Fossils and Extinction
When we think of fossils, we usually think of extinct life embedded in rock. Chances are, the rock is part of an outcrop exposed by erosion and free of vegetation. It's hard and obviously old; we casually think it must be millions of years old, It's also clear that the animal or plant embedded within it must be long-gone.
The reality for collectors during Jefferson's time and place was quite different. A great many of the bones and teeth of the "animal de l'Ohio, "American incognitum" or "Mammoth" (American mastodon) from Big Bone Lick (1), were found lying on the ground. Those belonging to Peale's "Mammoth", also an American mastodon, were discovered by workmen digging in soft mud. The bones of the Megalonyx were found by other workmen collecting saltpeter (2) covering a cave floor. There was no compelling reason to believe the remains belonged on extinct animals, or that they were of great age.
Jefferson and his collectors also had dramatically different worldviews than ours. There was nothing in their education or personal experiences to dispel the perception that Nature changed substantially since its creation a few thousand years ago. A Christian interpretation of Genesis molded the worldview of most Europeans and their descendants in the New World. Deism, a theology born of the European Enlightenment (3), shaped the worldview of Jefferson and several of his closest associates.
Most Christian and Deist thinkers of the 18th century held that the world and all living things were the result of a perfect creation by a divine being. They embraced the scala naturae, or "Great Chain of Being", as the grand organizing principle of the Creation. This concept had its roots with the teachings of Aristotle, and reached what is arguably its best Enlightenment expression with the German philosopher/naturalists Gottfried Wilhelm Leibniz (1646-1717).
The Great Chain of Being was an unbroken progression from the lowliest—or least perfect— matter to the highest —or most perfect— being(s); Diests commonly held that humans were the most perfect creation, but Christians typically ranked them below angles and God. The criteria for ranking along this chain varied among philosophers, as did the actual rankings, but they roughly corresponded to our conception of complexity. A typical progression would contain the simplest "elements" (e.g., water) followed by minerals, mushrooms, green plants, jellyfish, worms, insects, serpents, fishes, birds, cow, monkeys and humans. Leibniz and other Enlightenment thinkers believed the chain was perfect and unbroken. Indeed, 18th century naturalists spent considerable effort in searching for "missing links" (i.e., intermediate forms) and in reorganizing known forms to better fit the continuum.
An important aspect in Leibniz's conception of the Great Chain of Being was plenitude. An all powerful and capable God would surely have created all that was possible to create; gaps in the chain would thusly have been unthinkable. Moreover, God's benevolence would have precluded the extinction of any part of Creation; gaps in the chain would be unacceptable.
Thomas Jefferson and several of his associates at the American Philosophical Society in Philadelphia believed in the Chain of Being and embraced the idea of plenitude. They also held that nature was inherently frugal. This "economy of nature" meant that nature would not be wasteful of her creations. In arguing for the continued existence of the "Mammoth" (American mastodon) in his Notes on the State of Virginia Jefferson wrote:
"Such is the economy of nature that no instance can be produced, of her having permitted any one race of her animals to become extinct; of her having formed any link in her great work so weak as to be broken."
Another concept that united most Christians and Diests was the "Balance of Nature". As with the Chain of Being, this concept had its origins among the Ancient Greeks. The interactions of animals, plants and the physical environment were harmonious; any imbalance was temporary and would quickly be remedied. Extinction in such a context would be extremely unlikely. For instance, despite being repeatedly preyed upon by cougars, deer continue to reproduce and thrive. Moreover, the possibility of extinction suggested a catastrophic flaw in the Grand Design. Given a single creation, if one species could become extinct, what —over time— would prevent the loss of all. In his argument for the continued existence of the Megalonyx (4) Jefferson stated:
"The movements of nature are in a never ending circle. The animal species which has once been put into a train of motion, is still probably moving in that train. For if one link in nature's chain might be lost, another and another might be lost, till this whole system of things should be evanish by piece-meal; a conclusion not warranted by the local disappearance of one or two species of animals, and opposed by the thousands and thousands of instances of the renovating power constantly exercised by nature for the reproduction of all her subjects, animal, vegetable, and mineral."
