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Bishop Pontoppidan Versus the Tree Geese

by Daniel Loxton, Feb 08 2011
Portrait of Erich Pontoppidan

Erich Pontoppidan

Steve Novella's discussion of gullibility about fictional tree octopi reminded me of the curious case of the “Tree Geese” investigated by the Right Revered Erich Pontoppidan, Bishop of Bergen in Norway from 1747 to 1754.

Skeptical history (dimly) remembers Pontoppidan as a pivotal early proponent of the “Great Sea Serpent” of the North Atlantic. Although he was perhaps the person most responsible for moving sea serpents out of the realm of mythology and into what we would now call cryptozoology,1 Pontoppidan is largely eclipsed by more recent sea monster authors (Oudemans in particular). When he is remembered at all, Pontoppidan carries a reputation for credulity. His two-volume Natural History of Norway, translated from Danish to English in 1755, promoted not only the “great Sea snake, of several hundred feet long” but also the Kraken. He even argued for the existence of mermaids!

We'll come back to sea monsters at another time. Today I'd like to look at Pontoppidan himself. It's perhaps understandable if some suppose that a creationist mermaid-believer might be a lightweight. Luckily (for skeptical researchers love nothing more than seeing our assumptions turned on their heads) Pontoppidan turns out to have been much more complicated than his place in cryptozoological history suggests.

Science Advocacy

Mermaids or no mermaids, the Bishop of Bergen was a scientist — and indeed, a case could be made to count him as an early scientific skeptic. A member of the Royal Danish Academy of Sciences, Pontoppidan articulated pro-science positions that many skeptics would recognize today:

I am therefore inclined to think, that neither I nor my brethren transgress the bounds of our ministerial office, by investigating and exhibiting natural truths concerning the works of God, which, like his word, are Jehova’s. I am rather of opinion, that a supercilious neglect of such truths, in this critical age, as one the causes of that contempt, with which the freethinkers, as they arrogantly stile themselves, look on the ministerial function.2

He had a specific recommendation to fix this neglect of truth.

I heartily join with the celebrated Linnaeus in wishing, that even those gentlemen in the universities, who are not particularly destined to physic, or the like, but to the study and promulgation of the word of God, in some ministerial office, were directed to apply such a part of their academic years to physics, as may equal, if not exceed the time spent in metaphysics….3

As a bishop, he of course emphasized the argument that scientific research supports natural theology. At the same time, Pontoppidan made modern-sounding arguments for the earthly utility of science. Scientific literacy would help clergy to “to make useful discoveries or improvements, from the products of nature, to the lasting benefit of their country,” as well as to communicate the majesty of creation. His advocacy of scientific medicine may sound familiar to modern skeptics.

The utility, I should say the absolute necessity of this science to medicine, needs no tedious proof, the alliance between natural philosophy and medicine being universally known, and the whole materia medica being properly res physica.4

He was a guy with a lot of questions. Almost a century before Lyell's Principles of Geology, Pontoppidan understood that there were serious problems with flood geology. A fossil collector, Pontoppidan knew that fossils recorded real organisms, somehow embedded in the rocks “as if they had been impressed into a paste, or dough….” But by what mechanism, exactly, could the Flood liquify and reset the rocks of the earth? Once set, what forces (perhaps “a universal earthquake, or the like”) could cause the “general confusion” of strata visibly raised, sunk, disjointed or even overturned?  And, while the Deluge might form simple hills and valleys, what of dense mountains which “seem to have been elevated from beneath, in a convex form, by a violent force of subterraneous wind, water, and fire, heaving them up and scattering them about in so many protuberances”?5

Pontoppidan the Skeptic

Over a century later, skeptical scientist Henry Lee's 1883 debunking book Sea Serpents Unmasked (correctly) criticized Pontoppidan for giving too much weight to eyewitness testimony about sea serpents — the very criticism skeptics (correctly) make of cryptozoology today. Yet, “if those who ridicule him had lived in his day and amongst his people,” Lee felt, “they would probably have done the same; for even Linnaeus was led to believe in the Kraken….”6

Overall, Lee argued, Pontoppidan's critical approach was worthy of praise.

