Darwin and the "mega-theria" of Patagonia


Richard Owen's restoration of Glyptodon. From Brinkman (2009).

ResearchBlogging.org Perhaps one of the primary reasons that there is so much to say about Charles Darwin is that he left us so much material to scrutinize. Outside of his famous printed works there are numerous notebooks and a staggering amount of personal correspondence which are constantly being parsed for insights into how he formulated his evolutionary ideas. Indeed, there is still scholarly debate about when Darwin embraced the idea of evolution and what observations spurred him to that intellectual turning point, and a new paper by Paul Brinkman examines the role fossils played in the young naturalist's transformation.

According to many recent biographies Charles Darwin did not fully give up the idea that species were fixed entities until about July of 1837, a little less than a year after he returned to England from his voyage aboard the HMS Beagle. This change is often credited, in part, to the conclusions professional London naturalists had made about specimens that Darwin had collected. Though he was an enthusiastic naturalist Darwin did not have the background in comparative anatomy, paleontology, or other sciences necessary to fully understand the fossils he recovered in South America. Instead he relied on the analysis of experts, like the anatomist Richard Owen, to make the connections between the extinct forms represented by the fossils and the modern Patagonian fauna.

Much of this case rests on the mistakes Darwin made in his attempts to identify the fossils. Darwin grouped nearly all the large fossils he found into two genera, Megatherium and "Mastodon", even though many of the bones turned out to represent entirely new creatures. Clearly Darwin was no expert paleontologist, but as Brinkman argues we should be careful in our criticism of Darwin's science. During Darwin's time Megatherium and "Mastodon" were the only large extinct mammals known from South America. Given that Darwin was working with the fragmentary remains of previously unknown kinds of mammals, like Toxodon and Macrauchenia, it is not surprising that he did not immediately recognize them as something new. Darwin did make good use of the Beagle library during his studies, but he lacked adequate resources to compare these strange mammals to.

Darwin also drew comparisons between some fossils and critters that scurried around the pampas. In his forays into the field Darwin often found polygonal plates that were often attributed to the giant sloth Megatherium. As Darwin knew, however, this hypothesis was controversial and the little bits of armor were very similar to that of the living armadillos of South America. This was confirmed when Owen attributed them to a new genus, Glyptodon, which he restored as a giant, extinct armadillo. This fed into what Darwin called the "law of succession of types", for the extinct Glyptodon was clearly related to the living armadillo from the same region. Some sort of species death (and possibly birth) had happened in the past.

But did these fossils influence Darwin's views on the transmutation of species? While it is impossible to definitively identify what caused the change in Darwin's thinking in the summer of 1837, the fossils from South America likely contributed to his early considerations of evolution. If the giant fossils he found spoke to the "death" of species, for example, what could explain the "birth" of new species we are familiar with today? Furthermore, why were the extinct forms he discovered closely allied to modern species? There was clearly a succession of animal types that took place, but what was the process that explained the pattern? Naturalists of various stripes hinted that there was some secondary cause that could simultaneously account for both these questions, but during the 1830's the nature of that mechanism was mysterious.

Such questions were actively considered by Darwin, and Brinkman cites evidence from Darwin's notebooks and correspondence that the young scientist was already beginning to contemplate them during the Beagle excursion. Even more importantly, despite some of his errors in identification, Darwin did make some attempt to understand the fossils he found and was not entirely reliant on the opinions of London anatomists. The conclusions of the urban academics served more to confirm and solidify questions that Darwin was already thinking about; the young Mr. Darwin was not entirely naive about fossils and the succession of forms through time.

Brinkman, P. (2009). Charles Darwin's Beagle Voyage, Fossil Vertebrate Succession, and "The Gradual Birth & Death of Species" Journal of the History of Biology DOI: 10.1007/s10739-009-9189-9

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Why is this so novel that it's worth shelling out $34.00? It seems to be setting up strawman arguments, when modern biographies don't paint such a polarised picture, as far as I can recall.