Despite these powerful arguments against extinction, evidence for the disappearance of species slowly accumulated. The most powerful evidence came from fossils.
People had long been familiar with fossils, but had differing ideas about their identity and significance. Even the word fossil had a meaning different from our own. It comes from the Latin word fossilis , which simply means, "dug up" or "from the earth."
Some of the Ancient Greeks held that the fossils of marine fishes and intertebrates they encountered were the result of strandings that followed changes in sea level. Centuries later, many European scholars contended that fossils were lusus naturae (sports or accidents of nature) that were spontaneously created within the rock. This might be due to Nature's ability form any variety of shapes in rocks as is evident with crystals. Alternately, some proposed the widespread occurrence of "germs" (seeds of life) that spontaneously generated into life or —if trapped within rocks— into fossils.
The competing idea was that fossils were the remains of once living organisms. In 1666, Nicholas Steno (1638-1686) concluded that the familiar glossopterae (tongue stones) were in fact fossilized shark teeth (5). Some of Steno's contemporaries, including Robert Hooke (1635-1703) and John Ray (1628-1705), also argued for the organic origin of fossils. However, the idea of lusus naturae remained popular. After all, how could one explain the mineral nature of fossils if they were once the remains of living beings? Moreover, how could you explain the presence of fossils on mountaintops? (6)
Nonetheless, the contention that fossils were the relicts of former life gained increasing acceptance during the 18th century. Acceptance was particularly widespread among practitioners of natural theology (Christian scholars who studied Nature to elucidate God's work). They contended that fossils were the victims of the universal, Biblical Flood. The supernatural scale of this event was used to explain the presence of marine fossils on mountaintops. It was also used to explain how the remains of tropical "elephants" (mammoths) could be found in Siberia (7). More significant in the long run, however, was that invoking the Flood made the idea of extinction widely acceptable.
The biggest problem with this explanation, however, was that fossils were often found in distinct strata (geologic layers). This singular and supernatural event might explain fossils if they were limited to a single stratum, but not to several of them. The multiple occurrence of fossil-rich strata within the geologic column confounded some naturalists, including Robert Hooke and John Ray, but it wasn't until the last years of the 18th century and the first decades of the 19th that the central role of the Biblical Flood was seriously challenged.
Beginning in the 1790s, William Smith (1769-1839) documented strata and their associated fossils throughout much of Great Britain. He soon realized that many fossils were limited to particular strata and that these sequences of strata and their respective fossils were often consistent from place to place. This led Smith to develop his principle of faunal succession in which he used fossils to identify particular strata among geologic exposures, even when they were many kilometers apart. The principle was so robust that Smith used it to construct a comprehensive geologic map of England, Wales and southern Scotland that was finally published in 1815.
Meanwhile, Georges Cuvier (1769-1832) and Alexandre Broginart (1770-1840) conducted a systematic geological and paleontological study of the Paris Basin. In preliminary (1808) and subsequent publications, including Cuvier's Ossemens fossiles (1812), they documented the existence of two distinct terrestrial faunas that were predictably separated by many meters of marine sediments. Moreover, the species found in the deeper —and older— of the two strata were unlike any modern mammals. On the other hand, those from the other, younger stratum were similar to but still distinct from modern species (8).
Even before the demonstration of fossil succession, some naturalists and scientists supported the idea of extinction independent of the Biblical Flood. For instance, Buffon wrote in his 1749 essay "Théorie de la terre" (Theory of the Earth) that the large ammonites and belemnites (9), —known only from fossils— must have died out long ago. However, many of his contemporaries held that it was impossible to know whether they were truly extinct because so much of the ocean was inaccessible to humans.
This last argument was much harder to sustain in the case of the large terrestrial quadrupeds (four-legged vertebrates); large quadrupeds presumably have a harder time remaining concealed. In 1768, for instance, the British anatomist William Hunter (1781-1783) concluded that the American incognitum (American mastodon) was almost certainly extinct. But it wasn't until a few decades later that the idea gained widespread acceptance. It did so primarily through the efforts of one man, Georges Cuvier.
