Lamarck to Darwin : contributions to evolutionary biology, 1809-1859 / [edited by Henry Lewis McKinney].

Date:
1971
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Lamarck to Darwin : contributions to evolutionary biology, 1809-1859 / [edited by Henry Lewis McKinney]. Source: Wellcome Collection.

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    10 Lamarck (1809) them to new actions which have become habitual — the result will be the use of such parts that are preferred to others, and in certain cases, the total neglect [lack of use] of a part which has become useless. None of this should be considered as hypothesis or personal opinion; on the contrary, these are truths which require only attention to and observation of the facts in order to be rendered evident. By citing well-known substantiating facts, we shall see presently that, on the one hand, new needs — having made a part necessary — really have given birth to that part by virtue of repeated efforts; and that subsequently its constant use gradually has strengthened, devel¬ oped, and finally enlarged it considerably. On the other hand, we shall see that in certain cases the new circumstances and new needs, having made a part completely useless, the total neglect of that part has resulted in its gradually ceasing to share in the development in which the other parts of the animal do share; that it gradually shrinks and diminishes; and that when there has been complete neglect for a long time, the part in question eventually disappears. All this is fact, for which I propose to give the most convincing proofs. In plants, where there are no activities [such as those of animals] and consequently no habits per se, great alterations of environmental circumstances nonetheless lead to great differences in the development of their parts; so that these differences produce and develop some of them, while they reduce and cause the disappearance of others. But all this is brought about by the changes occurring in the nutrition of the plant, in its absorption and transpiration, in the quantity of heat [calorique], light, air, and humidity which it habitually receives; finally, in the superiority that certain of the different vital movements may assume over others. Among individuals of the same species, some of which are constantly well nourished and in circumstances favorable to their development, while others live in exactly reversed circumstances, a difference arises in the condition of these individuals which gradually becomes very noticeable. How many examples I might cite in animals and plants which would confirm the grounds for this view! Now, if the circumstances remain the same, making habitual and constant the condition of individuals poorly nourished, injured or sickly, their internal organization eventually is modified, and reproduction between them preserves the acquired modifications, giving rise ultimately to a race very distinct from those found in circumstances which are always favorable to their development.
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