The second component of Lamarck's theory of evolution was the adaptation of organisms to their environment. This could move organisms sideways from the ladder of progress into new and distinct forms with local adaptations. It could also drive organisms into evolutionary blind alleys, where the organism became so finely adapted that no further change could occur. This was later expanded in Charles Darwin's theories of species adaptation and natural selection.

Lamarck argued that this adaptive force was powered by the interaction of organisms with their environment, by the use and disuse of characters:

In every animal which has not passed the limit of its development, a more frequent and continuous use of any organ gradually strengthens, develops and enlarges that organ, and gives it a power proportional to the length of time it has been so used; while the permanent disuse of any organ imperceptibly weakens and deteriorates it, and progressively diminishes its functional capacity, until it finally disappears.

These characters were then inherited, according to the common belief of the day, in what is known as "soft inheritance" (nowadays erroneously called Lamarckism):

All the acquisitions or losses wrought by nature on individuals, through the influence of the environment in which their race has long been placed, and hence through the influence of the predominant use or permanent disuse of any organ; all these are preserved by reproduction to the new individuals which arise, provided that the acquired modifications are common to both sexes, or at least to the individuals which produce the young.

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Legacy

Statue of Lamarck in the Jardin des Plantes, Paris. The inscription reads, "Fondateur de la doctrine de l'évolution" (Founder of the doctrine of evolution)

Lamarck constructed what may be the first comprehensive theoretical framework of organic evolution. Stephen Jay Gould argues that Lamarck was the "primary evolutionary theorist", in that his ideas and the way in which he structured his theory set the tone for much of the subsequent thinking in evolutionary biology, through to the present day.^[27]

Lamarck is usually remembered for his belief in the inheritance of acquired characteristics, and the "use and disuse" model by which organisms developed their characteristics. Lamarck incorporated this belief into his theory of evolution, along with other more common beliefs of the time, such as spontaneous generation.

The inheritance of acquired characteristics (also called the theory of adaptation or "soft inheritance") was rejected by August Weismann when he developed a theory of inheritance in which "germ-plasm" (the hereditary material passed from parents to offspring) remained separate and distinct from "soma" (the material composing the body of an organism); thus nothing which happens to the soma may be passed on with the germ-plasm. This model underlies the modern understanding of inheritance. Weismann is famous for an experiment in which he cut the tails off mice, demonstrating that the injury was not passed on to the offspring; but historians of science such as Stephen Jay Gould argue that this experiment had far less effect on the acceptance of Lamarckism than Weismann's more comprehensive theoretical framework^[27] (Believers in Lamarckian inheritance did not count injury or mutilation as a true acquired characteristic: only those which were initiated by the animal's own needs, that were beneficial, were expected to be passed on. This Lamarckian view is consistent with Charles Darwin's theory of natural selection).

Lamarckism is used as an analogy to describe the action of other "evolutionary" concepts in the modern era. For example, the memetic theory of cultural evolution is sometimes described as a form of "Lamarckian" inheritance of non-genetic traits.

The honeybee subspecies Apis mellifera lamarckii is named after Lamarck. Likewise, the bluefire jellyfish (Cyaneia lamarckii) has been named after him.

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See also

• Lamarckism
• Acclimation
• Exaptation
• Evolution
• Gene-centered view of evolution
• Intragenomic conflict
• Lysenkoism
• Maladaptation
• Neutral theory of molecular evolution
• Phenotypic plasticity
• Preadaptation
• Spandrel

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Major Works

Lamarck's writings are available in facsimile and in word format (fr) at www.lamarck.cnrs.fr. Search engine allows full text search.

• 1809. Philosophie zoologique, ou Exposition des considérations relatives à l’histoire naturelle des animaux..., Paris.

On invertebrate classification:

• 1801. Système des animaux sans vertèbres, ou tableau général des classes, des ordres et des genres de ces animaux; présentant leurs caractères essentiels et leur distribution, d'après la considération de leurs..., Paris, Detreville, VIII : 1-432.
• 1815-1822. Histoire naturelle des animaux sans vertèbres, présentant les caractères généraux et particuliers de ces animaux..., Tome 1 (1815): 1-462; Tome 2 (1816): 1-568; Tome 3 (1816): 1-586; Tome 4 (1817): 1-603; Tome 5 (1818): 1-612; Tome 6, Pt.1 (1819): 1-343; Tome 6, Pt.2 (1822): 1-252; Tome 7 (1822): 1-711.

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References

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External links

Find more about Jean-Baptiste Lamarck on Wikipedia's sister projects:
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• The Imaginary Lamarck: A Look at Bogus "History" in Schoolbooks by Michael Ghiselin
• Epigenetics: Genome, Meet Your Environment
• Science Revolution Followers of Lamark
• A. P. Packard. Lamarck, the Founder of Evolution, His Life and Work, available at Project Gutenberg.
• Jean-Baptiste Lamarck: works and heritage, online materials about Lamarck (herbarium, manuscripts, books, etc.) edited online by Pietro Corsi (Oxford University) and realised by CRHST-CNRS in France.
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