"Why has not anyone seen that fossils alone gave birth to a theory about the formation of the earth, that without them, no one would have ever dreamed that there were successive epochs in the formation of the globe."Georges Cuvier, Discourse on the Revolutions of the Surface of the Globe
Without a doubt, Georges Cuvier possessed one of the finest minds in history.
Almost single-handedly, he founded vertebrate paleontology as a scientific
discipline and created the comparative method of organismal biology, an
incredibly powerful tool. It was Cuvier who firmly established the fact of
the extinction of past lifeforms. He contributed an immense amount of
research in vertebrate and invertebrate zoology and paleontology, and also
wrote and lectured on the history of science.
Biography of Cuvier
Cuvier was born on August 23, 1769, at Montbéliard, a French-speaking
community in the Jura Mountains that was not under French jurisdiction at the
time; it was ruled by the Duke of Württemberg. Cuvier studied at a school
which the Duke had founded, the Carolinian Academy in Stuttgart,
from 1784 to 1788. He then took a position as tutor to a noble family
in Normandy, which kept him out of the way of the worst of the
violence of the French Revolution; there he was named to a position in the
local government and began to make his reputation as a naturalist. In 1795,
Geoffroy
Saint-Hilaire invited him to come to Paris; he was appointed an assistant,
and shortly thereafter a professor of animal anatomy, at the newly reformed
Musée National d'Histoire Naturelle (National Museum of Natural
History). Cuvier stayed at his post when Napoleon came to power, and
was appointed to several government positions, including Inspector-General of
public education and State Councillor, by Napoleon. Cuvier continued as a
state councillor under three successive Kings of France; he thus accomplished
the almost unbelievable feat of serving under three different, opposing
French governments (Revolution, Napoleonic, and monarchy) and dying in his
bed. All the while, Cuvier lectured and did research at the Musée
National, amazing his colleagues with his energy and devotion to science.
By the time of his death he had been knighted and made a Baron and a Peer of
France.
Cuvier's Scientific Thought
Cuvier saw organisms as integrated wholes, in which each part's form and
function were integrated into the entire body. No part could be modified
without impairing this functional integration:
Cuvier's insistence on the functional integration of organisms led him to
classify animals into four "branches," or embranchements:
Vertebrata,
Articulata (arthropods and
segmented worms), Mollusca (which at the
time meant all other soft, bilaterally symmetrical invertebrates), and Radiata
(cnidarians and
echinoderms). For Cuvier,
these embranchements were fundamentally different from
each other and could not be connected by any evolutionary transformation.
Any similarities between organisms were due to common functions, not to
common ancestry: function determines form, form does not determine function.
Cuvier's ideas led him to oppose the theories of his contemporaries, such as
Buffon,
Lamarck, and
Geoffroy St.
Hilaire, who suggested that animal morphology might
be much more changeable and be affected by environmental conditions. They
pointed to vestigial, functionless structures and to embryonic development
to show that dissimilar organisms with different functions might nonetheless
share a common structural plan. Cuvier and Geoffroy engaged in a famous
public debate over their different philosophies in 1830, at the
Académie Royale des Sciences in Paris. While Cuvier is generally
said to have won the debate, the views of Geoffroy continued to be perpetuated
in scientific circles, and the repercussions of this debate on form versus
function can still be felt in modern biology.
