May 8^th 1794 was a bad day for 36 years old Marie-Anne Paulze. First her father, then her husband, walked up the scaffold in Place de la Concorde to be guillotined.

They had upset the revolutionaries by defending the old attitudes and ways of conducting their tax-collecting business. More important had been the unfortunate status of Marie-Anne’s husband, Antoine Lavoisier.

He was Europe’s leading chemist and a prominent aristocrat. No-one seemed too sure what he had done wrong but in the end that didn’t really matter; he was just on the wrong side, in the wrong place at the wrong time.

In England, that same month, the first volume of Zoonomia or the laws of organic life, which Erasmus Darwin had been working on for several years, was eventually published. The 586 quarto pages weighed 2 kilos and contained 200,000 words. 

It had very useful data about the kinds of illnesses that medical practitioners could expect to examine through their daily rounds, an invaluable daily guidebook. But the devil was in the detail, hidden at the end as Chapter 39, and unnoticed for almost a year, was Erasmus Darwin’s flawed but poignant case for transmutation.

This was the first and final time that he wrote about his theory in any detail though he often spoke about it in private. That was because it was just a hunch, a clever idea without any evidence and he knew it lacked credibility until some evidence was found. The theory was that all life was descended from a single source, a simple group of cells. Furthermore, he thought there may be a link between this early group of cells and the cluster of cells found in living embryos. It was a lot for most people to absorb and understand as the first full account of evolution.

But there was serious trouble for some in Erasmus Darwin’s circle of enlightened thinkers. There was suspicion that their activities might lead to a French style Reign of Terror in England and the government took the rumours seriously enough to institute imprisonment without trial. In 1794, ten of these likely revolutionaries were arrested and thrown into the Tower of London.

Meanwhile, members of the Lunar Society felt highly vulnerable, for as reformers they were associated with Napoleon and thus seen as potential traitors. Already, Priestley had migrated to Pennsylvania, James Watts’ son had gone into hiding after associating with some of the Paris revolutionaries and Erasmus Darwin’s writing made him a target of suspicion as well. These were not good times for challenging the church or the state: it would have been ironic for Erasmus Darwin to have been transported to Botany Bay but there was a distinct possibility of this at the time, especially during the trial of the ten prisoners in the Tower.

When the trial was over the press and then the public turned their attention to Chapter 39 of Zoonomia, Darwin’s ideas of how animals had evolved. They were still very sketchy but they were wisely chosen reasons to explain how animals changed to become new species, ideas firmly based on his lifetime’s experience as a doctor and as an astute observer of nature. He may have discussed transmutation at the Lunar Society meetings but there are no detailed accounts of how his thoughts developed. There’s no telling either whether he ever read Diderot’s 1749 novel Letter on the Blind for the Use of Those Who See, the only other concise writing about evolution and adaptation to the environment that came before Zoonomia’s Chapter 39.

In Darwin’s 55 pages were several examples of variation within single species, how animal and plant varieties changed by controlled breeding, and how some freshly acquired features were transmitted from one generation to another as newly stable characters. One of his most sophisticated suggestions was posed as a very good question that his grandson was soon going to answer:  “Would it be too bold to imagine – that all warm-blooded animals have arisen from one living filament? – with the power of acquiring new parts, attended with new propensities, and thus possessing the faculty of continuing to improve by its own inherent activity, and of delivering down those improvements by generation to its posterity, world without end?” In promoting his ideas about how living species change Chapter 39 clearly described Erasmus Darwin’s ideas about sexual selection and gave examples of adaptation to changing environments.

These developments near the end of the eighteenth century came together as another clear event in the history of how we understood the evolution of life systems. By then, geologists had models of the earth and how it changed, naturalists had indexed the flora and fauna of temperate climates and were exploring beyond. There were still countless philosophical and political problems with biblical interpretation and how that sat beside scientific results. The Flood, the age of the earth and living things, the length of geological time scales, whether or not species became extinct and how they originated: all these questions still went unanswered. The arguments and fierce debates continued, scientific discoveries increased and political and social changes exacerbated the ferment: revolutionary times, indeed.

Paris was a slightly less dangerous place inJanuary 1796, though memories of the reign of terror from two years before were still felt on the streets and revolution was still in the air. But the cafes were places where plenty of new and stimulating thoughts were being tossed about, made all the more exciting by the danger of what might happen with the new authorities. At least the work of the Enlightenment thinkers now had a good chance to break through some of the assumptions that came with a strict interpretation of Genesis. The new observations were being treated scientifically, the collections from expeditions curated, results from experiments logged. But this was still driven, directly and indirectly, by fear.

