On a Bet, Jean-Baptiste Lamarck Invented the Way We Still Identify Plants

If you’re an herbivore, constantly in danger of being devoured by a lion, you must do a lot of running, and you become slender and swift. If an idiot friend has attempted to lift you by the head, causing a career-changing neck injury (unless it was scrofula), and then your overbearing older brother has refused to let you become a musician, and then you’ve unsurprisingly turned out to detest banking, and then that same overbearing older brother has borne you off to a bucolic retreat for a year, where you’ve fortuitously gotten to go botanizing with Jean-Jacques Rousseau himself, but your family still wants you to adopt a practical profession, such as medicine, you decide to try a bet-hedging sort of combined approach: medicine, okay, but also botany.

At age twenty-eight, Jean-Baptiste Lamarck began training in both subjects concurrently. For several years he followed courses in anatomy, physiology, and botany at the King’s Garden and the School of Medicine in Paris, including those taught by the young comparative anatomist Félix Vicq d’Azyr, four years Lamarck’s junior. Vicq d’Azyr performed dramatic and rather creepy demonstrations that, even decades later, remained in Lamarck’s mind, such as when he showed that a severed frog’s heart would respond to stimulus as much as twenty-four hours after its removal from the frog, thereby demonstrating the great irritability of tissues in simple animals.

But at the time, it was a radical and downright Rousseauian bet. It meant that botany was not the preserve of scholars writing in Latin. On the contrary, botany was a walk in the park, a pastime for the people.

To these formal curricula, Lamarck added a third subject in the form of an independent study. From the high, narrow window of his Parisian garret, he could see nothing but clouds; contemplating these, he became a student of meteorology. The formation and dispersal of clouds was the subject of Lamarck’s first remarks before the Royal Academy of Sciences. Around the same time, he also began a collection of shells that grew to become one of the biggest and most beautiful in the city; this was a fashionable pursuit and an expensive one, but he probably struck a deal with some Parisian shell merchants, trading his growing expertise for occasional rare specimens.

In this way, by self-exertion and adaptive response to environmental pressures and possibilities, Lamarck by around age thirty had undergone a veritable transformation of species from a brash, adventure-seeking teenager to a contemplative naturalist immersed in the many forms of living things and their constantly changing milieu.

In his early thirties, while engrossed in these studies, Lamarck also became romantically involved with a woman named Rosalie de la Porte. The two moved in together to an apartment right at the geometric center of Paris in the rue des Deux Ponts, which vertically bisects the Île Saint Louis, where it sits in the middle of the Seine separating the Left and Right Banks. They would remain together until her death fifteen years later, and they would have six children together.

Rosalie de la Porte was apparently good for Lamarck’s productivity. Soon after they got together, in 1778, Lamarck produced his two first works—French Flora in three volumes and a baby girl named for her mother, Rosalie Joséphine, who would remain her father’s closest companion for the rest of his life. Much later, when Lamarck was old and blind, this Rosalie would be his amanuensis, reading to him, conducting research for him, and even writing for him. Soon after baby Rosalie’s birth, the family moved southward onto the Left Bank following the direction of Lamarck’s botanical ambitions, leaving the rue des Deux Ponts for the rue Copeau (now the rue Lacépède), a street that runs down the Montagne Sainte-Geneviève directly into the northwest corner of the King’s Garden.

And it was there in the garden, around that same time, according to Auguste, that a casual bet with some friends led Lamarck to write French Flora. One day, strolling with some fellow botany students, he remarked that he could enable the first passerby, whoever it might be, to identify any plant in the garden. All he’d need would be to first explain to the person the basic distinguishing features of plants. When the friends took him up on the bet, he requested a little preparation time. Soon afterward, they gathered back in the garden, accosted the first passerby, and hey, presto! Before their very eyes, Lamarck transformed the person into an amateur botanist, clinching the metamorphosis with a successful plant identification. Today, the idea of turning any random passerby into an amateur botanist may not seem extraordinary. But at the time, it was a radical and downright Rousseauian bet. It meant that botany was not the preserve of scholars writing in Latin. On the contrary, botany was a walk in the park, a pastime for the people.

The method that Lamarck developed to win his bet was the same one he then presented to great acclaim in French Flora. He called it a “method of dissection”; today it’s called a “dichotomous key.” It works like this: You take an unknown specimen and answer a branching series of “this or that” questions; for example, does it have immediately apparent stamens and pistils or not? The answer to each question determines the next; for instance, if your specimen has immediately apparent stamens and pistils, are the florets grouped in calyxes, or are they independent? If the florets are grouped in calyxes, are the florets all the same, or are some cone shaped and others tongue shaped? If they’re all the same, are they cone shaped or tongue shaped? If they’re cone shaped, eh ben voilà! Your specimen is Carduus marianus: a milk thistle.

Apart from achieving popular success by bringing botany to the people, Lamarck’s major purpose in French Flora was to exploit what seemed to be a little opening in the field of botany in the form of a rift among botanists regarding nomenclature. The reigning system of botanical nomenclature in Europe—the system that in fact still serves as the basis for botanical and zoological classification today—was the creation of the Swedish naturalist Carl Linnaeus, whose rhapsodies on the sex lives of plants we briefly encountered during our prefatory stroll through the Garden of Plants. By the 1770s, Linnaeus had pretty much conquered Europe—all, that is, except for the King’s Garden in Paris, where Georges Buffon, the garden’s director, adamantly rejected his system as arbitrary and artificial.

