At the opening of the National Institute of France in April in 1796, he read his first palaeontological paper. At the time, it was still widely believed that no species of animal had ever become extinct, because God’s creation had been perfect. In his paper, Cuvier analyzed skeletal remains of Indian and African elephants as well as mammoth fossils, demonstrating that African and Indian elephants were different species and that mammoths were not the same species as either African or Indian elephants and therefore must be extinct.
In the second paper he presented in 1796, Cuvier demonstrated that a large skeleton found in Paraguay, which he named “megatherium,” represented yet another extinct animal and, by comparing its skull with living species of tree dwelling sloths, that it was a kind of ground dwelling giant sloth. Together these two 1796 papers essentially ended what had been a long running debate about the reality of extinction.Cuvier believed that organisms were functional wholes; their functional integration meant that each part of an organism, no matter how small, bore signs of the whole. In a 1798 paper on the fossil remains of an animal found in some plaster quarries near Paris, he wrote:
Today comparative anatomy has reached such a point of perfection that, after inspecting a single bone, one can often determine the class, and sometimes even the genus of the animal to which it belonged, above all if that bone belonged to the head or the limbs. … This is because the number, direction, and shape of the bones that compose each part of an animal’s body are always in a necessary relation to all the other parts, in such a way that – up to a point – one can infer the whole from any one of them and vice versa.
This idea is sometimes referred to as “Cuvier’s principle of correlation of parts.” Thus, Cuvier was able to use his deep knowledge of the comparative anatomy of living organisms to produce reconstructions of organisms from fragmentary fossils, many of which turned out to be strikingly accurate.
Ironically, Cuvier’s insistence on the functional integration of organisms prevented him from accepting biological evolution, for he believed that any change in an organism’s anatomy would have rendered it unable to survive. Since organisms were functional wholes, any change in one part would destroy their delicate balance. He also pointed out that Napoleon’s expedition to Egypt had retrieved animals mummified thousands of years previously that seemed no different from their modern counterparts.
To explain the discontinuities seen in the fossil record, Cuvier hypothesized that a vast number of species was originally created in the beginning and that, although the Earth was immensely old and for most of its history conditions had been more or less like those of the present, periodic “revolutions” had occurred, each causing the extinction of many species of animals. This view came to be known as “catastrophism.” 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. The species we see today, according to his hypothesis, are the species that were present at the beginning and whose unmodified descendants have survived all the later catastrophes. (Unfortunately for Cuvier, the lowest and oldest layers of sedimentary rock do not contain any fossils of present-day species that would be expected if his hypothesis was correct.)
The harshness of his criticism and the strength of his reputation continued to discourage naturalists from speculating about the transmutation of species, right up until Charles Darwin published The Origin of Species more than two decades after Cuvier’s death.