Both naturalists had a love for classification and description but grew up with different influences. Geoffroy came to Paris to study medicine, law and philosophy in early 1789, but shifted to the study of zoology not long after. When a priest mentor of Geoffroy's became caught up in the political turmoil of the revolution of 1789, it was through Geoffroy's testimony that the priest was released from prison. Making friends in the church led to his eventual appointment as a zoology professor in the Royal Garden (later became the Museum of Natural History), when a post was vacated due to more political problems. Although he was only twenty-one years old at the time, this position gave Geoffroy access to resources and natural collections in which he built his future theories on nature. He was even able to accompany Napoleon on an expedition to Egypt in 1798 where he studied mummies and made hypotheses on change over time in humans and other organisms. Geoffroy agreed with Buffon that any classification system was arbitrary and thus somewhat empty, but he nonetheless attempted to find the general laws that applied to all organisms in nature.
Before their well-known rivalry developed, the two scientists began as close colleagues and friends. Cuvier met a member of the Academy of Sciences, Henri-Alexandre Tessier, in Normandy in 1794 while he was a young man tutoring the children of the wealthy. Tessier was impressed by Cuvier's talent and skill, and soon after wrote glowing letters to established scientists like Geoffroy and another, Jussier. Geoffroy was charmed by Cuvier's detailed descriptions of animals and his precise sketches and decided to invite him to "come to Paris. Come play among us the role of another legislator of natural history." When Cuvier joined him at the Museum, other colleagues warned Geoffroy against mentoring him, suggesting that this brilliant young scientist would eventually surpass him. Despite this premonition, both scientists worked side by side and wrote five papers together on the classification of mammals, the two-horned African rhinoceros, species of elephants, descriptions of the tarsier, and the biology of the orangutan. It was not long before Cuvier began to make a name for himself individually too, as he was highly skilled at reaching out to patrons, networking and acquiring funding for his research. By 1976, Cuvier was working on his papers on extinction, merely two years after joining the Museum, while Geoffroy had barely begun to publish. One of the most significant events that solidified the split between the two scientists was Cuvier's appointment to the Academy of Sciences on December 17, 1795 as one of the six original members of anatomy and zoology. Cuvier was only twenty-six years old (seventeen years Geoffroy's junior) and the youngest member at the time, while Geoffroy was not given admittance to the Academy for another twelve years.
Prior to the debate, biological scientists were generally split into two major factions: whether animal structure was determined by functional needs of an animal or the "conditions of existence" (Cuvier), or a basic unified form that was modified across all animal forms (Geoffroy). By determining the answer to this question, scientists could also shed light on the mechanisms of the evolution of species, as well as potentially finding a useful system to classify species to better understand the order of nature. Cuvier was an influential scientist with significant political power and many prominent positions: permanent secretary at the French Academie of Science, a professorship at the Museum of Natural History and the College of France, as well as a Council member at the University of France. Cuvier stuck to "positive facts" of science and refused to flirt with hypotheses and unsupported ideas. This attitude sprang from worries that this kind of thinking would lead to unrest and disorder in France as the French Revolution had torn through only a few decades before. Cuvier encouraged young scientists to stick with facts and often won them over easily due to his strong reputation as a good ally to have in science. His political ties and academic connections gave his ideas a broader audience and generally more historical recognition. Geoffroy was heavily influenced by Buffon and Lamarck. It was in his memoir Philosophie anatomique, published in 1818, that he first put his ideas on animal form and structure into print. Here he attempted to answer his own question, "Can the organization of vertebrated animals be referred to as one uniform type?" Cuvier on the other hand was known as Lamarck's greatest critic, as Cuvier felt Lamarck was too speculative without enough facts to back up his theories. Cuvier grew up reading the works of Linnaeus and was mostly self-taught through dissection and measurements of organisms. Geoffroy thought of facts as building blocks to science while new ideas would lead to real discovery, occasionally dipping more into philosophical hypotheses instead of testable or demonstrated research. Geoffroy kept his unpopular ideas under wraps when advantageous to his career but found it increasingly difficult to stay passive as he got older and more well known. He may even have welcomed the debate between himself and Cuvier as a chance to liven up the discussions in the Academy and generate new ideas.
While the two biologists had disagreed on animal structure subtly through their publications, talks with other scientists at Academy meetings, and in private, a paper on mollusks written by two relatively unknown scientists drew Geoffroy and Cuvier at arms. The paper, written by Meyranx and Laurencet, was assigned to Geoffroy and Pierre André Latreille to review and report to the Academy. Meyranx and Laurencet's conclusions grabbed Geoffroy's attention by suggesting a link between vertebrate and mollusk internal anatomy. With thousands of drawings of mollusks and multiple essays, the authors argued that the organ arrangement of a mollusk resembled vertebrate organ arrangement, if the vertebrate bent backwards so that the neck was connected to the backside. Geoffroy found support for his unity of composition which would unite the vertebrates and mollusks -two of Cuvier's published embranchments of animals- on one common plan.
On February 15, 1830, Geoffroy presented his report to the Academy. In an epilogue that was eventually removed from the final report at Cuvier's insistence, Geoffroy made a clear attack at Cuvier by quoting from a work of Cuvier's from 1817, "Memoir on the Cephalopods and on Their Anatomy", though the author and actual manuscript name were not mentioned. Geoffroy ridiculed the old-fashioned way of describing nature by focusing on differences instead of similarities, presenting his unity of composition theory as a better alternative. Cuvier disagreed vehemently with the report and paper's findings, promising to further explain his argument in future writings.