Inheritance of acquired characters: the second law of the 'Philosophie zoologique'
A rule that changes acquired by an individual during its life through circumstances and through use or disuse of an organ are transmitted to offspring, provided the changes are common to both parents.
This rule is the second law of the 'Philosophie zoologique' (1809) of the Frenchman Jean-Baptiste Lamarck. According to Burkhardt, Lamarck did not regard the inheritance of acquired characters as his own discovery: he took it as an obvious truth needing neither facts nor experiment, and took pride in other things, the idea that nature produced all forms of life successively and the role of habit in the change of species.
It was this law that became both banner and target: Darwin leaned on it in explaining heredity, and the German August Weismann in the 1880s declared that without it 'the Lamarckian theory completely collapses'. No mechanism carrying what the body acquires into the germ cells was found; whether epigenetics has reopened the question is still argued.
Why this date
High for the year. The 'Philosophie zoologique' appeared in Paris in August 1809 (Burkhardt, Genetics 194, 2013); the two laws are printed in chapter VII of part one, page 235 of the first edition (as cited by Burkhardt). The notion that what parents acquire passes to their children is much older and, in Burkhardt's words, was a commonplace for Lamarck, so the date marks not the origin of the idea but its first formulation as a law of heredity inside an evolutionary theory.
What grew out of it
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Pangenesis: gemmules from the whole body gather in the germ cells
influenced · Confidence: medium
Pangenesis was built so as to explain, among other things, the inheritance of the acquired: a cell altered by conditions or by use throws off altered gemmules. Lamarck's law entered the list of facts that Darwin's hypothesis undertook to connect.
Dispute: The confidence is deliberately lowered. Historians agree that pangenesis explained the inheritance of acquired characters, but not that Darwin took this from Lamarck in particular: Burkhardt insists that for Lamarck and his contemporaries this was a commonplace rather than Lamarck's 'signature' idea, and that Darwin held it in his own right from the time of the Origin. Cowan traces the line through Buffon and Erasmus Darwin. The link runs from the doctrine first written down as a law in 1809 to the hypothesis that undertook to explain it, not from book to book.
Link sources
- Ruth Schwartz Cowan, Commentary: Before Weismann and germplasm there was Galton and eugenics, International Journal of Epidemiology 45 (1), 15-20 (2016) Verified 20 Sep 2026
Quite explicitly, pangenesis allowed for and explained how acquired characters could be inherited.
- Richard W. Burkhardt, Lamarck, Evolution, and the Inheritance of Acquired Characters, Genetics 194 (4), 793-805 (2013) Verified 20 Sep 2026
Nine years later in his Variation of Animals and Plants Under Domestication, Darwin offered his “provisional hypothesis of pangenesis” to account for a whole range of phenomena related to heredity and development, including the inheritance of acquired characters (Darwin 1868).
- Yongsheng Liu, Qi Chen, 150 years of Darwin's theory of intercellular flow of hereditary information, Nature Reviews Molecular Cell Biology 19 (12), 749-750 (2018) Verified 20 Sep 2026
Importantly, Darwin proposed that the environment could modify gemmules, and thus that the composition of gemmules mirrors the organism’s environmental exposure.
"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.
- Ruth Schwartz Cowan, Commentary: Before Weismann and germplasm there was Galton and eugenics, International Journal of Epidemiology 45 (1), 15-20 (2016) Verified 20 Sep 2026
Other links
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'Das Keimplasma': the continuity of the germ plasm and the mouse-tail experiment
refuted by · Confidence: high
Weismann declared that acquired characters are not inherited because changes of the body do not reach the germ plasm; in 1887-1888 he cut off the tails of white mice over several generations and obtained not one tailless young. He himself wrote that without the transmission of the acquired 'the Lamarckian theory completely collapses'.
Dispute: The refutation is not held to be final by everyone. First, the mouse experiment tests only the inheritance of mutilations, not of the effects of use and disuse that Lamarck spoke of; Gauthier pointed this out (BIOS 61, 1990, as summarised in the English Wikipedia, the article itself was not read). Second, Weismann himself granted that Darwin 'to a large extent retained' the Lamarckian principle, so the blow fell on Darwin too. Third, since the 2000s epigenetic inheritance has been presented as a confirmation 'at least of a sort' of Lamarck's most famous idea; Burkhardt (2013) writes plainly that he does not take the modern studies as a vindication of Lamarck, yet grants that the argument is open. What is marked as a dead end here is the mechanism that was not found: the direct carrying of a character acquired by the body into the offspring through the use of an organ; the question of non-genetic transmission through epigenetic marks remains separate and alive.
