Jean Louis Marie Poiret 1755 – 1834) was an important French botanist (and clergyman) whose work on the flora of Barbary was followed by major contributions to Encyclopédie Méthodique: Botanique (1816) and Tableau encyclopedique et methodique des trois regnes de la nature: botanique (1819-1823); both in collaboration with Jean Baptiste Lamarck. Poiret would go on to serve as a professor of natural history at the École Centrale in Aisne. However, it is his Leçons de Flore published in 1819-1820, that Poiret fully reveals his evolutionist views.
Although Poiret is now a relatively obscure figure in the history of early evolutionary thought, a recent publication has claimed that Poiret was in fact not a transmutationist. This view is based on a series of historical errors that have been compounded by an erroneous citation dating back to the mid-nineteenth century. As Frederic Gerard, a formidable French evolutionist and botanist in his own right, wrote in his entry on Species in Dictionnaire universel d’Histoire naturelle (1844), “I am therefore convinced, like Lamarck, Poiret, and Geoffroy, that varieties become species, and that this is how new species are formed…” It is clear that Poiret’s contemporaries viewed him as a leading force in advocating evolutionary views.
In the second volume of Leçons de Flore, Poiret devotes an entire chapter (“Des espèces”) to the concept of species and how species might be formed. This is not surprising, given the rise of the natural system of classification and its corollary that species are fixed and immutable for all of time. Beginning in 1810s, the Swiss botanist Auguste-Pyramus de Candolle had been a leading advocate of natural systems of classification. As he wrote in Essai elementaire de geographie botanique (1820): “The whole theory of botanical geography is based on the idea we have of the origin of organized beings and the permanence of species.”
In Leçons de Flore, Poiret begins his arguments by noting that domesticated plants offer evidence of considerable variation and plentiful evidence of the creation of novel varieties. He advances what was then a commonly accepted (but incorrect) view that the notable variation in domesticated cultivars exceeds what might be found in nature, because species brought into gardens are exposed to environmental conditions that exceed what natural species experiences in nature. With a standard Lamarckian perspective on the induction of evolutionary change in organisms by altered environmental conditions, Poiret extends this logic to the wild (and even proposes transplant experiments to confirm the heritable nature of such evolutionary changes):
There are however special circumstances where plants end up naturalizing in climates or soils which are foreign to them: then it results in varieties which in the long run lose their original type, and reproduce, after many generations, endowed with these new attributes which they do not lose, and which lead to the formation of new species. It would then be desirable to be able to transfer these plants to the homeland of their ancestors, to follow successive generations, and to ascertain whether they would resume their primitive character over time.
Poiret demonstrates the power of domestication history to advance an evolutionist perspective – much as Charles Darwin would do in the first chapter (“Variation under domestication”) in On the Origin of Species. “Although it seems a little reckless, according to the most generally adopted opinion, to suggest that new species are formed in nature, it is very difficult to deny this assertion when we carefully observe what is happening every day in our gardens, where it is not uncommon to see varieties end up constantly reproducing the same by their seeds. Why wouldn’t the same thing happen in nature?” Poiret also invokes hybridism between congeneric species as possible source of new species, noting how common hybridization in gardens is, and extending this process to nature.
Poiret notes “the great revolutions that the terrestrial globe has experienced” and assumes that the Earth was originally covered by water, which over time receded and created the mountains and the plains:
With the lowering or retreat of the waters, the plains have become mountain peaks; the temperature, the exposure, the quality of the terrain have ceased to be the same; the nature of the plants must also have experienced great changes. They have imperceptibly taken on the character of the new localities: the trees have disappeared on great heights; those which could resist, such as birches, willows, etc., have become deformed, shortened, converted into small creeping shrubs, the stems of herbaceous plants, shortened or hardened into almost woody stumps, have lost their ramifications, or else they sprawled on the rocks in grassy tufts; the leaves, struck by the cold, have shrunk and hardened…
Poiret, departing from the dominant catastrophist theories of the day, is clearly a gradualist, noting that “these changes have most probably only come gradually: it was on the first side only varieties which, by supporting themselves, by reproducing constantly, had to take place among those that we have called species. I am even inclined enough to believe that there was first for each of our present genera, only one primitive species, that the others were formed in the long run by the change of localities…”
Poiret ends this extraordinary chapter on the nature of species by forecasting future evolutionary changes, as climates alter over time: “Today our Alps, the face of the vegetation, as well as the forms of the plants, would also change by the influence of a new temperature. Many, no doubt, would perish; but the species which could resist would experience in the long run, in the texture of their organs, modifications which, by making them lose their original character, would convert them for us into species.” Although there no scholarship on Poiret to date (with the exception of a recent erroneous claim that he was not an evolutionist), he deserves to be viewed as an important figure, one who was certainly recognized in France by Gerard in the 1840s, and from an historical perspective, as one of the first three individuals (along with von Buch in 1819 and Herbert in 1821) to draw heavily on plants to posit an evolutionary worldview.