Contrary to the impresssion given by the abstract, it's well known that Darwin recorded his thoughts doubting fixity of species around July 1836, when he was still on the voyage, and in the diary he started in August 1838 he recalled having "been greatly struck from about [March 1836] on character of S. American fossilsâ& species on Galapagos Archipelago.âThese facts origin (especially latter) of all my views". Yes, he speculated on species extinction earlier, while still in South America. So, what's new that isn't in the Wikipedia article on the "Second voyage of HMS Beagle"?

By dave souza (not verified) on 25 Jun 2009 #permalink


1) There's always the university library, or you could ask someone with access, of course. Even I wouldn't pay $34.00 for a paper.

2) The quote you mention is cited in the paper and is from 1837, not 1836. Brinkman cites it to highlight two competing versions of when Darwin starting thinking about evolution which Darwin himself played into by penning conflicting accounts.

3) Many biographical treatments of Darwin (which are cited in the paper) say that Darwin relied on the opinions of London naturalists to understand the fossils he had found. What Brinkman documents is that while Darwin was no vertebrate paleontologist he did attempt to compare the material to what was known and made connections between some of the fossils and forms living in South America. Traditionally it has been said that this realization only came after the anatomists in London had studied Darwin's fossils and told him so.

Perhaps I did not fully do justice to the paper here, but I think it is an interesting investigation to a part of Darwin's early studies that are often glossed over or viewed through a modern lens. If you wish I can send the paper to you, but it might be wise to avoid asserting that a paper is setting up straw man arguments based upon an abstract alone.


1) Us impoverished people out in the sticks, without access to university libraries... the paper does sound interesting and I would love to see a copy of it.

2) The first quote I mention, "If there is the slightest foundation for these remarks the zoology of Archipelagoes â will be well worth examining; for such facts [would inserted] undermine the stability of Species", is from Darwin's ornithological notes and is generally dated to the last lap of the voyage, around July 1836. The second quote begins "In July opened first note Book on "transmutation of Species". â Had been greatly struck from about month of previous March on character of S. American fossils" and is from the diary which Darwin began in August 1838 with notes on earlier events in his life. Although Darwin Online catalogues the page "[13 recto] [1838]", it faces and follows on from the page dated 1837, and all the other events in it can be dated to 1837. The year 1838 appears on the next page, which is catalogued as [13 verso] [1838]. So, Darwin is pretty clearly referring to his Notebook B: [Transmutation of species (1837-1838)] being started in July 1837, and to having been struck from March 1836. The paper may have a different interpretation, but the usual one seems pretty sound to me.

3) Desmond & Moore p. 210 of their ''Darwin'' are quite wrong about the fossils, saying that "on the voyage he assumed he had European and African mastodons and rhinos", so Brinkman's point is valid there. Janet Browne's ''Voyaging'' p. 224 gives an accurate account of how Darwin identified the fossils while on the voyage, including mention of him noting the armadillo-like carapace which he misidentified from his books as belonging to the Megatherium. In 2006 Niles Edredge wrote an article going into the various issues in some more detail, and like Brinkman feels that too much stress has been laid on the findings of the experts in London.

So, there is validity in the approach suggested in the abstract, but the way it's worded suggests a little hype about novelty which may be misplaced. It is a good point that the influence of the fossils on Darwin tends to be underrated â I was annoyed by the recent Richard Dawkins' "Genius of Charles Darwin" documentary which started with Darwin on the Galapagos, wrongly suggesting he'd noticed that the finches differed, and then implied by the sequence of the programme that it was afterwards that Darwin found the fossils. Still, guess that was just a TV programme by a non-historian. Any new analysis setting the record straight is welcome, and it will be interesting to see if there are any findings that overturn the current thinking of historians.

By dave souza (not verified) on 26 Jun 2009 #permalink

Update for interim clarification â there's a lot of value in Paul Brinkman's thoughts, and it's a properly referenced paper rather than just a magazine article so an excellent focus on an area well worth exploring. It's essentially a subtle point as to whether Darwin's June 1836 questioning the stability of species was a first hint of doubt, or a glimpse of evolutionary musings he'd commenced while still in South America but had not put in writing for reasons of secrecy.