Cuvier was a master of comparative anatomy, theoretical biology and persuasion. In 1796 he convincingly demonstrated that the Siberian mammoth and the "animal de l'Ohio" (American mastodon) were separate species both from each other and from modern elephants; he also demonstrated that modern African and Indian elephants were in fact two separate species. Moreover, Cuvier successfully argued the mammoth and mastodon, as well as a host of other quadrupeds, were extinct:
"What has become of these two enormous animals of which one no longer finds any [living] traces, and so many others of which the remains are found everywhere on earth and of which perhaps none still exist? The fossil rhinoceros of Siberia are very different from all know rhinoceros. It is the same with the alleged fossil bears of Ansbach; the fossil crocodile of Maastricht; the species of deer from the same locality; the twelve-foot long animal, with no incisor teeth and with clawed digits, of which the skeleton has just been found in Paraguay: none has any living analogue (10)."
Through his work at the Paris Basin and his analysis of fossil quadrupeds collected from North and South America, Europe and Siberia, Cuvier convinced the majority of European naturalists that extinction was a reality. On the other hand, Thomas Jefferson still resisted the idea, although he now acknowledged the possibility of extinction. It's not clear how well informed Jefferson was of Cuvier's arguments for extinction during the first years of the 19th century. We know he was somewhat aware of Cuvier's work on the giant ground sloth (Megatherium) from Paraguay in 1797 (11), but he was not yet convinced that the either Megalonyx or the "mammoth" (mastodon) was extinct.
Thomas Jefferson's resistance to the idea of extinction was probably still influenced by his Deism and his belief in the Perfection of Creation. But his opposition was also influenced by his geographic perspective. As a European, Cuvier was comfortable with the idea that if no one had seen an animal, it must no longer be around. But unlike Europe, which had been thoroughly explored, most of North America was still unknown. Jefferson—arguably the person most knowledgeable about the natural history and geography of North America—was acutely aware of the limits of what was known. In 1797, for instance, he stated: "Our entire ignorance of the immense country to the West and North-West, and of its contents, does not authorise us so say what it does not contain."
In 1803 President Jefferson instructed Meriwether Lewis to search for these animals before he and William Clark set off to explore the Louisiana Purchase and seek a navigable passage to the Pacific (12). They never found these animals, and it's not clear whether Jefferson now accepted the extinction of these giant quadrupeds, but apparently accepted it years later. (13) In andy case, he clearly felt that excavating their fossils was still a useful endeavor. In 1807, he enlisted Clark to recover "mammoth" bones from Big Bone Lick. Kentucky. Some of fossils collected by Clark were sent to the museum in Paris where Cuvier conducted his studies of extinct animals, and some were prominently displayed in the entryway of his home at Monticello (14).
Back in France, Cuvier grappled with the implications of the extinctions he so convincingly demonstrated. He regarded the quadrupeds he studied as immutable machines well suited to their environment. So what extraordinary events rendered them extinct? The faunal successions and abrupt geologic transitions he saw in the rock formations near Paris and elsewhere convinced Cuvier that they succumbed to catastrophic "revolutions." (See Cuvier's Revolutions of the Globe for more information.)
Variations of Cuvier's catastrophism, in which either extraordinary natural processes or Divine intervention caused the extinctions, would influence European and American thinking throughout much of the 19th century. Alternatively, the French scientists Lamarck circumvented the extinction question by proposing the mutability of species. To him species transformed (i.e., evolved) from one form into another, and the extinctions perceived by others were actually misinterpretation of the fossil and geologic records (15).
A dramatically new approach to extinction appeared with the publication of Charles Darwin's On the Origin of Species in 1859. Darwin proposed that extinction was a normal feature of Nature. It occurred all the time; he considered the apparently sudden disappearances and appearances of species to be artifacts of an imperfect fossil record. Moreover, extinction was an essential contributor to the formation of new species. Living populations were inherently variable. The action of Natural Selection on this variability resulted in the extinction of some (unfit) forms and the continued survival and enhanced reproduction of others (16).
