Philosophie zoologique ("Zoological Philosophy, or Exposition with Regard to the Natural History of Animals") is an 1809 book by the French naturalist Jean-Baptiste Lamarck, in which he outlines his pre-Darwinian theory of evolution, part of which is now known as Lamarckism. In the book, Lamarck named two supposed laws that would enable animal species to acquire characteristics under the influence of the environment. The first law stated that use or disuse would cause body structures to grow or shrink over the generations. The second law asserted that such changes would be inherited. Those conditions together imply that species continuously change by adaptation to their environments, forming a branching series of evolutionary paths. Lamarck was largely ignored by the major French zoologist Cuvier, but he attracted much more interest abroad. The book was read carefully, but its thesis rejected, by nineteenth century scientists including the geologist Charles Lyell and the comparative anatomist Thomas Henry Huxley. Charles Darwin acknowledged Lamarck as an important zoologist, and his theory a forerunner of Darwin's evolution by natural selection.
Context
Jean-Baptiste Lamarck (1744–1829) was a member of the French Academy of Sciences and a professor of botany at the Jardin des Plantes and then became the first professor of zoology at the new Muséum national d'Histoire naturelle. He became known for his work on the taxonomy of the invertebrates, especially of molluscs. However, he is mainly remembered for the theory that now bears his name, Lamarckism, and in particular his view that the environment (called by Lamarck the conditions of life) gave rise to permanent, inherited, evolutionary changes in animals. He described his theory in his 1802 Recherches sur l'organisation des corps vivants, and in his 1809 Philosophie zoologique, and later in his Histoire naturelle des animaux sans vertèbres, (1815–1822).
Book
In the Philosophie zoologique, Lamarck proposed that species could acquire new characteristics from influences in their environment, in two rules that he named as laws. His first law stated that use or disuse of a body's structures would cause them to grow or shrink in the course of several generations. His second law held that any changes made in this way would be inherited. Together, Lamarck's laws imply the steady adaptation of animals to their environments. He gave names to a number of vestigial structures in the book, among them "Olivier's Spalax, which lives underground like the mole, and is apparently exposed to daylight even less than the mole, has altogether lost the use of sight: so that it shows nothing more than vestiges of this organ." Lamarck described speciation as follows:
as new modifications will necessarily continue to operate, however slowly, not only will there continually be found new species, new genera, and new orders, but each species will vary in some part of its structure and form ... individuals which from special causes are transported into very different situations from those where the others occur, and then constantly submitted to other influences – the former, I say, assume new forms, and then they constitute a new species. He argued that gaps between differing kinds of animals resulted from the extinction of intermediate forms, in:
a branching series, irregularly graduated which has no discontinuity in its parts, or which, at least, if it's true that there are some because of lost species, has not always had such. It follows that the species that terminate each branch of the general series are related, at least on one side, to the other neighboring species that shade into them. Lamarck proposed the transmutation of species ("transformisme"), but did not believe that all living things shared a common ancestor. Rather he believed that simple forms of life were created continuously by spontaneous generation. He also believed that an innate life force, which he sometimes described as a nervous fluid, drove species to become more complex over time, advancing up a linear ladder of complexity similar to the mediaeval great chain of being.
Contents
The first volume concerns natural history, the second physiology, and the third psychology. Page numbers are given in parentheses.
VOLUME 1 Avertissement (I–XXV) Discours Préliminaire (1)
Première Partie (Considérations sur l'Histoire naturelle des Animaux, leurs caractères, leurs rapports, leur organisation, leur distribution, leur classification et leur espèces) I. Des Parties de l'art dans les productions de la Nature (17) II. Importance des Rapports (39) III. De l'Espèce parmi les Corps vivans, et de l'idée que nous devons attacher à ce mot (53) IV. Généralités sur les Animaux (82) V. Sur l'Etat actuel de la Distribution et de la Classification des Animaux (102) VI. Dégradation et simplification de l'organisation d'une extrémité a l'autre de la Chaîne animale (130) VII. De l'influence des Circonstances sur les actions et les habitudes des Animaux, et de celle des actions et des habitudes de ces Corps vivans, comme causes qui modifient leur organisation et leurs parties (218) VIII. De l'Ordre naturel des Animaux et de la disposition qu'il faut donner a leur distribution generale pour la rendre conforme a l'ordre meme de la nature (269)
Seconde Partie (Considerations sur les Causes physiques de la Vie, les conditions qu'elle exige pour exister, la force excitatrice de ses mouvemens, les facultes qu'elle donne aux corps qui la possedent, et les resultats de son existence dans les corps)(359) Introduction (359) I. Comparison des Corps inorganiques avec les Corps vivans, suivie d'un Parallele entre les Animaux et les Vegetaux (377) II. De la Vie, de ce qui la constitue, et des Conditions essentielles a son existence dans un corps (400)
VOLUME 2 [1830 edition] III. De la cause excitatrice des mouvemens organiques (1) IV. De l'orgasme et de l'irritabilité (20) V. Du tissu cellulaire, considere comme la gangue dans laquelle toute organisation a ete formee (46) VI. Des generations directes ou spontanees (61) VII. Des resultats immediats de la vie dans un corps (91) VIII. Des facultes communes a tous les corps vivans (113) IX. Des facultes particulieres a certains corps vivans (127)
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