the osseouspolygonal plates, which ‘late observations’ (what are they?) showbelong to the Megatherium.41

Darwin also wanted to impress Henslow with his willingness to goagainst the grain of current European scientific thinking. Naturalists in

38 Keynes, 2001[1988], pp. 107–109.39 FitzRoy, 1839, p. 112.40 See Keynes, 2001[1988], pp. 110–111.41 Letter, C. Darwin to J. S. Henslow (ca. 26 October–24 November) (1832). See

Burkhardt and Smith, 1985, pp. 279–281. The phrase ‘‘late observations’’ is a para-

phrase of Pidgeon’s ‘‘recent observations’’ (see note 30).


Europe were then convinced that these enormous fossil shells, or‘‘osseous polygonal plates,’’ as Darwin calls them, belonged to Meg-atherium. Cuvier had come to this conclusion – which would later beshown to be incorrect – on the basis of a report he had received of afossil that he never had the opportunity to examine personally.42 Dar-win, on the other hand, was skeptical about this conclusion, askingHenslow for an account of the ‘‘late observations’’ on which it wasfounded. He had drawn a tentative conclusion, which he shared withHenslow, based on his own observations and bolstered by Falkner:‘‘— Immediately I saw [the osseous polygonal plates] I thought theymust belong to an enormous Armadillo, living species of which genusare so abundant here.’’43 Likewise, in his field notebook, on the day ofhis first Punta Alta fossil discovery, Darwin wrote: ‘‘there is a horizontalbed of earth containing much fewer shells—but armadillo.’’ Later in thesame notebook he observed: ‘‘Megatherium like Armadillo case.’’44

In his geology notes Darwin was much more explicit about theresemblance between the osseous plates he collected and the cases ofliving armadillos. He even took the trouble to speculate about how thesecases might have entered the fossil record:

At Punta Alta the only organic remain I found in the Tosca(excepting mere particles of shell) was a most singular one: itconsisted in an extent of about 3 feet by 2 covered with thickosseous polygonal plates; forming together a tessellated work: itresembles the case of Armadillo on a grand scale: these plates weredouble. or an interval of few inches between them.—With it wasonly a fragment of joint of extremity.—At present the case of thedead Armadillos are oftener found separate from the body. thanconnected with any part.—In this case the envelope of the greatanimal would easily be carried by the water. & by the pressure ofthe Tosca would be doubled up as described.45

42 See Huxley, 1865, pp. 31–43; Rudwick, 1997, 25–32; Herbert, 2005, pp. 303–306 fora history of the misunderstood ‘‘Megatherium’’ hide.43 Burkhardt and Smith, 1985, pp. 279–281. Historian Paul H. Barrett argued that

Darwin was reluctant to theorize about fossils, even in his personal notebooks, afterbeing reprimanded for doing so by Adam Sedgwick during their geological tour ofWales, just before the Beagle voyage (see Barrett, 1974, p. 150). That he was now willing

to speculate so openly to Henslow indicates something about how much Darwin hadmatured by this point as a naturalist. It also demonstrates how much Darwin heldHenslow in high esteem.44 See Barlow, 1946, pp. 166–167.45 CUL-DAR 32.65-66. Portions of this same text are quoted and discussed in Her-

bert, 2005, pp. 304–305.

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As for Cuvier’s identification of these remains with Megatherium,Darwin remained skeptical, but he hedged his bets, noting:

It is stated. that ‘recent observations’ show the Megatherium hadsuch an envelope; it certainly is probable it belongs to some of theanimals the bones of which are so abundant in the gravel.46

Darwin found similar remains elsewhere in South America, but he wasinconsistent in his identifications. He referred to them variously in hisdiary and notebooks as ‘‘Megatherium hide,’’ ‘‘armour,’’ ‘‘armadillolike case,’’ ‘‘shell,’’ ‘‘plates,’’ and, very often, ‘‘Paludo’’ or ‘‘Paludas,’’which are bastardizations of peluda [hairy], a Spanish word for hairyarmadillos of the genus Chaetophractus.