The Norwegian Bishop was a conscientious and painstaking investigator, and the tone of his writings is neither that of an intentional deceiver nor of an incautious dupe. He diligently endeavoured to separate the truth from the cloud of error and fiction by which it was obscured….7

Pontoppidan thought of himself in just such skeptical terms. He invited criticism and factual corrections, saying,

…the discovery of truth, is in this and every other respect, my chief end, and I live in an age, which not content with mere hypotheses, unsupported by proofs, requires that every fact or position, which is advanced as real, be at least demonstrated possible, and consonant with the nature of things in question.8

Even more interesting, Pontoppidan made skeptical inquiry into popular claims an explicit goal for his Natural History of Norway.

I am very far from desiring to relate, or establish marvellous things, merely to excite the admiration of the reader. On the contrary, I have endeavoured to rectify the erroneous idea which many, even among the learned, have, for want of better information, formed of several, in themselves very wonderful natural phenomena, here in Norway; such as bottomless sea-abyss growing in the Moskoe-strom, penetrating quite thro’ the globe, of ducks growing on trees; of a water on Sundmoer, which in a short time turns wood into stone, and many other such things, which, some who have had no opportunity of enquiring further, or others who were not disposed to it, have received as undoubted facts.9

Tree Goose

Enter the Tree Geese

This brings us to Pontoppidan's skeptical investigation of a very odd piece of European folklore: the idea that some waterfowl literally grow out of trees or wood. It may sound ridiculous, but this legend persisted for centuries. It was well-established by 1187.11 In 1883 (a century after Pontoppidan) the legend remained current.12

Natural History of Norway quotes this description of the legend:

It is said that a particular sort of Geese is found in Nordland…which leave their seed on old trees, and stumps and blocks lying in the sea, and that from that seed there grows a shell fast to the tree, from which shell, as from an egg, by the heat of the sun, young Geese are hatched, and afterwards grow up, which gave rise to the fable, that Geese grow upon trees.13

(Because these geese were said to hatch from trees, incidentally, they had implications for religious dietary practice. In 1215, Pope Innocent III prohibited the enduring practice of eating tree or “barnacle” geese during Lent.14)

Though this folkloric belief was commonly “taken on the credit of one to another,” Pontoppidan wrote, “That any kind of fowls should grow upon trees, and be properly and truly called Tree Geese, is a thing which I have narrowly examined into, and find without the least foundation.”

His investigation revealed that the two parts of the legend were unconnected. On the one hand, the geese identified in the tale “generate in the common way,”  from eggs; on the other hand, the “barnacles” or “shells” identified in the legend (tree galls or bulbous growths) had nothing whatever to do with geese.

Pontoppidan dissected many of these galls, and discovered that they contained larval insects. Silky filaments within the galls had a feathery look, which presumably gave rise to the legend. Case closed — though like many skeptical investigations, this well-publicized scientific explanation failed to dispel the popular false belief.


What are we to make of all this? I draw several lessons. One is a renewed reminder to myself: always read original sources.

Another — and this is a theme I'll be returning to throughout this year — is a reminder that the world does not break down to spiral-eyed crazies on one side, and right-thinking skeptics baptized in critical thinking on the other. People are more complicated than that.

Pontoppidan promoted ideas we now know to be naive, but he was not a cartoon cut-out. He also conducted investigations, solved mysteries, and advocated for science literacy — in language that I as a modern skeptic find astonishingly familiar.

And yet… the guy did believe in mermaids.15

Further Reading

For a very thorough discussion of the legend of the Tree or Barnacle Goose, I recommend skeptic Henry Lee's chapter on the subject in his 1883 book Sea Fables Explained.


