One Single Plan

For three days – les trois glorieuses – at the end of July 1830, Paris was in turmoil. The attempt by Charles X and his ultra-royalist first minister, the Prince de Polignac, to stamp out liberal discontent with a set of repressive ordinances had backfired. By 28 July, insurgents had raised barricades, taken the Hôtel de Ville, and driven royalist troops out of Paris. Charles fled into exile.

Not surprisingly, these events were followed closely throughout Europe. When the news reached Weimar on 2 August, Frédéric Soret, a visitor from Geneva, recorded that it ‘set everyone in a commotion’. That afternoon, Soret visited Goethe, who was by then in his eighties:

‘Now,’ he exclaimed as I entered, ‘what do you think of this great event? The volcano has come to an eruption; everything is in flames, and we no longer have a transaction behind closed doors!’

‘A frightful story,’ I replied. ‘But what else could be expected under such notorious circumstances and with such a ministry, than that matters would end with the expulsion of the royal family?’

‘We do not appear to understand each other, my good friend,’ replied Goethe. ‘I am not speaking of those people at all, but of something entirely different. I am speaking of the contest, of the highest importance for science, between Cuvier and Geoffroy Saint-Hilaire, which has come to an open rupture in the Académie.’

This expression of Goethe’s was so unexpected that I did not know what to say, and for some minutes felt my thoughts completely at a standstill.

At stake, Goethe believed, was the soul of science. For him, Georges Cuvier was a blinkered pedant – an amasser of facts, bereft of vision – while Etienne Geoffroy Saint-Hilaire embodied the speculative, some might say mystical, approach to science, with its occasional disdain for such irritating details as the facts, which Goethe himself championed. Cuvier, Goethe told Soret, was ‘analytic’ and Geoffroy ‘synthetic’: ‘What is all intercourse with nature, if by the analytic method, we merely occupy ourselves with individual material parts, and do not feel the breath of the spirit, which prescribes to every part its direction, and orders, or sanctions, every deviation, by means of an inherent law?’ Goethe went further: unlike the plodding Cuvier, Geoffroy ‘seeks to penetrate the cause of the universality of things’.

Goethe’s gloss on the debate reflects his own agenda. He saw Geoffroy as the apostle in France of his own ‘synthetic manner of treating nature’. Having decreed him the victor, Goethe set about publicising the victory, writing two articles on the debate, one of which – as supporters of Geoffroy never failed to point out – was his final publication. Goethe’s is one of many conflicting perspectives on the dispute, which, down the years, has become a vehicle for various preoccupations and whims. For example, it’s often represented as an early clash between the reactionary forces of religious conservatism (Cuvier) and the progressive ones of evolution (Geoffroy), yet Geoffroy’s enthusiasm for transformationism – as evolution was known in those days – was, in Stephen Jay Gould’s accurate assessment, ‘fitful’ at best. Even the outcome has been subject to revision. Goethe may have considered Geoffroy the winner, but others have with equal conviction accorded Cuvier the laurels, seeing his as a victory of sound science over waffly Romanticism. What was the dispute about, and why was it so acrimonious? And why has this episode proved so protean in the hands of historians of science?

Geoffroy was born in 1772, the seventh of the 14 children of a provincial barrister. A precocious child, he was steered towards the church, but instead took a bachelor’s degree in law in Paris in 1790. He embarked on a medical career, as a pretext for dabbling in the natural sciences. Many of his teachers were either aristocrats or priests and so it was that at 2 a.m. on 2 September 1792, Geoffroy could be found in disguise up a ladder, helping a group of them make a getaway. Ironically, the Revolution’s anti-intellectual bent ended up working in his favour, when one of the senior scientists at the Jardin des Plantes – then the centre of French natural science – forsook Paris for the provinces, where his aristocratic connections would be less likely to prove lethal. Geoffroy was appointed in his place, and in a matter of months found himself, at the age of 21, elevated to a chair in zoology at the newly founded Muséum d’Histoire Naturelle. He knew nothing about zoology. A tentative interest in mineralogy was all he had to offer as a natural scientist, but qualified people were in short supply in revolutionary Paris, and France, anyway, lacked a scientific tradition in zoology. The other newly appointed zoologist was Jean-Baptiste Lamarck, a botanist, who qualified on the strength of possessing a collection of shells. For Geoffroy, the museum provided an extraordinary opportunity: here, superbly equipped and ambitiously endowed, was the institutional powerhouse that was to be the epicentre of the biological world for the next fifty years.