Plant sex was once again at the heart of the dispute. Having learned from Vaillant to regard flowers as the sex organs of plants, Linnaeus based his system of taxonomy and nomenclature on these organs—the stamens and pistils—reasoning that since all plants had them, they would make a convenient and consistent basis for classification. But Buffon protested that a system of tidy categories based upon a single criterion belied the lush and jumbled profusion of nature. He instead championed as more holistic and therefore more natural the classification scheme of a fellow Frenchman, in fact a fellow denizen of the King’s Garden: Tournefort, the same who had brought the Remarkable Pistachio to the garden, who had maintained that its pollen was tree “excrement,” and whom a passing wagon had spared from living to witness his former student Vaillant’s announcement that the pollen was in fact tree semen.

Buffon’s opposition to Linnaeus was passionate, famous, and mutual: Linnaeus got lasting revenge by giving the name Buffonia to a marsh plant that serves to shelter toads, punning on bufo, Latin for “toad,” the extra f a nudge-wink that has propagated itself down through centuries of botanical textbooks. In this conflict, Lamarck perceived his opportunity. He would develop his own system, drawing upon both Tournefort and Linnaeus while supplanting both. Of Tournefort’s approach, with its “thousands of species” breeding confusion and tedium, Lamarck exclaimed, “What chaos!” Of Linnaeus’s, he objected, “Why neglect the multiple resources that Nature gives us to help us know her?” Lamarck promised a happy compromise between Tournefort’s chaos and Linnaeus’s reductive simplicity: a method that would be, like Little Bear’s porridge, just right.

This was one of the rare moments in Lamarck’s life when he pulled off this kind of savvy maneuver. Usually, as we’ll see, he landed on the wrong side of political machinations, or just clinging by his fingernails to professional survival. But this first time, with beginner’s luck, it worked: Buffon warmly embraced Lamarck’s project of superseding Linnaeus and arranged for French Flora to be printed by the Imprimerie Royale (the royal printer) at the government’s expense. He also appointed himself Lamarck’s patron and protector. This was a great advantage, since Buffon was a towering figure in natural history, with extensive resources and influence. With Buffon’s advocacy, Lamarck immediately gained admission as an adjunct member to the botanical section of the Royal Academy of Sciences.

In fact, the flowers were not meant to beguile humans. These “most sensitive and most universal organs” were meant to fulfill the plants’ own sex lives.

Buffon did all this, moreover, even though Lamarck not only used primarily Linnaean names in French Flora but also endorsed Linnaeus’s principle of the primacy of plant sex: the very thing, Lamarck observed, that distinguished plants from minerals as organic beings. Like other living things, plants existed in sentient and even sensuous relation to one another. The self-centered human observer, roaming admiringly amid the brilliant “greenery enameled with a thousand colors,” might well feel it was all intended just for him, these lovely flowers with their “sweet perfumes” and “innocent welcome” to their “laughing and lively” presence. But in fact, the flowers were not meant to beguile humans. These “most sensitive and most universal organs” were meant to fulfill the plants’ own sex lives.

Lamarck surely labored over these Romantic effusions. He was not someone to whom words came easily; on the contrary, he was generally a stiff, dry, awkward writer. “Lamarck’s pen,” as one contemporary expressed it, was “neither elegant nor correct.” It is a remarkable thing that Buffon adopted him anyway: Buffon, who was all graceful eloquence and wit, so facile with both pen and tongue that the mathematician and philosopher Jean d’Alembert disparagingly dubbed him the “King of Sentences”; Buffon, who famously announced to the Académie Française, on the day of his election to that august body of guardians of the French language, that “style is the man himself,” providing a slogan to generations of litterateurs and sophisticates. Perhaps he was partly mocking the academicians; if so, it was also self-mockery, and it was only partly. In fact, Buffon used his brilliance as a stylist to say something that was simultaneously both lightly ironic and also perfectly earnest. Literary style was the essence not only of the man but of the science itself. He worried about Lamarck’s lack of style and asked his friend and coauthor Louis Jean-Marie Daubenton to look over the “Preliminary Discourse” of French Flora.

Daubenton redelegated the job to his own student, the budding mineralogist René-Just Haüy, who was also a professor of humanities at the University of Paris. Haüy essentially rewrote the “Preliminary Discourse” before it went to press. Lamarck, who in later life would often express his feelings of grievance against the injustices his colleagues inflicted on him, also had a quick and keen sense of obligation. Throughout his life, both in conversation and in print, he warmly acknowledged the debt to Haüy. “I confess,” he wrote, “that the style part [of the ‘Preliminary Discourse’] is entirely his.” The body of French Flora, however, with its brilliantly enameled greenery, its laughing and lively festival of nature, and its sensitive floral organs, was Lamarck’s own.

__________________________________

Excerpted from The Power of Life: The Invention of Biology and the Revolutionary Science of Jean-Baptiste Lamarck by Jessica Riskin. Copyright © 2026 by Jessica Riskin. Excerpted by permission of Riverhead Books, an imprint of Penguin Publishing Group, a division of Penguin Random House LLC. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.