Link sources
- Ruth Schwartz Cowan, Commentary: Before Weismann and germplasm there was Galton and eugenics, International Journal of Epidemiology 45 (1), 15-20 (2016) Verified 20 Sep 2026
Weismann, one of the ablest of the German founders of cytology, is famous for having given the inheritance of acquired characters its final coup de grace by cutting off the tails of newborn laboratory mice and observing their offspring for several generations without once finding a newborn tail-less mouse.
- Gloria Robinson, «Weismann, August Friedrich Leopold», Complete Dictionary of Scientific Biography (2008) Verified 5 Oct 2026
He followed the results of mutilations, cutting off the tails of hundreds of mice, but without any apparent hereditary effects.
- Gloria Robinson, «Weismann, August Friedrich Leopold», Complete Dictionary of Scientific Biography (2008) Verified 20 Sep 2026
He decided that acquired characters could not be inherted, for to become inheritable, changes would have to affect the germ plasm itself.
- August Weismann, On the Supposed Botanical Proofs of the Transmission of Acquired Characters (1888), Essays upon Heredity and Kindred Biological Problems, Oxford: Clarendon Press, 1889 (1889) Verified 5 Oct 2026
For if acquired characters cannot be transmitted, the Lamarckian theory completely collapses, and we must entirely abandon the principle by which alone Lamarck sought to explain the transformation of species,
"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.
- Ruth Schwartz Cowan, Commentary: Before Weismann and germplasm there was Galton and eugenics, International Journal of Epidemiology 45 (1), 15-20 (2016) Verified 20 Sep 2026
Node sources
- J.-B. Lamarck, Philosophie zoologique, Paris: Dentu, 1809, t. 1, ch. VII (1809) Verified 5 Oct 2026
DEUXIÈME LOI. Tout ce que la nature a fait acquérir ou perdre aux individus par l’influence des circonstances où leur race se trouve depuis long-temps exposée, et, par conséquent, par l’influence de l’emploi prédominant de tel organe, ou par celle d’un défaut constant d’usage de telle partie ; elle le conserve par la génération aux nouveaux individus qui en proviennent, pourvu que les changemens acquis soient communs aux deux sexes, ou à ceux qui ont produit ces nouveaux individus.
- Richard W. Burkhardt, Lamarck, Evolution, and the Inheritance of Acquired Characters, Genetics 194 (4), 793-805 (2013) Verified 5 Oct 2026
In 1809, in his now famous Philosophie zoologique, Lamarck set out this idea more systematically in the form of two laws
- Richard W. Burkhardt, Lamarck, Evolution, and the Inheritance of Acquired Characters, Genetics 194 (4), 793-805 (2013) Verified 5 Oct 2026
Certainly he did not claim the idea as his own. Instead, he treated it as commonplace, which it was. He believed it was so transparently obvious that it needed no assemblage of facts or trial by experiment to confirm it.
- Richard W. Burkhardt, Lamarck, Evolution, and the Inheritance of Acquired Characters, Genetics 194 (4), 793-805 (2013) Verified 5 Oct 2026
His observations on a live seal brought to the Museum of Natural History at the end of June 1809 were the occasion for him to append some last-minute “additions” to his Philosophie zoologique before it appeared in print (in August 1809).
- Ruth Schwartz Cowan, Commentary: Before Weismann and germplasm there was Galton and eugenics, International Journal of Epidemiology 45 (1), 15-20 (2016) Verified 5 Oct 2026
Subsequently, Buffon's famous disciple Jean Baptiste Lamarck, whose major work Philosophie Zoologique appeared in 1809, followed Erasmus Darwin in turning his mentor's vision on its head, seeing evolution as progressive rather than retrogressive, going from simplicity to complexity while retaining the same proposed mechanism, a ‘life force’ which allowed organisms to pass on traits that they had acquired (in response to changing environmental circumstances) during their lifetimes.
- August Weismann, On the Supposed Botanical Proofs of the Transmission of Acquired Characters (1888), Essays upon Heredity and Kindred Biological Problems, Oxford: Clarendon Press, 1889 (1889) Verified 5 Oct 2026
For if acquired characters cannot be transmitted, the Lamarckian theory completely collapses, and we must entirely abandon the principle by which alone Lamarck sought to explain the transformation of species,
"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.