The osseous polygonal plates Darwin collected pertain not to Meg-atherium, but to a member of a related family of extinct, armadillo-likeanimals now called Glyptodontidae (Figure 2). Due to Cuvier’s error,confusion reigned in Europe for a number of years on the identity of theseremains. Bits and pieces of fossil armor sent to Europe for identificationin the 1820s and 1830s were often referred to Megatherium. By 1836,however, a number of naturalists had concluded that the armored ‘‘ani-mal of South America is not the Megatherium and is allied to theArmadillos.’’47 Strangely, William Buckland, in his widely read Bridge-water Treatise of that same year, continued to associate the fossil armorwith Cuvier’sMegatherium. In 1837, Peter Wilhelm Lund established thenew genusHoplophorus for a specimen of the armor and some associatedbones, which, he wrote, were ‘‘closely allied to, if not identical with, the‘Dasypus’ [armadillo].’’48 Owen then established his own new genus,Glyptodon, based on similar remains, in 1838. The upshot of all this is thatDarwin’s hunch about the obvious relationship between the fossil armorand the living armadillos was correct (though whether he was correct ornot does not matter for the purposes of the argument in this paper). Thisexample goes to show that European savants were every bit as capable ofmuddling the fossil evidence as Darwin was. In the case of the dermalarmor, at least, it proved advantageous to be a field naturalist in SouthAmerica, where the fossils were preserved in prolific numbers and theliving comparative materials were scurrying around underfoot. Most ofthe naturalists ‘‘on the ground,’’ Darwin included, noticed the similarity.

46 CUL-DAR 32.66.47 Huxley, 1865, p. 35. Huxley’s authoritative redescription of the osteology of

Glyptodon includes a useful history of this and related fossil genera.48 Quoted in Huxley, 1865, p. 35.


Darwin went on to describe three more fossil vertebrate specimens inhis November letter to Henslow:

3d the lower jaw of some large animal, which from the molar teeth,I should think belonged to the Edentata: 4th. some large molarteeth, which in some respects would seem to belong to an enormousRodentia; 5th, also some smaller teeth belonging to the same order:&c &c.49

These examples, together with the Cavia mentioned previously, serve toshow that Darwin did make an effort to compare his fossil vertebratespecimens with living species in South America and that he did not keephis geological enterprise entirely separate from the zoological. Indeed, itwould not make sense for a naturalist of Darwin’s period to treat geologyand zoology as entirely distinct categories. They also demonstrate thatDarwin was competent enough at comparative anatomy to recognize andappreciate certain similarities between fossil and living species.

In his geology notes, Darwin elaborated on some of the other fossilremains he found in the Bahia Blanca area:

Figure 2. Richard Owen’s ‘‘Gigantic Extinct Armadillo.’’ Sections of armor from

these animals were initially referred to Megatherium. However, many field naturalists,Darwin included, recognized their obvious resemblance to armadillos. Owen’s titleacknowledges this resemblance also (courtesy of the Library of Congress via SandraHerbert).

49 Burkhardt and Smith, 1985, pp. 279–281.

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I could perceive traces of 4 or 5 distinct animals: two of whichcertainly belonged to the Rodentia. One must have been allied tothe Agouti; the tarsi & Metatarsi belong to an animal less than thepresent. common inhabitant, Cavia patagonica. The Agoutis are allproper to S. America; & none have hitherto been found in a fossilstate.50

Note that Darwin knew, even during the voyage, that agoutis are en-demic to South America, and that his was the first and only knownfossil representative of this unusual group of rodents. Eighteenth- andnineteenth-century naturalists, including Darwin’s hero Alexander vonHumboldt, were particularly interested in delineating patterns in thedistribution of plants and animals. According to Michael Paul Kinch, aprimary reason for this interest was because these patterns of distribu-tion were expected to elucidate the question of species’ origins.51

One year later, in late August, 1833, Lt. Bartholomew J. Sulivan as-sumed charge of a shore party, including Darwin, encamped near PuntaAlta for surveying. He patiently indulged Darwin’s compulsion to collectdelaying the entire party while his shipmate waited for low tide to combthe beach for fossils. Several discoveries took place here, including onespecimen embedded in solid rock just at the low-water mark. The lieu-tenant provided men to dig the specimen out while the rest of the party,Darwin included, repaired to Bahia Blanca.52 The commander of thenearby fort toldDarwin that he had ‘‘often seen and heard of largePaludoScales on cliffs,’’ by which he likely meant more examples of the giantosseous polygonal plates.53 The specimens collected on this visit were‘‘more perfect’’ than those found previously, including ‘‘nearly an entireskeleton.’’54 Later in September, near the coastal town of Guardia delMonte, Darwin found ‘‘a perfect piece of the case of theMegatherium.’’55