  1. Lyons, Sherrie Lynn. Species, Serpents, Spirits, and Skulls: Science in the Margins in the Victorian Age. (State University of New York Press: Albany, NY, 2009.) p. 22
  2. Pontoppidan, Erich. Natural History of Norway: In Two Parts. Part One. (Printed for A. Linde: London, 1755.) p. v. As reproduced by ECCO Print Editions. LaVergne, TN, USA. Jan 6, 2011.
  3. ibid. p. vii – viii
  4. ibid. p. v
  5. ibid. p. 56
  6. Lee, Henry. Sea Monsters Unmasked. (William Clowes and Sons: London, 1883.) p. 2 – 3
  7. ibid.
  8. Pontoppidan. Natural History of Norway: In Two Parts. Part One. p. xi
  9. ibid. p. x – xi
  10. Pontoppidan, Erich. Natural History of Norway: In Two Parts. Part Two. (Printed for A. Linde: London, 1755.) p. 52. As reproduced by ECCO Print Editions. LaVergne, TN, USA. Jan 6, 2011.
  11. Lee, Henry. Sea Fables Explained. (William Clowes and Sons: London, 1883.) p. 93. As reproduced by Kessinger Publishing. Jan 23, 2011.
  12. The Penny Magazine of the Society for the Diffusion of Useful Knowledge. “Economical Uses of the Oak.” (Charles Knight & Co.: London, 1843.) Volume 12. p. 304. As reproduced by Google Books. Retrieved Feb 8, 2011.
  13. Pontoppidan. Natural History of Norway: In Two Parts. Part Two.p. 52.
  14. Lee. Sea Fables Explained. p. 100
  15. In fairness, Pontoppidan was well aware that the majority of mermaid lore was unreliable, writing “The existence of this creature is questioned by many, nor is it at all to be wondered at, because most of the accounts we have had of it, are mixed with meer [sic] fables, and may be looked upon as idle tales.” Pontoppidan. Natural History of Norway: In Two Parts. Part Two. p. 186

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18 Responses to “Bishop Pontoppidan Versus the Tree Geese”

  1. I do think collars like the one Pontoppidan is wearing in the picture should come back into vogue.

  2. Thank you for this post. It is always good to be reminded that people are complex and do not easily fit into little boxes. I know it is tempting to stereotype those who disagree with us; sometimes, difficult to avoid.

    It also doesn’t hurt to look in the mirror sometimes and see that all of us can be susceptible to erroneous beliefs.

  3. arjun says:

    Unfortunately, rational people can hold irrational beliefs. It seems most of these beliefs. like the tree geese, originate from casual observation followed by faulty analysis leading to an irrational conclusion. When i first started shaving i, and many of my friends, believed that the more you shaved, the thicker your beard would grow in, so i tried to avoid shaving. Obviously, a guy’s beard grows in thicker and thicker as he passes between childhood and adulthood, having nothing to do with how often he shaves. But i still meet adults who believe this one.

  4. jackd says:

    Anyone who wants to do any further digging, even if it’s just a quick Google search, should be sure to look for “barnacle geese”. At least that’s the term I was familiar with before this article.

    • Max says:

      Yeah, that’s the old theory of spontaneous generation that Creationists like to confuse with the modern theories of abiogenesis.

  5. Trimegistus says:

    An excellent little piece of science history. Well done.

  6. Robo Sapien says:

    One of my biggest pet peeves is when people say the old adage “there are two kinds of people in this world…” and fill in the blank with their own half-assed simplification of human existence.

    This gives me a nice analogy to use when I slap them upside the head. Thanks Daniel.

    • LovleAnjel says:

      There are two kinds of people in this world…those that divide everything into two categories and those that don’t.

      • Robo Sapien says:

        Within those two categories, there are two more categories – those who give a damn and those who don’t – making a total of four kinds of people. But then you also have people who see the glass as half empty and those who take the half full position, so that makes eight. Oh, and let’s not forget about those who believe in Chopra’s observer theory, and those who are certain that bears really do shit in the woods even if there is noone around to smell it. So now we’re up to 16…

      • Mathmaniac says:

        Actually, there are three kinds of people in the world: those who can count and those who can’t.

  7. Loren Coleman says:

    While I would hardly say that I “believe” in Mermaids and Mermen, well, let’s say I accept the possibility there is something to the stories and folklore behind Merbeings. Of course, that “something” might merely be that they are seals, sea lions, sea cows, dugongs, and manatees.