One of the new ideas was based on a remarkable piece of scientific evidence about life’s history, evidence to show that species could become extinct. George Cuvier (1769-1832) lectured that month at the National Institute of Sciences and Arts On the Species of Living and Fossil Elephants. It was a triumphant inaugural lecture for the 27 year old zoologist about the latest discoveries of more mammoth bones from rock outcrops near Paris and he gave such a dramatic conclusion that immediately he became a well-known figure in post-revolutionary France. Some people thought he went too far, in danger eventually of becoming one of the kind whom the terror had targetted.

In his lecture Cuvier challenged the work of Buffon, the earlier Director of the Museum who had died eight years before under the old regime. Cuvier had examined several new specimens and was able to make better reconstructions, explaining his outrageous suggestion that the Paris mammoth was a distinct fossils species and not, as Buffon always insisted, one whose fossil bones were those of an undiscovered living species.

If the mammoth were a living species it would have been discovered by now from somewhere with a Siberian climate. Since this had not happened, it meant that extinction was part of the evolutionary process and that the old environments of the former world had also disappeared. It meant that back in deep time, before the existence of humans, the world had been a very different sort of place.

It was a fitting time to be talking about catastrophe and extinction. As if to offer themselves to the sacrifice, the old Jardin du Roi and the Cabinet du Roi, institutions implicitly covering the study of living and dead organisms, had just been reconstituted as the Museum Nationale d’Histoire Naturelle. The staff were looking forward to more productive studies of natural history after years of just putting labels on the specimens and trying different ways of sorting them.

The experts at the museum led the way for most other Parisians to be cautiously optimistic that new technology and exploration would improve their lives. The scientists at the museum didn’t have to wait long, for soon they were to get more excitement than any museum had ever experienced. Cuvier’s lecture marked the start of several decades during which their little group was leading the world into important new ways of understanding biodiversity and its transmutation, how the meaning of life changed through many different scales of time.

Cuvier was born near Stuttgart in a small Lutherian francophone enclave. At the start of the revolution, when he was twenty years old, he had lived in Normandy working as tutor to a Protestant family, work which gave him sufficient time for his passionate interest in natural history, especially the anatomy of mammals. He saw some of the mob violence in Caen and had the good sense to keep a low profile. Eager for higher things, he took advantage of the optimistic times and in 1795 he found himself a post at the new National Museum. There, he was just the kind of bright young man from a lower class that the revolution attracted to academic work. So he was easily recruited and worked well alongside another young man who was in charge of the mammals, Geoffroy Saint-Hilaire (1772-1844). They quickly became close friends, and shared living accommodation in the grounds of the museum.

The elephant lecture had made Cuvier well-known, partly through his beautiful and detailed reconstructions of large mammal skeletons from the newly discovered fossils. They were on display in the museum with fossil bones that had also been discovered from the Netherlands, Ohio and Siberia. By the end of 1797, with some help from Geoffroy he had assembled five species, and to what looked very much like a modern elephant they added a mammoth, a giant sloth that Cuvier named Megatherium,

a bear and a rhino, all carefully described anatomically and all showing different features from any of the modern relatives that were then known. Cuvier suspected they were all extinct and had lived just before something like a major environmental event, or “revolution” as he called it: one of Buffon’s catastrophes. But he couldn’t be completely sure that the animals weren’t still roaming around in some unexplored corner of the world, so he was very careful about what he said in public. More positively, he looked to the geologists for evidence of any events which could explain how the extinctions may have led to the modern species. The geotheory models that De Luc and Pallas had proposed a few years before, in 1778, gave him support to fit his work to their theory that one or more revolutionary events caused the extinctions.

Cuvier offered the most topical explanation as the driver of evolutionary change: revolution. It was with that level of real excitement that he described the environmental events that his geological observations suggested would change a species’ life-style and maybe even make it extinct. Working very carefully, putting together the fossil bones of large mammals being collected from the younger clays of the Paris basin and from the chalk around Maastricht, the function of each part was always at the centre of Cuvier’s mind. This was because he was primarily an anatomist with great insight into the beauty and use of the structures he observed. There was a big difference between the mammals from the clays and the few small ones just below the chalk. Their limbs suggested very different gait and the jaws tackled food with other movements and pressures. It made him think there had been a great natural catastrophe between the two strata and he tentatively suggested that an age of reptiles had preceeded the age of mammals.