In October 1833, Darwin searched for fossils north of Buenos Aires,in the locality described by Falkner, near the town of Santa Fe, andalong the Rio Parana. On his way north, he spent a night just outsidethe town of Lujan. The original Megatherium specimen described by

50 CUL-DAR 32.70-71.51 See Kinch, 1980. For a more comprehensive history of biogeography, see Browne,

1983. For more on the global mapping and measuring which was characteristic of‘‘Humboldtian’’ science, see Dettelbach, 1996.52 Sulivan, 1896, pp. 36–43.53 See Barlow, 1946, p. 196.54 Letter, C. Darwin to Caroline Darwin, 20 September (1833). See Burkhardt and

Smith, 1985, p. 331.55 Keynes, 2001[1988], p. 190.


Cuvier had been found in a bank of the Rio Lujan which Darwincrossed the following morning.56 He spent a day searching the cliffs ofthe Rio Carcarvana for fossils, finding and collecting a single, curioustooth. On the Rio Parana, he hired a canoe in an effort to collect somebones jutting from the bank just above the water. Unfortunately, theselarge bones, which he attributed to Mastodon, were very fragile anddifficult to collect – Darwin escaped with only a few skeletal fragmentsand some teeth.57 During this journey Darwin recognized that therewere at least two different types of bony carapace: ‘‘clearly two sorts ofMegatherium—contemporaneous with Mastodon,’’ he wrote, ‘‘case oftaller, two or three inches thick.’’ He also took the trouble to investigatea large ‘‘Paludas case in a Barranca [cliff] of red Tosca—The shellformed a well between 4 and 5 feet across, entire, but soft, no bonesexcept a lump: the bones were said to be less than a full grown cow.’’58 Itis a singular misfortune that Darwin was never able to locate significantskeletal material associated with one of these fossil shells in order tohave something to compare directly with some of the other ‘‘Meg-atherium’’ bones he collected elsewhere. Absent this evidence, theanecdotal account he recorded here established – albeit tentatively –that the missing ‘‘Paludas’’ bones were allegedly less than a ‘‘full growncow,’’ and therefore considerably smaller than a Megatherium (whichPidgeon likened to the size of a rhinoceros59). Lastly, Darwin collected afossil horse’s tooth ‘‘well buried’’ in the ‘‘red compact Tosca.’’60

Stricken with fever during this trip, he returned to Buenos Aires by boatto rendezvous with the Beagle.

A delay in sailing afforded Darwin the opportunity to make anotheroverland collecting trip from Montevideo north to the Rio Negro inNovember. One of his acquisitions there was a large skull purchasedfrom a local landowner.61 In his diary he identified this specimen as ‘‘apart, very perfect, of the head of a Megatherium.’’62 On this trip he alsoobserved, but apparently did not collect, a number of interesting fossils,including: ‘‘Paludas with a tail very heavy and solid, fragment 17 inches

56 Keynes, 2001[1988], p. 191. Darwin neglected to mention the river’s paleontological

significance, something about which he seems to have been unaware. He also seems tohave been unaware of Lujan’s most prominent citizen, Francisco Javier Muniz,Argentina’s first naturalist and first fossil vertebrate collector.57 Keynes, 2001[1988], p. 193.58 Barlow, 1946, pp. 209–210.59 Pidgeon, 1830, p. 35.60 Barlow, 1946, p. 210.61 Darwin, 1839, p. 181. The purchase price for the skull was eighteen pence.62 Keynes, 2001[1988], p. 204.

