Étienne Geoffroy St. Hilaire (1772-1844)

"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:

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.

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.