In 1795, Geoffroy recruited Georges Cuvier, a young and relatively obscure naturalist. Cuvier was born in 1769, in a Protestant region close to the Swiss border, and was educated in Germany. As tutor to the son of a wealthy Protestant family in Normandy, he found time, pottering on the seashore, to refine his long-standing interest in natural history. Word reached Geoffroy, as he groped around in his new discipline, that Cuvier, three years his senior, actually knew some zoology. Despite the prescient concerns of his colleagues at the museum that Cuvier would strive to eclipse his sponsor, Geoffroy collaborated eagerly with his new friend. They collaborated on a number of articles and even lived together for a while. However, Cuvier was both scientifically more sophisticated and politically more astute, and it was not long before he had indeed eclipsed Geoffroy, establishing himself in the process as France’s leading naturalist. Cuvier was elected a member of the Académie des Sciences as early as 1795; Geoffroy had to wait until 1807.

Something of the difference between them can be seen in their responses to an invitation in 1798 to accompany the Napoleonic expedition to Egypt. Ever game for an adventure, Geoffroy accepted enthusiastically; Cuvier, as he recalled in his manuscript autobiography, held back: ‘My calculation was soon made. I was at the centre of science in the midst of the finest collection, and I was sure to do my best work there, more coherent, more systematic, and containing more important discoveries than in the most fruitful voyage.’ Ironically, some of the material Geoffroy brought back from Egypt proved especially valuable to Cuvier in his campaign against transformationism. Mummified animals recovered from burial sites were, Cuvier pointed out, both several thousand years old and indistinguishable from their modern equivalents – proof, surely, that species did not transform over time. Only with the publication of On the Origin of Species did it become apparent that Cuvier’s timescale for evolutionary change was several orders of magnitude too short.

Geoffroy and Cuvier shared an intellectual goal: to explain and organise the diversity seen in nature. From our Darwinian viewpoint, this seems an eccentric thing to do in the absence of a theory of evolution. How is it possible to understand the connections among different forms without an appreciation of the genealogical links among them? In fact, pre-Darwinian biology differed in day-to-day practice very little from the post-Darwinian version. The hunt for patterns of similarity and difference among species was the same, even if the causes – evolution versus divine design – that underlay the patterning were different. Through their studies of comparative anatomy, pre-Darwinian biologists sought to glimpse the workings of the mind of God.

For Cuvier, function was paramount. Species – and their component parts – were designed for particular purposes. The bird’s wing is the perfect flying organ, and the seal’s flipper is perfect for swimming. That there are fundamental structural similarities between the wing and flipper – derived, we can now appreciate, from a common evolutionary ancestor – was irrelevant to Cuvier. Similarities are a result of shared aspects of function, just as the wheel of a wheelbarrow and the paddle-wheel of a riverboat overlap in basic form but diverge according to the specific demands of function. Cuvier was interested in those differences: how the wheelbarrow wheel is suited to transporting materials, and the paddle-wheel to driving boats up rivers. In keeping with his functionalist vision, he emphasised the interplay of the component parts of an animal: the external form of a fish and the physiology of its internal organs come together as an integrated whole to facilitate life in water. Cuvier prided himself on his ability to reconstruct whole organisms from fossil scraps: ‘Every organised being forms a whole, a unique and closed system, whose parts mutually correspond and concur to the same definite action by a reciprocal reaction. None of its parts can change without the others also changing, and consequently each of them taken separately, indicates and determines all the others.’ Whereas Lamarck had divided animals into vertebrates and invertebrates, Cuvier recognised four divisions, or embranchements: vertebrates, articulates (animals such as insects with jointed legs), molluscs and radiates (sea anemones, starfish and other radially symmetrical animals). These categories represented fundamentally different organisations, each one determined by the demands of function.