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long, circumference (longest) 11’’ at end before Vertebra with attach-ments to the case – extraordinary weapon.’’63 Given the specimen’s size,and its unusual description, this could only be another example of agiant bony carapace, this one with a distinctive tail.64

From Montevideo, the Beagle sailed south along the Patagoniancoast, where Darwin fell on some hard luck. He spent Christmas, 1833,at Puerto Deseado, but he found no fossil vertebrates. Early in January,1834, the Beagle reached Puerto San Julian, where he noted a distinctstratum filled with gigantic fossil oysters. On a terrace above the cliffface, in a relatively young deposit of earthy matter, he collected someincomplete post-cranial fossil mammal material, which he tentativelyidentified as another Mastodon. Thereafter, the Beagle departed, andDarwin never collected another fossil mammal.65

What can we make of Darwin’s work with vertebrate fossils duringthe voyage? Too much has already been made of his so-called mistakesand misidentifications. First of all, field identifications are necessarilyprovisional under almost any circumstances. Darwin’s fossils werefragmentary and at least partially obscured by matrix. His workingconditions on the Beagle were difficult, at best. He had few comparativematerials to work with. Worst of all, almost everything he collected wascompletely new to science. It is not reasonable to fault Darwin forfailing to recognize fossil taxa that previously had never been describedand named. By the time the Beagle sailed, only two fossil genera knownto occur in South America, the celebrated Megatherium and the nearlyubiquitous Mastodon, had been described in the scientific literature.66 Itshould therefore be no surprise that Darwin attributed a significantnumber of his fossils to these two taxa.67

Darwin acknowledged his own limits as a vertebrate zoologistreferring once in a letter to Henslow to his ‘‘entire ignorance of com-parative Anatomy.’’68 He treated his field identifications of fossil ver-

63 Barlow, 1946, p. 216.64 I am grateful to vertebrate paleontologist Darin Croft, who helped with this con-

clusion.65 Simpson, 1984, pp. 30–31. Darwin did, however, play a role in promoting further

fossil vertebrate exploration in South America (see Brinkman, 2003).66 Owen, 1840, pp. 13–14 cites the Megatherium as well as three species of Mastodon.

See also Simpson, 1984 for the state of vertebrate paleontology in South America beforeDarwin.67 Interestingly, Sulloway (1969, pp. 91–92) made the same point while arguing that

Darwin ‘‘knew little about paleontology.’’68 Letter, C. Darwin to J. S. Henslow, March 1834. See Burkhardt and Smith, 1985, p.

368.


tebrates as tentative and routinely expressed doubts about them in hisnotes and letters. For want of comparative material, he was often re-duced to mere guesswork. One specimen, for example, he identified onthe basis of its size and solidity, writing: ‘‘At Port St Julian I found somevery perfect bones of some large animal, I fancy a Mastodon.—thebones of one hind extremity are very perfect & solid.’’69 In some noteswritten later in the voyage, however, he recorded his uncertainty aboutthis specimen, largely on what we would call ecological grounds:

Is the animal of St Julian a Mastodon? Even if a change of climatecould be granted it is scarcely possible to believe the plains of gravel[in Patagonia] ever could have supported a much more luxuriantvegetation[.] We must suppose like the Camel of Eastern climes orthe Guanaco which now lives here that it was fitted for a stuntedVegetation.70

Darwin found this particular specimen in some very recent deposits andconfessed that he had ‘‘no idea at the time, to what kind of animal theseremains belonged.’’71 It is interesting that in speculating about the fossilanimal’s adaption to its environment he should compare it to the gua-naco, one of the very few large terrestrial vertebrates living in Pata-gonia. He had an abundance of guanaco bones at his disposal duringthe voyage. Perhaps he compared his fossil to these remains and foundno morphological resemblance. Still, the fact that he compared them inany respect might help explain why he was so profoundly impressed byRichard Owen’s later identification of this fossil as an ‘‘extinct Gua-naco’’ – another example of fossil vertebrate succession (which was latershown to be false).72 Had Darwin anticipated this result?

Despite his shortcomings as a paleontologist, Darwin’s record of fossilvertebrate identifications is remarkably good. According to Owen,Darwin’s collection from South America comprises ten great quadrupedsand at least two rodents, mostly new to science which will be discussed inthe order in which Owen described them. First, Darwin collected thecomplete skull and lower jaws of Toxodon platensis (Figure 3); and somemiscellaneous post-cranial material of Macrauchenia patachonica(Figure 4). Darwin tentatively identified these as Megatherium andMastodon, respectively. These are arguably his two most notorious

69 Darwin to Henslow, March 1834 in Burkhardt and Smith, 1985, p. 369.70 CUL-DAR 42.99.71 Darwin, 1839, p. 208.72 See Rachootin, 1985; Herbert, 2005, pp. 320–324. The phrase ‘‘extinct Guanaco’’ is

Darwin’s.