    Cryptozoologists, after all, are not stupid, and most are more skeptical than we are given credit for being.

    • Cryptozoologists, after all, are not stupid, and most are more skeptical than we are given credit for being.

      Indeed, that is a theme I return to quite often. Pontoppidan is an illustrative example of a writer with a place in both cryptozoological history and skeptical history — and he would have considered these contributions to be indistinguishable.

      Pontoppidan brought his critical faculties to bear even on the topic of mermaids, writing,

      The existence of this creature is questioned by many, nor is it at all to be wondered at, because most of the accounts we have had of it, are mixed with meer [sic] fables, and may be looked upon as idle tales.

  8. Is it really that credulous for Pontoppidan (1698 – 1764) to believe in mermaids in the 1700’s? The ocean is a mysterious place and there were far fewer reliable studies of sea life back then. Hybrid creatures seem ridiculous today only the light of more than 200 years of additional biology research. We’ve got genetics, evolution and a much more detailed understanding of what is plausible and implausible.

    Also, as Loren pointed out, misunderstood marine mammals may account for some of the tales of mermaids. Skeptics know better than most the myriad ways one’s mind can be tricked – and even thus forewarned are susceptible to the same mistakes, errors and fallacies.

    Your point is well made, and worth remembering. Of course, another facet of oversimplification is ignoring evidence contrary to one’s viewpoint. For example, those who wish to deify our founding fathers often gloss over their mistakes, their bigotry, their ignorance, etc… Thomas Jefferson was a very clever man, for example, but he kept slaves. (And thought it likely that herds of mammoths roamed the interior of North America.) It is just so difficult to judge the beliefs of others in the context of the limitations of their time – and through our modern eyes and sensibilities every previous age seems barbaric. And in the future, no doubt, so shall we be seen.

    • DoctorAtlantis asks,

      Is it really that credulous for Pontoppidan (1698 – 1764) to believe in mermaids in the 1700′s? The ocean is a mysterious place and there were far fewer reliable studies of sea life back then.

      This point is well-taken. As well, it is not the case that Pontoppidan viewed the topic uncritically. I’ve added an endnote with a relevant quote.

      I may return to Pontoppidan in another post soon. He makes a sophisticated argument for eyewitness testimony in regard to mermaids, which is well worth a deeper look:

      One might as well doubt whether there be Hottentots, for tho’ the number of witnesses be much greater in that case, still that does not alter the nature of the knowledge, it only raises it to a higher degree of certainty.

  9. Heliocles says:

    Very interesting article! One small point, though:

    Actually, ““great Sea snake, of several hundred feet long” likely refers to a fully historical creature, though its appearance has been somewhat distorted. This should be a reference to the Nemertea (ribbon worm) Lineus longissimus or bootlace worm, where known specimens have been as long as 180 feet, even though the girth is at most a few centimeters.

    The great sea snake is present on maps of the North Sea from as early as the 16th century, though it does of course look little like a real snake (and even less than a dragon), as it has sometimes been depicted.

  10. Malachi Constant says:

    Great post, I’m really fascinated by the the people involved around the time of the birth of modern science. I’m reading “The Sceptical Chymist” by Robert Boyle right now. This was written at a time when many “natural philosophers” still thought that you could learn chemistry just by reason alone — no need to actually do a whole bunch of experiments! Many still believed that earth, air, fire, and water were the four Elements, the only competing theory was that they were Mercury, Sulfur, and salt!

    The book is hilarious, because despite his flowery language he’s basically saying, “Look, guys, you can’t just make up any airy-fairy nonsense just because it sounds good. Define your terms as concretely as possible and for god’s sake test them. Then tell us exactly what you did an we’ll see if we can do it too.”

    To modern eyes he’s amazing patient and goes to great lengths to explain why using scientific method is how everyone should be doing things.

    By the way, the guys actually doing experiments were called “vulgar spagyrists”. I’m gonna see if I can get that printed on my degree when I graduate.

    P.S. Daniel, I gave your book on Evolution to my niece for christmas and she loves it. She’s obsessed with animals right now, so I glad you I had your book to give to her. One more Texan has been presented with the ToE thanks to you.