Whereas structure was subordinate to function for Cuvier, Geoffroy had it the other way round. Structure was everything, function an afterthought. He highlighted the fundamental similarity between the bird’s wing and seal’s flipper, viewing the specific differences between them – the adaptations for their contrasting functions – as incidental. For him, the wheelbarrow wheel and paddle-wheel were all about their shared wheelness. Forget the four embranchements: comparative biology for Geoffroy consisted in the pursuit of the basic structure underpinning all animal design. He laid out his doctrine with uncharacteristic brevity in 1796: ‘It seems that nature is confined within certain limits and has formed all living things on only one single plan.’

Geoffroy was not alone in his vision of the natural world as a set of variations on a single divine theme. Goethe had been so sure that all vertebrates shared the same set of bones – that ‘one single plan’ – that he went to considerable and ingenious lengths to demonstrate that a small bone in the roof of the mouth, thought to be a critical difference between humans and monkeys (humans were supposed to lack it), was in fact present in humans. And in 1790 he published a whimsical pamphlet in which he proclaimed flowers, sepals and other fundamental features of plant morphology to be modified leaves. Even Geoffroy, no stranger to the unscientific presentation of scientific ideas, was struck by Goethe’s style: ‘It is the book of a scientist for its fund of ideas but, in its format, it is the book of a philosopher who expresses himself as a poet.’

Goethe had effectively reduced all plant anatomy to ‘one single plan’, but it was Geoffroy for whom the single plan became an idée fixe. But how could it explain fundamental differences in anatomical organisation between the major groups? For example, in vertebrates the nerve cord runs down the back, whereas in insects and other invertebrates it runs down the front. Simple, Geoffroy said: a vertebrate is an upside-down invertebrate (and vice versa). The distinction between ventral and dorsal was arbitrary, he claimed, because it is based solely on the orientation of an animal to the sun. And, going further in this attempt to explain the match between the vertebrate and invertebrate skeletons, he concluded that insects are single hollow vertebrae, their legs merely vastly modified ribs.

Cuvier was squirming. His colleague seemed hell-bent on breaching the divisions between his beloved embranchements and, worse, he was ignoring legions of biological facts as he tried to make the natural world fit his unitary model. But Cuvier, as was appropriate for someone in his exalted position, was restrained in his attacks. In 1828, he began a major work by insisting that ‘Natural History is a science of facts,’ and noted that those who saw evidence of unity of composition in the natural world were ‘more poets than observers’. Finally, however, he was pushed too far. Two unknown naturalists (so unknown that generations of historians have been unable to determine the first name of one of them) conjectured a link between molluscs and vertebrates. If, they argued, a vertebrate is bent backwards and the nape of its neck attached to its buttocks, you get something not too far removed in overall organisation from a cuttlefish. Geoffroy was delighted – another pair of embranchements had been linked – and Cuvier went ballistic.

The resulting debate that played out at the Académie des Sciences over the first half of 1830 was inevitably nasty. Cuvier had bottled his opinions up for too long, and matters were complicated by the spectre of a once warm relationship turned sour, and by Cuvier’s nagging knowledge that Geoffroy, by bringing him to Paris all those years ago, had been responsible for his first big scientific break.

The dispute was as much about the data – did the facts of comparative anatomy support Geoffroy’s conjectured transformations? – as about two different approaches to science: structuralism versus functionalism. Cuvier, always the better facts man, definitely won the first part of the debate, but the controversy over philosophical issues was destined to be inconclusive. And that, presumably, is one reason why Goethe and every subsequent commentator have been able to find support for their preferred interpretation in the record of proceedings. Even in our post-Darwinian world the debate remains alive and well. To what extent are the attributes of organisms optimal solutions – courtesy natural selection – to the functional problems of surviving and reproducing in a particular environment, and to what extent heirlooms from the evolutionary past? The wonkiness of the human knee bears witness to the interplay of these factors: natural selection did not start from scratch to bio-engineer the perfect joint for an upright bipedal animal, but had instead to modify the materials to hand – namely, a quadruped knee joint. Our knee is a compromise between the historical constraints of structure and selection for improved function. It’s hardly surprising that the result is so injury prone.