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‘‘misidentifications.’’ But his error makes sense when one considers thatthese were the first specimens ever found of two very unusual orders ofextinct mammals unique to South America (which would later be calledNotoungulata and Litopterna). Darwin identified the rest of his fossilvertebrates more-or-less correctly. He referred a number of specimens

Figure 3. The skull and palate of Toxodon platensis. (From Owen, 1840, Plate I,reproduced with permission from John van Wyhe ed., The Complete Work ofCharles Darwin Online (http://Darwin-online.org.uk/).).


http://Darwin-online.org.uk/

to Megatherium, Megalonyx, or to an ‘‘edentate,’’ including: a skullfragment of Glossotherium sp. (Figure 5); a lower jaw and teeth ofMylodon darwinii (Figure 6); a partial skeleton of Scelidotherium

Figure 4. Foot bones from Macrauchenia patachonica. (From Owen, 1840, Plate XI,reproduced with permission from John van Wyhe ed., The Complete Work ofCharles Darwin Online (http://Darwin-online.org.uk/).).

PAUL D. BRINKMAN384


Figure 5. Skull fragments of Glossotherium sp. (From Owen, 1840, Plate XVI, repro-duced with permission from John van Wyhe ed., The Complete Work of Charles

Darwin Online (http://Darwin-online.org.uk/).).



Figure 6. Lower jaw of Mylodon darwinii. (From Owen, 1840, Plate XVIII, repro-

duced with permission from John van Wyhe ed., The Complete Work of CharlesDarwin Online (http://Darwin-online.org.uk/).).

PAUL D. BRINKMAN386


leptocephalum (Figure 7); a lower jaw ofMegalonyx jeffersonii (Figure 8);and a skull of Megatherium cuvieri (Figure 9). All five of the aforemen-tioned genera are similar in appearance. All are giant ground sloths andmembers of the order Edentata (Xenarthra). The first three were new toscience, the fourthwas very poorly known, and only the last was relativelywell known. Small wonder that Darwin could not distinguish them. Healso collected some dermal armor and two small bones, which Owenidentified as ‘‘Large Edentata’’ (Figure 10) (probably referable toHoplophorus). Darwin often followed European scientific opinion byreferring these remains to Megatherium, but, as noted above, he recog-nized the resemblance of the dermal armor to armadillos, and he oftenprivately referred to them as such. He also correctly identified the molarof an extinct horse, Equus sp. (see Figure 10) and the teeth and skeletalelements of a Mastodon, which Owen referred to Mastodon angustidens.Other fossil remains he recovered at Monte Hermoso and Punta Alta

Figure 7. Skull and teeth of Scelidotherium leptocephalum. (From Owen, 1840, PlateXXI, reproduced with permission from John van Wyhe ed., The Complete Work of

Charles Darwin Online (http://Darwin-online.org.uk/).).



Figure 8. Lower jaw of Megalonyx jeffersonii. (From Owen, 1840, Plate XXIX,reproduced with permission from John van Wyhe ed., The Complete Work of


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Figure 9. Skull fragments of Megatherium cuvieri. (From Owen, 1840, Plate XXX,reproduced with permission from John van Wyhe ed., The Complete Work of




included a jaw and hind foot of an extinct member of Ctenomys (seeFigure 10), an extant genus of rodent endemic to South America; and amolar and bony fragments (see Figure 10) of an unnamed animal

Figure 10. Sections of dermal armor and toe bones of Hoplophorus (top); Equus sp.tooth (lower left); and teeth, jaw, and foot bones of Ctenomys. (From Owen, 1840,Plate XXXII, reproduced with permission from John van Wyhe ed., The Complete

Work of Charles Darwin Online (http://Darwin-online.org.uk/).).

