"The external world is all-powerful in alteration of the form of organized bodies.. . these [modifications] are inherited, and they influence all the rest of the organization of the animal, because if these modifications lead to injurious effects, the animals which exhibit them perish and are replaced by others of a somewhat different form, a form changed so as to be adapted to the new environment."Geoffroy Saint-Hilaire, "Influence du monde ambiant pour modifier les formes animales." 1833.
Étienne Geoffroy St. Hilaire was born on April 15, 1772, in
Étampes, near Paris, France.
Receiving a law degree in 1790, he went on to study
medicine and science in Paris, at the Collège du Cardinal Lemoine.
When the Reign of Terror struck, Geoffroy risked his life to save some of
his teachers and colleagues from the guillotine. Managing to keep his own
head, Geoffroy was appointed a professor of vertebrate zoology at the Jardin
des Plantes, which under the Revolutionary government
soon was reformed and renamed the Musée National d'Histoire
Naturelle. In 1794, on the recommendation of Henri Alexandre Tessier, a
naturalist who had fled to Normandy to escape the Reign of Terror,
Geoffroy extended a fateful invitation to the young naturalist
Georges Cuvier to
come to Paris. Cuvier and Geoffroy collaborated on several research projects.
Geoffroy accompanied Napoleon's invasion of Egypt in 1798, and brought back
many animal specimens to Paris, notably mummified cats and birds, which Cuvier
would later study and cite as proof that evolution had not occurred. In 1807
Geoffroy was named to the Academie des sciences;
in 1809 he became a professor of
zoology at the University of Paris. After his death on June 19, 1844, his
son Isidore succeeded to this position; Isidore was a prominent zoologist
and embryologist in his own right.
The zoologist and historian of science E.R. Russell summed up the great
biological controversy of the first half of the nineteenth century: "Is
function the mechanical result of form, or is form merely the manifestation
of function or activity? What is the essence of life -- organization or
activity?"
While Cuvier
founded the "functionalist" school of organismal biology, with his insistence
on animals as functionally integrated wholes, Geoffroy continued the more
"formalist" tradition of biology that had started with
Buffon and was
being continued by Goethe,
Lamarck,
and others. In his 1818 book Philosophie anatomique, Geoffroy
asked the question: "Can the organization of vertebrated animals be referred
to one uniform type?" The answer for Geoffroy was yes: he saw all vertebrates
as modifications of a single archetype, a single form. Vestigial organs
and embryonic transformations might serve no functional purpose, but they
indicated the common derivation of an animal from its archetype.
Cuvier insisted that similarities between organisms could only result from
similar functions, writing in 1828, "If there are resemblances between the
organs of fishes and those of the other vertebrate classes, it is only insofar
as there are resemblances between their functions." This viewpoint is
diametrically opposed to Geoffroy's view; he
wrote in 1829: "Animals have no habits but
those that result from the structure of their organs; if the latter varies,
there vary in the same manner all their springs of action, all their
faculties and all their actions."
Geoffroy spent much time drawing up rules for deciding when structures in
two different organisms were variants of the same type -- in modern
terminology, when they were homologous. His criterion was connections
between parts: structures in different organisms were the same if their parts
were connected to each other in the same pattern.
As Charles Darwin described his work in 1859, in The Origin of Species:
Matters came to a head in 1830, when two young naturalists,
Meyranx and Laurencet, presented a comparison of the anatomy of vertebrates
and cephalopods (squids, cuttlefish, and octopi), claiming that they were
based on the same basic structural plan. Geoffroy enthusiastically adopted
this claim as proof of the unity of plan shared by all animals; Cuvier
could not reconcile it with the results of his careful anatomical research.
Thus was set up one of the most famous debates in the history of biology:
eight public debates between Cuvier and Geoffroy, from February to April 1830.
In these debates, Cuvier showed convincingly that many of Geoffroy's supposed
examples of unity of structure were not accurate; the similarities between
vertebrates and cephalopods were contrived and superficial. However, Geoffroy's
ideas continued to circulate, and inspired later scientists, in particular
Richard Owen and
Karl Ernst Von Baer, to synthesize the positions of Cuvier and Geoffroy.
Despite their differences, the two men did not become enemies; they respected
each other's research, and in 1832 Geoffroy gave one of the orations at
Cuvier's funeral.
It would be an error to call Geoffroy an evolutionary biologist in anything
like the modern sense. Geoffroy's field was morphology -- the study of form,
pure and simple, not of the evolutionary history of forms. The archetypal
forms of Geoffroy's "transcendental zoology" were abstractions, not once-living
ancestors; shared archetypal form did not necessarily indicate common ancestry.
In this respect, Geoffroy's zoology resembled Naturphilosophie, a German
metaphysical philosophy that sought for correspondences and connections between
humanity and nature. In many of his writings, Geoffroy left open the actual
origins of organisms.
However, later in his career, Geoffroy published some
ideas that resemble the theory of evolution by natural selection. The quote at
the top of the page shows that he considered that heritable changes in an
organism might be selected for or against by the environment, and thus that
present-day species might have arisen from antediluvian (before the Biblical
Flood) species. He had studied embryology and in
particular teratology (the study of abnormal development) and suggested that
morphological change was not slow and gradual, as Lamarck had proposed,
but rather occurred in bursts that were caused by changes in embryological
development. Like his concepts of "Unity of Type," these ideas would
rise to prominence in later evolutionary
theories. Darwin himself cited both the elder Geoffroy Saint-Hilaire and his
son Isidore (who had continued to develop some of his father's ideas) as
persons who had anticipated his theory to a certain degree (Darwin, 1861). But
these ideas apparently were never a key part of Geoffroy's thought. Geoffroy
believed that there were limits to how far an organism might evolve, and he
never developed his ideas into a complete theory, as Darwin later did.
Does form or function determine the phenomena of life? Echoes of Cuvier's
debate with Geoffroy persist to the present day; many organismal biologists
lean towards "formalist" or "functionalist" schools of thought. Yet
part of the power of modern evolutionary biology comes from its ability to
synthesize elements from both schools of thought. Organismal lineages change
with time, in response to changing environments, and their form constrains
the functions that they can take on; at the same time, it is the ability of
organisms to function in their environments that is a major component of
evolutionary fitness, and form is often altered to fit a particular function.
Cuvier and Geoffroy had grasped separate parts of a more complex reality.
What can be more curious than that the hand of a man, formed for grasping, that
of a mole for digging, the leg of the horse, the paddle of the porpoise, and
the wing of the bat, should all be constructed on the same pattern, and should
include the same bones, in the same relative positions?
Geoffroy St. Hilaire has insisted strongly on the high importance of relative
connexion in homologous organs: the parts may change to almost any extent in
form and size, and yet they always remain connected together in the same order.
Geoffroy was among the first to grasp an extremely important concept.
For Charles Darwin and for evolutionary biologists after him, defining and
identifying homologous structures became both an important source of support
for evolution and an important tool for identifying
evolutionary relationships. However, in hindsight, Geoffroy
stretched many examples of homology, or "Unity of Type," farther than
was warranted by the evidence available. One of his more infamous theories was
that the segmented external skeleton and jointed legs of
arthropods
such as insects were equivalent to the internal vertebrae and ribs of
vertebrates;
insects literally live inside their own vertebrae and walk on
their ribs. He is said to have stated, "There is, philosophically speaking,
only a single animal." Theories like this, which though ingenious
often required great stretching of the
evidence, drew the ire of Cuvier, who had become the greatest zoologist of
the time, and who had a reputation as a meticulous scientist.