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Jean-Baptiste Lamarck (1744–1829)

Lamarck set out the first comprehensive theory that species are not fixed but change into one another over long periods of time. He argued it from May 1800, in his lectures at the Muséum national d’histoire naturelle in Paris, and gave it its fullest form in Philosophie zoologique (1809). The theory had two parts: a power inherent in life that drives organisation from the simplest forms toward the more complex, and the influence of circumstances, which pulls lineages away from that graded series into the diversity actually observed. The second part is the one remembered, through its mechanism of use and disuse and the inheritance of what is acquired, and it is remembered largely in the form his opponents gave it. He was also the zoologist who put the animals without backbones in order, named them as a group, and was among the first to use the word “biology” in its modern sense.

Jean-Baptiste Pierre Antoine de Monet, chevalier de Lamarck was born on 1 August 1744 at Bazentin in Picardy, into a family of minor nobility. Intended for the Church, he studied with the Jesuits at Amiens until 1759, then joined the army in the Seven Years’ War, and was commissioned in the field; an injury ended his service. In Paris he studied medicine for some years, then turned to botany. His Flore françoise (1778), with its key of successive two-way choices, made his name, and he was elected to the Académie des sciences in 1779. He worked at the Jardin du Roi, from 1788 as keeper of the herbarium, and when the Revolution reorganised it as the Muséum in 1793 he was given the chair of the natural history of “insects and worms”. He held it for the rest of his life. He lost his sight from around 1818 and dictated his last work to his daughter Rosalie. He died in Paris on 18 December 1829.

Key concepts

The invertebrates. The chair of insects and worms covered a collection that Linnaeus had divided into only two classes. Lamarck split it into ten classes by 1809, named the whole group animaux sans vertèbres, and published its classification in the Système des animaux sans vertèbres (1801) and at length in the seven volumes of the Histoire naturelle des animaux sans vertèbres (1815–22). His contemporaries, Cuvier included, respected this work without reservation, and it is where the ordering from simple to complex that his theory depends on was worked out.

Biology as a science of the living. In Hydrogéologie (1802) and Recherches sur l’organisation des corps vivans (the same year) he used biologie for the study of what is common to living bodies as such, in the same year that Gottfried Reinhold Treviranus used the German word. Plants and animals, on this view, share properties that differ in kind from the physical and chemical, and life is one subject.

Two forces. In Lamarck’s mature account two causes shape living forms. The first is a tendency of life to complicate organisation, driven by the movement of fluids through the body and building ever more complex structures; left to itself it would produce a single ladder from the simplest animal to the most complex. The second is the influence of circumstances: as conditions change, what animals need changes, needs change their habits, and habits over many generations change their organs. This second cause breaks the ladder into a branching, irregularly graded series. The simplest forms are produced continually by spontaneous generation, so the series is always being restocked from below, and there is no single common ancestor. Species do not go extinct in his account; forms known only from fossils have changed into forms living now.

The two laws. Philosophie zoologique states the mechanism of the second force as two laws. The first: continued use of an organ strengthens it and constant disuse weakens it until it disappears. The second: what individuals acquire or lose in this way is preserved in their offspring, provided the change is common to both parents; the giraffe’s neck is among the book’s examples. The inheritance of acquired characters was not Lamarck’s invention; it was assumed widely from antiquity to the nineteenth century, as Conway Zirkle documented in 1946. What was his was the use he put it to: the engine of the transformation of species.

The tree of 1809. The additions at the end of Philosophie zoologique include a table showing the origin of the different animal groups as branching lines rather than a single chain, one of the earliest diagrams of its kind, half a century before Darwin’s.

The caricature and the record

Much of what was later said of Lamarck came from the éloge Georges Cuvier wrote as permanent secretary of the Académie, read on 26 November 1832, after Cuvier’s own death that May, and published in 1835. It praised the invertebrate work and presented the theory as a system of imagination, attributing to Lamarck the view that animals acquire organs by wanting them. Lamarck’s word was besoins, needs arising from changed circumstances, acting on habit rather than on will, and historians since Richard Burkhardt’s The Spirit of System (1977) and Pietro Corsi’s The Age of Lamarck (1988) have read the theory from his texts rather than from the éloge. The version that reached English readers came first through Lyell’s hostile summary in the second volume of the Principles of Geology (1832). Darwin’s own early verdict, in a letter to Hooker of January 1844, rejected “Lamarck nonsense of a ‘tendency to progression’ ‘adaptations from the slow willing of animals’”; from the third edition of the Origin (1861) his historical sketch credited Lamarck with “the eminent service of arousing attention to the probability of all change in the organic, as well as in the inorganic world, being the result of law, and not of miraculous interposition.”

The later history of the word “Lamarckian”, from the neo-Lamarckians to its uses in economics, technology and epigenetics, is covered under Lamarck and the inheritance of acquired characters.

Where Lamarck stops

The theory argued for transformation from the order of the collections and the principles of his system, not from observed change, and Cuvier pressed exactly that. When the animal mummies brought back from Egypt were examined in 1802, in a report Lamarck signed with Cuvier and Lacépède, the ibises of the pharaohs matched the living birds. Cuvier took this as evidence of fixity; Lamarck replied that the circumstances of Egypt had not changed either, and that the few thousand years since the birds were embalmed were far too short a time for change to show.

How much of the observed order belongs to each of the two forces, the texts leave unsettled, and the historians who read him most carefully describe this as a tension within the system rather than a worked-out division.

And the second law rests on an assumption he shared with nearly everyone and did not examine, how a change acquired by the body reaches the offspring, which is the step August Weismann’s separation of germ line from body put to the test in the 1880s.

Key works

Flore françoise (3 vols, 1778) — the French flora by dichotomous key; election to the Académie
Recherches sur les causes des principaux faits physiques (1794) — the physics and chemistry against Lavoisier
Système des animaux sans vertèbres (1801) — the invertebrate classification; the opening lecture of 1800
Hydrogéologie (1802) — the slowly changing earth; “biologie”
Recherches sur l’organisation des corps vivans (1802)
Philosophie zoologique (2 vols, 1809) — the two forces, the two laws, the branching table
Histoire naturelle des animaux sans vertèbres (7 vols, 1815–22) — the invertebrates at length, with the theory restated in its introduction