Websites:
- BBC's web page on Mass Extinction:
www.bbc.co.uk/education/darwin/exfiles/massintro.htm - Talk.Origin's web page on Punctuated Equilibrium:
www.talkorigins.org/faqs/punc-eq.html - UC Berkeley Evolution Websites' pages on …
Geoges Cuvier and Extinction:
evolution.berkeley.edu/evosite/history/extinction.shtml
Robert Hooke and Fossils:
www.ucmp.berkeley.edu/history/hooke.html
John Ray and Fossils:
www.ucmp.berkeley.edu/history/ray.html
William Smith and Biostratigraphy:
evolution.berkeley.edu/evosite/history/biostratigraphy.shtml
Nicolas Steno, Fossils and Stratigraphy:
evolution.berkeley.edu/evosite/history/fossils.shtml
Print Resources:
- Boorstin, Daniel J. 1993. The Lost World of Thomas Jefferson. Chicago: University of Chicago Press.
- Buffon, Georges Louis LeClerc, comte de. 1749-1788. Histoire naturelle, générale et particulière. Paris: Imprimeries royale.
- Carey, S.W. 1988. Theories of the Earth and Universe: A History of Dogma in the Earth Sciences. Stanford: Stanford University Press.
- Cohen, C. 2002. The Fate of the Mammoth: Fossils, Myths and History. Translated by William Rodarmor. Chicago: University of Chicago Press. Originally published as Le Destin du Mammouth. 1994. Paris: Editions du Seuil.
- Cuvier, Geoges. 1796. "Notice sur le squelette d'une très-grande espèce de quadrupède onconnue jusqu'à présent, trouvé au Paraguay, et déposé au cabinet d'historie naturelle de Madrid, redigée par G. Cuvier". Magasin encyclopédique, 2e anée, 1: 303-310.
- Cuvier, Georges. 1796. "Mémoire sur les épèces d'elephants tant vivantes que fossils, lu à la séance publique de l'Institut National le 15 germinal, an IV." Magasin encyclopédique, 2e anée, 3: 440-445.
- Cuvier, Georges. 1806. "Sur le grande Mastodonte, animal très-voisin de l'éléphant, mais à mâchelières hérissées de gros tubercles, dont on trouve les os en divers endroits des deux continens, et surtout près des ords de l'Ohio, dans l'Amérique Septentrionale improprement nommé Mammouth par les Anglais et par les habitans des États-Unis." Annales du Muséum d'Histoire Naturelle 8:270-312, pls 49-56.
- Cuvier, Georges. 1812. Researches sur les ossemens fossiles de quadrupèdes, òu l'on rétablit les caractères de plusieurs espèces d'animaux que les révolutions du globe paroissent avoir détruites. 4 vol. Paris: Deterville.
- Cuvier, Georges, and Alexandre Brongiart. 1808. "Essai sur la géographie minéralogique des environs du Paris". Annales du Muséum d'Historie Naturelle 11: 293-326.
- Cuvier, Georges, and Alexandre Brongiart. 1811. "Essai sur la géographie minéralogique des environs de Paris (lu 11 avrl 1808)". Mémoires de la Classe des Sciences mathématiques st physiqus de l'Institut Impérial de France 1810: 1-278.
- Mayr, E. 1982. The Growth of Biological Thought: Diversity, Evolution, and Inheritance. Cambridge, London: Harvard University Press.
- Miller, C.A. 1988. Jefferson and Nature: An Interpretation. Baltimore and London: John Hopkins University Press.
- Osborn, Henry Fairfield. 1935. "Thomas Jefferson as a Paleontologist" Science 82(2136): 533-538.
- Rudwick, M.J.S. 1997. Georges Cuvier, Fossil Bones and Geological Catastrophes: new translations. Chicago: University of Chicago Press.
- Semonin, P. 2002. American Monster: How the nation's first prehistoric creature became a symbol of national identity. New York & London: New York University Press.
- Winchester, S. 2001. The Map that Changed the World: William Smith and the Birth of Modern Geology. New York: HarperCollins Publishers.