PAUL D. BRINKMAN390


resembling the capybara, another extant rodent of unusual size. Darwinidentified these remains as agoutis and unspecified rodents.73

The Lyellian Context for Darwin’s Work

Darwin’s interest in fossil vertebrate succession, as well as the rest of hisgeological research program, was profoundly influenced by a carefulreading of Lyell’s Principles of Geology during the course of the voyage.Henslow had recommended bringing Lyell’s first volume – recentlypublished – but ‘‘on no account’’ to accept all of its views. Darwindevoured the book at sea, and then read the second and third volumesas soon as they were sent to him in South America. He found thegeologist’s uniform approach – soon dubbed ‘‘uniformitarianism’’ – sohelpful in disentangling the geological problems he encountered on thevoyage that by the time he had reached Peru he considered himself a‘‘zealous disciple’’ of Mr. Lyell.74

Lyell’s second volume, which Darwin received in 1832 in Montevi-deo, is a book-length treatise on earth’s organic processes, and anespecially critical appraisal of Jean Baptiste de Lamarck’s transmuta-tion theory. Lyell was bound by his own actualistic approach to rejecttransmutation on the grounds that it has never been seen to occur – noteven in the mummified remains of animals collected in Egypt. Yet heconceded that one advantage of Lamarck’s theory is that it precludesthe repeated appeal to a ‘‘First Cause’’ to explain the appearance of newspecies. Lyell argued that the successive extinction of species is a con-stant and regular process of nature, much like erosion or deposition. Inorder to maintain a stable system, he had to account for the regularappearance of replacement species. But because he could not appeal toany known ‘‘cause now in operation,’’ he was forced to argue that theappearance of new species is sudden, and so uniformly distributed intime and space, that it would be extremely unlikely for a naturalist toobserve it. Lyell’s readers are left to infer that there is, as yet, anunknown secondary cause for the origin of species.75

73 For the original descriptions on which this paragraph is based, see Owen, 1840.74 Desmond and Moore, 1994[1991], pp. 108, 168. On Darwin’s relationship to Lyell,

see also Browne, 1995, pp. 186–187, 189–190; Herbert, 2005, pp. 63–70; Secord, 1991,pp. 150–153.75 Lyell, 1830–1833, Vol. II, pp. 169–179. See also Cannon 1961; Rudwick, 1970, pp. 18–

21; Rudwick, 1976[1972], pp. 181–183; Ruse, 1999[1979], pp. 77–78. Ruse writes (on p. 78):

‘‘This is how Lyell’s friends and critics read him, and he agreed with this interpretation.’’


Lyell concludedChapterXIof the secondvolumewithadiscussionof thepotential role of fossils in finding this unknown secondary cause. He wrote:

Naturalists may, in the course of future centuries, accumulate po-sitive data, from which an insight into the laws which govern [theappearance of new species] may be derived…. [G]eological monu-ments [i.e., fossils] alone are capable of leading us on to the dis-covery of ulterior truths. To these, therefore, we must now appeal,carefully examining the strata of recent formation wherein the re-mains of living species, both animal and vegetable, are known tooccur. We must study these strata in strict reference to theirchronological order as deduced from their superposition, and otherrelations. From these sources we may learn which of the species,now our contemporaries, have survived the greatest revolutions ofthe earth’s surface; which of them have co-existed with the greatestnumber of animals and plants now extinct, and which have madetheir appearance only when the animate world had nearly attainedits present condition.

From such data we may be enabled to infer whether species havebeen called into existence in succession or all at one period; whethersingly or by groups simultaneously.76

This is precisely the kind of investigation that Darwin was undertakingwith his vertebrate fossils. In a March, 1834 letter to Henslow, he de-scribed the geological context for his fossil vertebrate work and noted acurious example of succession involving the bones of an agouti:

I am quite astonished that such miserable fragments of the Meg-atherium should have been worth all the trouble Mr Clift has be-stowed on them. …[A] part were found in a gravel with recentshells, but others in a very different bed.—Now with these latterthere were bones of an Agouti, a genus of animals I believe nowpeculiar to America & it would be curious to prove some one of thesame genus coexisted with the Megatherium.77

Why was Darwin so ‘‘curious’’ about his agouti fossil? In notes that dateto the latter part of the voyage, Darwin wrote speculatively about thegradual birth and death of species, making specific reference to Lyell:

76 Lyell, 1830–1833, Vol. II, p. 183.77 Darwin to Henslow, March 1834 in Burkhardt and Smith, 1985, p. 368.

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With respect then to the death of species of Terrestrial Mammaliain the S. part of S. America. I am strongly inclined to reject theaction of any sudden debacle.— Indeed the very numbers of theremains render it to me more probable that they are owing to asuccession of deaths, after the ordinary course of nature.— AsMr Lyell supposes Species may perish as well as individuals; to thearguments he adduces, I hope the Cavia [agouti] of B. Blanca willbe one more small instance, of at least a relation of certain generawith certain districts of the earth. This co-relation to my mindrenders the gradual birth & death of species more probable.78

Historian Dov Ospovat argued that Darwin here invoked a kind ofLyellian environmental determinism to explain the appearance of newspecies. Lyell supposed that the tight relationship between animals andtheir environments could make sense of the regular extinction andreplacement of species: as environmental conditions gradually change,animals adapted to those conditions disappear, while new ones arise,better adapted to the changed conditions, to take their places.79 Ofcourse, this is, at best, an incomplete solution to the problem of theorigin of new species. It begs the question: where do new species comefrom? Are they formed from organic material? From the dust? MichaelPaul Kinch, who calls Lyell’s hypothesis ‘‘natural creation,’’ argued thatthose nineteenth century naturalists seeking a naturalistic explanationfor global patterns of distribution of species (past and present) foundLyell’s idea to be no more credible than special creation. Why? Becausehis theory called for the sudden appearance of new species yet it did notprovide a mechanism.80 Nor was Darwin satisfied with such a theory.Though Darwin’s remarks about his agouti fossil are not openlytransmutationist, they nevertheless show him contemplating his ownexample of fossil vertebrate succession in the context of the gradualappearance of new species. Given what he claimed about the importantrole of succession in inspiring his speculations on the origin of species, itseems certain that Darwin was privately contemplating transmutationby this point of the Beagle voyage.

Because Darwin left no reliable record, no ‘smoking gun,’ it isimpossible to date precisely the moment of his switch to transmutation-ism. Consequently, it is no longer tenable to pit the early conversion

78 CUL-DAR 42.98.79 Ospovat, 1995[1981], pp. 24–25. See also Rupke, 2005 for a discussion of

‘‘autochthonous generation.’’80 Kinch, 1980, pp. 113–117.


hypothesisagainst the late conversion hypothesis as thoughoneor the otheris correct. Instead, it seems clear that Darwin’s adoption of transmuta-tionism, like the elevation of the plains of Patagonia, happened gradually,by degrees. The record shows that hewas ‘‘greatly struck’’ inMarch, 1837,and that he opened his first transmutation notebook in July, after con-sultations with expert naturalists on the nature of his Beagle specimens.But does this represent themoment of his conversion, or his conviction? Isit the moment he became personally convinced of the fact of transmuta-tion, or the moment he realized he had the means to convince his fellownaturalists of the fact of transmutation, or something else?

Darwin filled hundreds of pages with notes on his observations ofnature during the Beagle voyage and spent his idle shipboard hourscontemplating their possible explanations. When he returned to Eng-land, expert naturalists verified many of his observations and leantadditional credibility to his speculations on the mechanisms of nature.Owen’s conclusions about the fossil vertebrate evidence, for example,did not strike Darwin like a bolt from the blue. Rather, Owen’s workconfirmed an idea that Darwin had already conceived during longmonths – even years – of private speculations about the curious natureof his specimens. Fossil vertebrate succession is a phenomenon thatDarwin recognized on his own and the idea ‘‘haunted’’ him.81 It led himto speculate about the gradual appearance of new species during thevoyage. It led him to ask ‘‘why is present and past life on any one spotso closely related?’’82 Lyell’s notion of ‘‘natural creation’’ was onepossible answer to this question, but one that raised many new prob-lems. Transmutation was the only other naturalistic alternative. Darwinwas already familiar with the idea of transmutation from several sour-ces, including his grandfather Erasmus Darwin’s Zoonomia. He hadread Lyell’s book-length refutation of Lamarck’s transmutation theoryduring the voyage. But he was not so awed by Lyell that he refused tocall the geologist’s conclusions into question on occasion.83 Moreover,Lyell’s book showed that the idea of transmutation deserved seriousconsideration in light of the geological evidence and Darwin had newevidence to consider. Transmutation, therefore, must have been one ofthe possible secondary causes that Darwin weighed to explain the pat-tern of fossil succession. That he never recorded this heretical notiondirectly in his notebooks, diary or letters only shows that he was alreadykeeping it fairly close to his chest – his records were, after all, subject to