The importance of the debate lies in the way it shaped the mindset of 19th-century biologists. Darwin’s theory was a resounding endorsement of both viewpoints: his mantra that all of the natural world is genealogically connected thanks to ‘descent with modification’ is pure structuralism, while his emphasis on natural selection as the mechanism promoting adaptive change is pure functionalism. In her excellent 1987 account of the debate, Toby Appel argues that both protagonists ‘defended extreme positions’. As so often in scientific disputes, the truth lay somewhere in the middle; and so, Appel points out, the debate’s significance lay in its challenge to ‘naturalists to come to a creative resolution’ of the schism. That was Darwin’s achievement.

It’s easy to dismiss Geoffroy as a crank. He didn’t help matters in his later years by publishing an endless catalogue of stream-of-consciousness articles with cumbersome titles such as ‘There Is Only a Single Physics in the Universe in Which the Worlds Weigh against Each Other, Communicating by an Immense Molecular Diffusion, Sublime Attenuation of Matter (Imponderous Elastic Gases), and Are Regulated by Means of the Principle (Attraction of Soi pour Soi)’. However, his reputation is rather unexpectedly being refurbished by recent findings in molecular biology. Now that the Human Genome Project has been completed, DNA-sequencers have turned their attention to other species, with the result that the modern equivalent of the Geoffroy/Cuvier science of comparative anatomy is comparative genomics. The findings are striking. Not only do humans have surprisingly few genes (approximately thirty thousand), but the ones we have are shared by other species. Every human gene has a recognisable counterpart in the mouse genome, despite the two species’ being separated evolutionarily by some 75 million years. Even the lowly puffer fish has basically the same complement of genes as we do. And we don’t have to confine ourselves to vertebrates: despite a separation of half a billion years, 61 per cent of fruit fly genes (from a total of 14,000) have human equivalents, and a millimetre-long nematode worm (19,000) shows a 49 per cent match-up. Animals, it seems, share a basic genetic toolkit, and the challenge for modern biology is to work out the paradox of how, in the face of the constraints imposed by these fundamental similarities, so many differences have evolved. Geoffroy must be spinning cheerfully in his grave as molecular biologists reveal in ever more detail the extent to which there is ‘only one single plan’.

And the news gets even better for Geoffroy. Again in the light of molecular biology, some of his wackier ideas have proved less wacky than Cuvier and generations of biologists have supposed. The genes involved in determining the dorsal/ventral axis of the developing embryo (i.e. which side of an embryo is up, and which down) in both insects and vertebrates are equivalents, both ultimately derived from a single set of genes in the ancient common ancestor of both insects and vertebrates. The curious thing is that they have been switched: the genes that specify ‘ventral’ in insects are the ones that specify ‘dorsal’ in vertebrates (and vice versa). Their equivalence has been demonstrated experimentally: add a dorsal-specifying human gene to a mutant fruit fly lacking its normal ventral-determining gene, and you get a normal fruit fly. The human dorsal gene has substituted for the missing fruit fly ventral gene. It seems that Geoffroy’s vision of vertebrates as upside down insects is – at this level of analysis, anyway – amazingly close to the mark. Goethe, too, is enjoying a bout of posthumous vindication. Molecular biological analysis of the development of flowers has shown that his idea that plant organs are all variations on a single leafy theme is sound. There are mutations that cause a plant to produce flowers that are nothing more than green leafy rosettes.

The Geoffroy renaissance isn’t confined to dark corners of molecular biology labs. Interest in the way developmental pathways have been tweaked to generate biological novelty is so strong that the field now has its own (ghastly) name: ‘evo-devo’. The appearance in English of Hervé Le Guyader’s study is timely. But the book, whose primary purpose is to republish several of Geoffroy’s most important works, is only for real aficionados. Those reluctant to grapple with Geoffroy’s prose – frequently impenetrable even in translation – would do better with Appel’s account, which provides plenty of background to the Cuvier/Geoffroy showdown.

Although molecular biology has proved some of Geoffroy’s hunches correct, others – such as his insistence that insects inhabit their own vertebrae and walk on their ribs – will probably remain among science’s misbegotten theories. His real contribution, as a precursor of Darwin, lay in his vision of an interconnected natural world in which similarities in structure revealed either the nuances of the divine mind or – after Darwin – genealogical affinities. It is, however, only when his ideas are juxtaposed and stitched together with those of his lifelong rival and sometime friend that it’s possible to appreciate the remarkable extent to which early 19th-century biology presaged Darwin’s theory of evolution.