I've doubts about how far Paul is right, but it's subtle and complex and at the least there are interesting questions being asked. One such is the issue of whether "Had been greatly struck from about month of previous March" means March 1837, as he claims some historians have stated, or March 1836 which looks more probable grammatically to me, and is clearly Nora Barlow's 1933 interpretation.

So far I've not found anyone interpreting it to claim that Darwin didn't begin his speculations until March 1837, but perhaps I'm missing something. The research continues, essentially Paul's paper is a great resource.

By dave souza (not verified) on 26 Jun 2009 #permalink

Having gone into this a bit more, your summary is good, but recent publications by historians cover much of Brinkman's argument, and show full awareness that Darwin was thinking about the fossil succession through the voyage. The difference is that they think that Darwin's ideas went through a slow and intermittent development, to the point where he clearly doubted fixity of species when writing the famous ornithological notes passage around June 1836, but still wanted expert opinion on the distinction between varieties and species to solidify that doubt.

For example, "If anywhere can be said to be the geographical source of Darwin's doubting the fixity of species it is the South American mainland, where he had been struck by the key relationships between fossil and recent mammals and between the various 'representative' species of living mammals and land birds such as the rheas. These crucial observations, combined with his study of Lyell's Principles, prepared Darwin's mind for a break with received wisdom on species origins, as he himself stated in the opening lines of Origin and as he explained with great clarity in the introduction to Variation"
"The idea that a species could adapt to a minor extent to suit new surroundings was a commonplace and did not entail a belief in transmutation.... It was facts such as the fossil mammals from Patagonia together with the Falkland Foxes and the different kinds of birds and tortoises on different islands of the Galápagos that probably stirred such doubts. Once John Gould pronounced the mockingbirds as separate species in February 1837, about four months after the Beagle reached Falmouth, the break with Lyell's view probably seemed to Darwin to be inescapable".

Brinkman goes further in believing that during the voyage Darwin considered transmutation as an explanation of the fossil succession, but did not write anything down in case FitzRoy read it. This is unknowable, and countered by the details of Darwin's speculations differing significantly from the transmutationist views he'd been briefly exposed to in Edinburgh. As shown in Bowler's "Evolution, The History of an Idea", Lamarck (and to some extent Grant) thought species developed in parallel, with species on a line of development grading indistinguishably into one another without any extinction. Darwin's developing views were very different. As to whether Darwin's diary means that his ideas changed in March 1836 or March 1837, my reading seems to be a minority view which I'll reconsider.

Brinkman's description of historians claiming that Darwin didn't begin his speculations until March 1837 does apply to Sulloway's 1982 paper at
on "Darwin's Conversion: The Beagle Voyage and Its Aftermath", but Sulloway's "Darwin's Early Intellectual Development: An Overview of the Beagle Voyage" of 1985 analyses a gradual development. Sandra Herbert's 1980 discussion of the Red Notebook does attribute a March 1837 date for the origin of Darwin's new views on species to hearing the from recognised zoologists what they meant by a species in relation to his own collections.
However, Sandra Herbert's 1995 assessment of an essay from around 1834 is that Darwin was then developing a "narrative framework for the history of life on the continent" in a presentation which "is not transmutationist, but it is highly sequential".

In conclusion, historians have already agreed that fossil vertebrate succession was one of the key lines of evidence that led him to question the ï¬xity of species, but it by no means "seems certain that he was seriously contemplating transmutation" during the Beagle voyage in the way that Brinkman claims. His rousing call that "historians of science need to reconsider both the role of Britainâs expert naturalists and the importance of the fossil vertebrate evidence in the development of Darwinâs ideas on transmutation" is a bit over the top, historians are reviewing and reconsidering these factors, but not reaching the same conclusion as him on the pace at which Darwin's ideas developed. All we know for sure is that Darwin clearly doubted fixity of species when writing the famous ornithological notes passage around June 1836, and gave full credence to his own version of transmutation in March 1837, though still rejecting Lamarck's ideas.

By dave souza (not verified) on 30 Jun 2009 #permalink