81 Darwin, 1959[1887], Vol. 1, p. 67.82 Desmond and Moore, 1994[1991], p. 210.83 Darwin’s theory of coral reef development is a perfect example. See Stoddart, 1976.

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the scrutiny of Capt. FitzRoy.84 Nevertheless, it was the contemplationof fossil vertebrate succession, during the voyage, which set Darwin onthe path to transmutation.

Conclusion

Because Darwin emphasized the role of fossil vertebrate succession ininspiring him to contemplate the origin of species, the question of whenand how he first recognized the phenomenon is crucially important. Ashipboard familiarity with the concept of succession, for example, raisesthe possibility (again) that Darwin was seriously contemplating trans-mutation during the voyage. If so, then historians need to reconsider therole of London’s expert naturalists in enabling his adoption of thetransmutationist hypothesis. Most historians argue that Darwin’sswitch could have taken place only with the aid of experts in metro-politan London, and that he was incapable of understanding thetransmutationist implications of his specimens on his own. On thecontrary, it could be that travel on the periphery and distance awayfrom the scrutiny of expert naturalists gave Darwin the autonomy heneeded to speculate freely about species’ origins. In that case, the truerole of the experts – after the voyage had ended – was in helping Darwinto fashion the argument and to marshal the evidence necessary toconvince the wider scientific community of the fact of transmutation.

A re-evaluation of the role of the fossil vertebrate evidence paints anew, unorthodox picture of Darwin’s work on the species question.Historians and scientists alike should recognize that the actual rela-tionships between the fossils he collected and the extant fauna of SouthAmerica are irrelevant. The only relevant question is: what did he thinkabout possible relationships? The historical record shows that the fossilvertebrate evidence played an early and important role in convincingDarwin personally of the impermanence of species.

84 Sandra Herbert has argued that ‘‘an unrecorded presence may still be a presence(Herbert, 2005, p. 297).’’ There are many reasons why Darwin might have chosen to

leave transmutation out of his notebooks. It is worth noting that Alfred Russel Wallace,who, like Darwin, was also convinced of the fact of transmutation by the spatial andstratigraphical succession of species, also neglected to record his ‘‘great moment of

illumination’’ about his species theory in his field journals (see Raby, 2001, p. 132).


Acknowledgements

This paper originated as a project in John Beatty’s ‘‘Darwinian Revo-lution’’ course at the University of Minnesota. I am most grateful toJohn, David Sepkoski, Michel Janssen, other Minnesota friends andcolleagues, and especially Richard Bellon for many critical discussionsof this topic, as well as some very helpful feedback. Three anonymousreviewers also made many valuable suggestions. I am likewise gratefulto the Columbia History of Science Group/Friday Harbor meetingparticipants of 2003 for their lively and (mostly) hostile reaction to anearlier version of this paper. Rick Madden and David Quammenmotivated me to take-up this project again after a long hiatus. There-after, I benefited from an exciting and enlightening discussion on thissubject with Niles Eldredge. Two web resources, ‘‘The CompleteWork of Charles Darwin Online’’ (http://darwin-online.org.uk/) and‘‘Darwin Correspondence Project’’ (http://www.darwinproject.ac.uk/)have been immeasurably helpful in providing easy access to essentialDarwiniana. Vince Schneider gave me the time to work on this paper.Lori Belk helped me with the figures. Nancy Loquet translated a diffi-cult French text for me. Darin Croft advised me on the fossils. JanetEdgerton, Librarian at the North Carolina Museum of NaturalSciences, filled my unusual book and article requests. ChristineGiannoni, Associate Librarian at The Field Museum, provided manyhelpful services while I worked on this project in Chicago. Finally,thanks to the attentive staff of the Player’s Retreat in Raleigh, wherethe better part of this paper was written.

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