Perhaps Cuvier's most crucial and longest-lasting contribution to biology
was establishing extinction as a fact. For over a century before Cuvier,
fossils had been accepted as the remains of once-living organisms, as
scientists like Leonardo da Vinci and
Robert Hooke had
stated. Some scientists believed that many fossils represented life forms that
no longer existed: Buffon, for instance, wrote
prophetically that "We have monuments taken from the bosom of the Earth,
especially from the bottom of coal and slate mines, that demonstrate to us
that some of the fish and plants that these materials contain do not belong
to species currently existing." But others who had studied fossils
could not believe that God, having created all things and pronounced them
good, would allow any of them to be wiped out. Some scientists interpreted
fossils as remains of living species: fossil mammoths found in Italy
were interpreted as the remains of the elephants brought by Hannibal when
he invaded Rome. Others thought that the unusual organisms then known only
as fossils must still survive in unexplored parts of the world -- no less
a personage than Thomas Jefferson, the third president of the United States,
speculated that mammoths might yet be found
living in the American wilderness. While speculation raged, the detailed
information needed to solve the problem had never been collected. As Cuvier
stated in 1796 before the National Institute of Sciences and Arts in Paris,
concerning fossil elephants:
What had happened to these great beasts of the past? Cuvier believed that the
Earth was immensely old, and that for most of its history conditions had been
more or less like those of the present. However, periodic "revolutions", or
catastrophes (a word which Cuvier avoided because of its quasi-supernatural
overtones) had befallen the Earth; each one wiped out a number of species.
Cuvier regarded these "revolutions" as events with natural causes, and
considered their causes and natures to be an important geological problem.
Although he was a lifelong Protestant, Cuvier did not explicitly identify
any of these "revolutions" with Biblical or historical events. However,
some later geologists, notably Rev. William Buckland in England, suggested that
the most recent revolution was the Biblical Flood. This remained
a popular hypothesis until
Louis Agassiz
(who had studied with Cuvier) showed that the "flood deposits" were
actually formed by glaciers.
Cuvier's theory of "revolutions" was later supplanted by uniformitarian
theories, notably those of Lyell. However, with the increased interest in mass
extinctions and their causes, catastrophes have re-emerged as valid hypotheses
for at least some of the great episodes of change in the Earth's biota, such
as the Cretaceous-Tertiary extinction event.
Certainly Cuvier's realization that extinction is real was a great advance for
science. Furthermore, Cuvier's integration of organismal function into the study
of form would prove to be a powerful tool for biologists. In a sense, modern
evolutionary thought has synthesized both Cuvier's views and those of
his opponents into a coherent whole.
. .. the component parts of each must be so arranged as to render possible the
whole living being, not only with regard to itself, but to its surrounding
relations, and the analysis of these conditions frequently leads to general
laws, as demonstrable as those which are derived from calculation or
experiment.
Cuvier did not believe in
organic evolution, for any change in an organism's anatomy would have rendered
it unable to survive. He studied the mummified cats and ibises that Geoffroy
had brought back from Napoleon's invasion of Egypt, and showed that they were
no different from their living counterparts; Cuvier used this to support his
claim that lifeforms did not evolve over time. Organisms were functional
wholes; any change in one part would destroy the delicate balance.
But the functional integration of organisms meant that each part
of an organism, no matter how small, bore signs of the whole. Thus it
was possible to reconstruct organisms from fragmentary remains, based on
rational principles. Cuvier had a legendary ability to reconstruct organisms
from fragmentary fossils, and many of his reconstructions turned out to be
strikingly accurate. However, in practice, he based his reconstructions less
on rational principles than on his deep knowledge of comparative anatomy of
living organisms.
It is evident that one cannot say anything demonstrable about the problem
before having resolved these preliminary questions, and yet we hardly possess
the necessary information to solve some of them. The studies of elephant
bones published up until now contain so little detail that even today a
scientist cannot say whether they belong to one or another of our living
species, and of the enormous quantity of fossil bones about which so many
writers have spoken, we have good drawings of only two or three.
Cuvier went on to publish detailed studies of elephant anatomy that showed
not only that the African and Indian elephants were distinct species, but that
the fossil mammoths of Europe and Siberia were different from either living
elephant species. The picture at left, from his paper of 1798, clearly shows
the differences between the lower jaw of a fossil mammoth (top) and of a living
Indian elephant (bottom) (click on the image to view an enlarged version).
Cuvier went on to publish the results of study after study
documenting the past existence of large mammals that resembled no living
species: the giant ground sloth, the
Irish
elk, the American mastodon, and many others. With these studies, Cuvier
launched modern vertebrate paleontology.
The Muséum National d'Histoire Naturelle,
where Cuvier worked and lectured, is accessible on the WWW.
