The Sacred Sacred Ibis

The ancient Greeks usually depicted Thoth—their god of writing, wisdom and magic—as having the head of a bird with a long, down-curving bill.  Until the 1800s, Europeans thought that this bird was probably a curlew, a stork or a heron. Linnaeus believed that the bird must be the Cattle Egret which he called Ardea ibis in the 1758 edition of his Systema Naturae. It was not until the turn of the 19th century that a small group of French scientists and naturalists finally confirmed the connection between Thoth and the head of the African Sacred Ibis (Threskiornis aethiopicus). This species was not unambiguously described until 1790 [1], but it took Napoleon Bonaparte’s military campaign to Egypt to provide the connection between this species and Thoth.

We now know that the sacred ibis was considered (and revered) by the Egyptians to be the earthly form of Thoth. For about a millennium starting in 1100 BC, ibises were frequently mummified as an offering to Thoth, believing that mummification would put the birds on a direct line to the afterlife. As a result, several million sacred ibises were killed, gutted, embalmed and folded with the bill tucked between the tail feathers. The carcasses were then wrapped with linen dipped in resin, and inserted individually or in pairs into urns that were placed in vast underground caverns in cities all along the Nile. Many of these mummified ibises have grains, snakes, snails and other foods in their body cavities, possibly to provide the birds with some food in the afterlife.

But why ibises, and where did all of these birds come from? There can be no doubt that the sacred ibis was a reasonably common bird [2] in swampy areas all along the Nile in the Late and Ptolomeic Periods of ancient Egyptian civilization [3]. Those birds were of great value to nearby villages as they ate the snails that infested fish ponds, snails that harboured parasites dangerous to humans. They were also claimed to feed on flying snakes (?) and generally consumed all kinds of human refuse [4]. No wonder they were considered to be sacred.

At several sites of ancient cities along the Nile, archaeologists have found incredible numbers of mummified ibises: 1.75 million at Saqqara, 4 million at Tuna el-Gebel, for example. Even over a period of 500 years that is a lot of birds per year, likely magnitudes more than could have been hunted in the local marshes for any sustained period. Because of their religious importance, sanctuaries dedicated to the ibis sprang up all over the country, where birds were bred and raised in captivity, processing as many as 20,000 ibises per year for the votive ibis industry. Priests apparently gathered eggs for artificial incubation and tended the large flocks, as well as engaging in a large pottery industry to make urns for the mummified birds. These ibiotropheia may well be the earliest examples of bird-farming that did not involve some form of fowl.

The vast stores of ibis mummies in Egypt were brought to light by Geoffery Saint-Hilaire and Jules-César Savigny, two of the 167 savants [5] who accompanied Napoleon Bonaparte to Egypt from 1798-1801. Savigny noticed that the ibis often appeared in hieroglyphics and tomb paintings, and reasoned that this bird was important to Egyptian culture. He wrote up his discoveries in 1805 as Histoire naturelle et mythologique de l’ibis which included some very nice illustrations.

Georges Cuvier, one of the leading French biologists of the day, was asked by Napoleon to join the Egyptian contingent, but he suggested that Savigny go instead, so he could continue his work on molluscs. But it was Cuvier who first measured two mummified birds brought back from Egypt by Col. Jacques François-Louis Grobert [6] from the catacombs at Saqqara.  Cuvier initially concluded that those birds were probably curlews as they were smaller than some contemporary ibis specimens [7]. He later measured two mummies that Geoffrey Saint-Hilaire had brought home from Thebes. Those measurements plus the colours of some intact feathers convinced him that the mummies collected by Saint-Hilaire were indeed sacred ibises, and his 1804 paper has a very nice summary of his reasoning and all of the previous mis-identifications. Cuvier’s assistant even pieced together the bones from different mummies to make a complete skeleton (see picture below).

Even though the ibis mummies from Saint-Hilaire were not exactly the same size as contemporary birds, Cuvier also used those measurements to bolster his arguments of the fixity of species—evidence that species were created once by a deity and did not change through time. This argument put him at odds with his colleague Lamarck who argued that species changed through geological time.

I was made aware of this ibis story in a new essay in PLoS Biology [8], by Caitlin Curtis, Craig Millar and David Lambert. As Jerry Coyne noted in an essay on his Why Evolution is True site, not many evolutionary biologists seem to be aware of this as an early test of evolutionary change. The reason, I think, is that it was not actually a test [9]. The story is actually rather well known and has been published many times in scientific journals and the popular press ever since Cuvier’s initial publications [10]. While the new essay summarizes many aspects of this story the authors present no evidence in support of some of their claims and I am not entirely convinced by some of their assertions.

When interpreting the past here is always a danger of applying present knowledge and values incorrectly. In this case, I cannot yet tell if my different interpretation of this interesting story is correct. I will need to read the work of Cuvier, Lamarck, Saint-Hilaire and Savigny in the original French and Latin to put the whole story in context but that will take a while, even though all of the relevant texts are now available online. I will revisit the topic when I have done the necessary research.

Whether the details in this new essay by Curtis and colleagues are correctly interpreted or not, it does end with a curious conclusion that I feel deserves some further discussion: Of great importance is the reminder, even today, of the power of a strong personality and that the belief in “what they know to be true” can dramatically influence the direction of science and public opinion. I do not think that anyone would dispute that strong personalities and beliefs can influence science and public opinion. Take, for example, Julian Huxley’s rejection of Darwin’s ideas on sexual selection [11], undoubtedly reducing interest in that topic for the next 50 years or so.  And while it is true that Huxley and Cuvier had strong personalities, and were great communicators and relatively powerful men, I think that their arguments held sway largely because they made them clearly and because there was neither compelling evidence nor any clear and logical mechanisms to explain the existing patterns. In both cases the delays in the progress of science were reasonably short and probably needed the ideas and considerable evidence presented by Darwin and Wallace, and Williams and Trivers, respectively, before there could be any real progress.