Notes:
- Big Bone Lick is a famous fossil locality located near the Ohio River in Kentucky. See Big Bone Lick for more information. [go back]
- Saltpeter (potassium nitrate) is a mineral long used for a variety of purposes. For example, it's used in the manufacture of gunpowder, in the preservation of meats, and as fertilizer. Saltpeter deposits in caves were the result of extended accumulations of bat droppings. [go back]
- The Enlightenment was a period of intellectual upheaval and innovation in Western Europe and the early United States. Significant components of the Enlightenment emerged during the 15th and 16th centuries, but it reached its peak during the second half of the 18th century. Deism was a theology or philosophy that posited a supreme and divine intelligence that created the world. But, unlike Christianity (or other monotheist religions), the Diest God was remote from and indifferent to humans. Instead, after the World was created, it operated on a set of divinely ordained and immutable laws. The discovery of these laws was the goal of Enlightenment inquiry. See Thomas Jefferson, Product of the Enlightenment for more information. [go back]
- The Megalonyx (Great Claw) was a fossil limb from a West Virginia cave that had three large claws. In 1797, Jefferson gave a talk to the American Philosophical Society in which he presented the fossil and his interpretation of it. He concluded that it belonged to a rare species of giant cat that still roamed the wilderness. See Discovering the Great Claw: Part 1 - Jefferson's Giant Cat for more information. (back]
- Nicholas Steno, a Dane by birth, spent much of his life in Florence, Italy. In addition to his work with fossils, Steno developed two crucial principles that laid the conceptual foundations for the science of geology. The first was his "Principle of Original Horizontality", which held that layers (or strata) of sedimentary rock were originally deposited horizontally; subsequent processes may upturn, fold or otherwise distort these strata. The second principle was Steno's "Law of Superposition". Strata lower in the geologic column were laid down earlier than the strata above them. Consequently, they are older than the higher, superimposed (and younger) strata. [go back]
- The French philosopher Voltaire (1694-1778) was an influential proponent of the non-biological or inorganic origin of fossils. Thomas Jefferson initially favored Voltaire's argument in a section of his Notes on the State of Virginia concerning mountaintop fossils. Critical comments by some of his associates, however, convinced Jefferson to discard Voltaire's views in favor of a neutral position on the origin of these fossils. See A Sampling of Notes for more information. [go back]
- The first scientific studies of fossils Siberian (woolly) mammoths were based on isolated tusks, molars and teeth. Based on this limited information, naturalists reasonably concluded that the mammoth was actually an elephant. However, the presence of a tropical animal in northern Siberia presented an obvious problem: how did it get there. One popular idea was that their carcasses were transported from tropical localities to the Far North during the Biblical Flood. See About the Woolly Mammoth for more information. [go back]
- The younger of the two Paris Basin strata studied by Cuvier and Broginart is now recognized to be Pleistocene in age (less than 2 million years old). The older layer dates back to the Eocene; age estimates for the Eocene vary somewhat but generally range 54 to 38 million years ago. [go back]
- Ammonites and belemnites are chamber-shelled cephalopods (relatives of the octopus and squid) that are conspicuous and well represented members of Late Paleozoic and Mesozoic marine fossil assemblages. They died out completely at the end of the Cretaceous. [go back]
- This translation is from Rudwick (1997). In it, Cuvier refers to several recently discovered quadrupeds. The Siberian rhinoceros is now known as the woolly rhinoceros (Coelodonta antiquitatis), the Ansbach bears as cave bears (Ursus spelaeus), and the crocodile as a mosasaur (Mosasaurus). The "deer" refers to a supposed antler. Cuvier hadn't yet to examined this fossil, but when he later did so, he correctly identified it as part of a giant marine turtle's shell. The giant animal from Paraguay was identified by Cuvier as a relative of the sloth. He named it Megatherium. [go back]
- Cuvier published his paper on Megatherium in 1796. Jefferson learned of it the following year when he came upon a short account in a British magazine. (See Discovering the Giant Claw: Part 2 - the Ground Sloth for more information.) The next reliable account of Jefferson's familiarity with Cuvier's work is from November 1808, when he received Cuvier's correspondence thanking the president for the gift of fossils from Big Bone Lick. In April 1809, Jefferson received a letter from Charles Willson Peale concerning Cuvier's 1806 identification of the "mammoth" as the mastodon. (See Discovering the Mastodon: Part 9- Meanwhile, in Europe for more information.)
Circumstantial evidence suggests that although Jefferson and his countryman were aware of Cuvier and his importance to French science, they probably didn't know much about his actual work. Most of his publications were in French journals. An annotated translation of his Discours préliminaire (Preliminary Discourse) was published in England in 1813, but it wasn't until 1819 than an American edition was made available. Moreover, Cuvier's celebrated methods in paleontology and comparative anatomy were not widely known in the United States until they were popularized by Richard Harlan in the 1820s and 1830s. See Philadelphia School of Paleontology for more information. [go back] - Jefferson's written instructions to Meriwether Lewis stressed that in addition to the main tasks of exploring the Louisiana Purchase and seeking a navigable route to the Pacific, the expedition should investigate the natural history of the region. This included " the remains & accounts of any [animals] which may be deemed rare or extinct;". Although the reference is oblique, historians generally agree that Jefferson was referring to both the "Mammoth" and Megalonyx. More explicitly, Jefferson wrote in 1803 to the French naturalist Benard Lacépède concerning the expedition: "It is not improbable that this voyage of discovery will procure further information of the Mammoth, & of the Megatherium [Megalonyx]." [go back]
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Deism holds that the universe was the result of Divine Creation, but afterwards, its operation is determined by divinely authored universal laws. In other words, it runs in accordance with these laws and not through Divine intervention.
Sometime after he left the Presidency, Jefferson accepted the idea of extinction. He still held onto the idea of the Divine Creator and the Perfection of Creation, but now he felt the need for the Creator to intervene on occasions to restore order to the universe. In an 1823 letter to John Adams, Jefferson wrote:
". . . I hold (without appeal to revelation) that when we take a view of the Universe, in it's parts general or particular, it is impossible for the human mind not to percieve and feel a conviction of design, consummate skill, and indefinite power in every atom of it's composition. The movements of the heavenly bodies, so exactly held in their course by the balance of centrifugal and centripetal forces, the structure of our earth itself, with it's distribution of lands, waters and atmosphere, animal and vegetable bodies, examined in all their minutest particles, insects mere atoms of life, yet as perfectly organised as man or mammoth, the mineral substances, their generation and uses, it is impossible, I say, for the human mind not to believe that there is, in all this, design, cause and effect, up to an ultimate cause, a fabricator of all things from matter and motion, their preserver and regulator while permitted to exist in their present forms, and their regenerator into new and other forms. We see, too, evident proofs of the necessity of a superintending power to maintain the Universe in it's course and order. Stars, well known, have disappeared, new ones have come into view, comets, in their incalculable courses, may run foul of suns and planets and require renovation under other laws; certain races of animals are become extinct; and, were there no restoring power, all existences might extinguish successively, one by one, until all should be reduced to a shapeless chaos." [go back] - Another portion of the fossils collected by William Clark in 1807 were deposited in the American Philosophical Society (APS) in Philadelphia. See Discovering the Mastodon: Part 8- Fossils in the White House for more information. After he retired from the presidency in 1810, Jefferson concentrated his efforts on the advancement of education in Virginia. His efforts culminated in the founding of the University of Virginia. He regularly referred natural history inquiries, including those concerning fossils, to the APS. [go back]
- Jeane Baptiste Pierre Antone de Monet, Chevalier de Lamarck (1744-1829) was a rival of Cuvier. Although he was forcefully discredited by Cuvier and others, Lamarck is arguably the first consistent evolutionist. His ideas about the transformation of species were inspired by his work with fossil bivalves, which had exceptionally good fossil records. These fossil series exhibited gradual but discernible changes over time. Given what Lamarck believed to be the immense age of the Earth, he reasoned that the accumulation of gradual changes would —over time— result in the generation of new forms. [go back]
- Darwin believed that evolution was a gradual process because the extinction of less fit forms was occurring all the time. Most evolutionary biologists endorse Darwin's Natural Selection as an essential feature of evolution, but his gradualist model is not quite as widely accepted. One alternative, Punctuated Equilibrium, proposes that individual species typically exhibit little change over their lifetimes, but this equilibrium is punctuated by the rapid evolution of new species. Another modification of Darwin's gradualism is the widespread acceptance of Mass Extinction. These catastrophic events result in the accelerated extinction of a great many species. Although rare, they had profound influences on the History of Life. [go back]