Finally, it has probably not escaped your notice that the African Sacred Ibis has been depicted on the cover of The Ibis in one form or another ever since 1859. This may seem a bit odd as that bird does not occur in the wild in Britain and only sparsely in southern Europe through introductions. Thus the sacred ibis does not really appear to be a fitting symbol for the British Ornithologists’ Union. There is a long and interesting story there, but that too will have to wait for another day.

SOURCES

• Birkhead TR, Wimpenny J, Montgomerie R (2014) Ten Thousand Birds: Ornithology since Darwin. Princeton, NJ: Princeton University Press.
• Cuvier G (1804) Mémoire sur l’ibis des anciens Égyptiens. Annales du Muséum d’histoire naturelle 4:116-135. [available here]
• Cuvier G (1812) Recherches sur les Ossemens Fossiles de Quadrupèdes : où l’on rétablit les caractères de plusieurs espèces d’animaux que les révolutions du globe paroissent avoir détruites, t1-4. [Studies of the Fossil Bones of Quadrupeds, volumes 1-4] Paris: Deterville. [available here]
• Cuvier G (1826) Discours sur les révolutions de la surface du globe, et sur les changemens qu’elles ont produits dans le régne animal. Paris: G. Dufour. [available here and in English translation of the 1825 edition here]
• Lacépède B-G-E, Cuvier G, Lamarck J-B (1802) Rapport des professeurs du Muséum sur les collections d’histoire naturelle rapportées d’Égypte, par E. Geoffrey. Annales du Museum d’Histoire Naturelle 1: 234–241. [available here]
• Latham J (1790). Index Ornithologicus, Sive Systema Ornithologiae: Complectens Avium Divisionem In Classes, Ordines, Genera, Species, Ipsarumque Varietates (2 Volumes, in Latin). London: Leigh & Sotheby. [available here]
• Le-Suer RB, ed (2012) Between Heaven and Earth: Birds in Ancient Egypt. Chicago: The Oriental Institute of the University of Chicago
• Linnæus  C (1758) Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis, 10th edition.  Stockholm: Laurentius Salvius.
• Rosser WH (1837) Mummy of Egyptian Ibis. The Gentleman’s Magazine 6 (new series): 145-148. [available here]
• Savigny J-C (1805) Histoire naturelle et mythologique de l’ibis [Natural and Mythological History of the Ibis]. Paris: Allais. [available here]

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Footnotes

1. ibis described: see Latham 1790 page 706 where he calls it Tantalus aethyopius
2. Sacred ibis once common in Egypt: but it is no longer found in that country, disappearing as the swamps and marshes were drained to provide land for the increasing population and agriculture.
3. Late and Ptolomeic Periods: about 700 BC until 30 BC ending with the death of Cleopatra and the conquest of Egypt by the Romans
4. ibises eating refuse: in Australia, where they have been introduced, they are often called ‘bin chickens’ as they are often seen foraging in trash cans in city parks. In the park beside the Australian National Museum in Sydney, I once watched a very dirty-looking ibis sneak up behind some picnickers then reach over the shoulder of a little boy to snatch his sandwich out of his hand. Clearly, their bills are adapted for sandwich snatching (!), and they are fearless.
5. savants: these were scholars and scientists. The Journal des Sçavants (later called Journal des Savants) began publishing in January 1665, a couple of months before the Philosophical Transacations of the Royal Society, considered (erroneously) by many to be the first scientific journal. Frankly, I don’t see that it matters who was first, or even if it was one of those two.
6. Grobert: (1757-181?) was a French artillery officer who wrote about the pyramids etc. on his return from the Egyptian campaign. See Cuvier (1826), which updates some of the information in his 1804 publication about his later study of some different mummies.
7. smaller than contemporary ibises: On examining four more ibis mummies, Cuvier recognized that one of them was a juvenile based on its bone structure (Cuvier 1826). As a result, he realized that they may not be curlews at all but simply smaller, juvenile ibises. This is not so surprising as it turns out the many of the ibis mummies were clearly made from juvenile birds. No doubt the priest-farmers who raised the ibises for the votive market saw no reason to keep the birds any longer than was needed to make them suitable for mummification.  That just made good economic sense to maximize their profits.
8. article in PLoS Biology: unlike the scientific articles in that journal, this one is labelled ‘Essay’ which they say “are opinionated articles on a topic of interest to scientists, as well as to a broader audience, including the general public”. Opinions are fine but I am surprised at the absence of clear evidence in support of the claims made.
9. not actually a test: Cuvier simply used his measurements identifying the mummies as sacred ibises to suggest that there had not been much change in their morphology in the past 3000 years. But the ibis was just one of many examples that he referred to. Moreover, as Coyne noted, this was at best a ‘one-way test’ as any lack of change would be consistent with slow evolutionary change. Cuvier even acknowledged that the the measurements were not the same between the mummies and contemporary ibises. I don’t see this as a test of any kind because Cuvier was unlikely to be convinced by any such results: if the mummies were the same as extant ibises, then no change; if they were different then they must be different species.
10. the story of Cuvier’s ibis measurements: in a quick search on the internet, I found more than 20 articles on Cuvier’s ibis measurements dating back to Rosser (1837)
11. Huxley and sexual selection: see Birkhead et al. (2014)