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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    Influence of Circumstances 15 2. Every change in the needs of animals necessitates different actions to satisfy the new needs and, consequently, different habits. 3. Every new need, necessitating new actions to satisfy it, requires of the animal that it either [a] use certain parts more frequently than it did before, thereby considerably developing and enlarging them, or [b] use new parts which their [new] needs have imperceptibly developed in them, by virtue of the operations of their own inner sense \par des efforts de son sentiment intérieur]. I shall prove this shortly by known facts. Therefore, to obtain a knowledge of the true causes of so many diverse forms and so many different habits of which [commonly] known animals offer us examples, we must consider that the infinitely diversified, but always slowly changing circumstances in which the animals are successively found, have introduced each of them to new needs and, of necessity, to changes in their habits. Now, this cannot be denied once it is recognized. We shall easily perceive how new needs may have been satisfied and new habits adopted, if we pay attention to the following two laws of nature, which observation always verifies: FIRST LAW In every animal which has not yet passed beyond the limit /terme/ of its development, the more frequent and sustained use of any organ gradually strengthens, develops and enlarges that organ, and gives it a strength proportional to the length of time it has been used; while the constant disuse of such an organ imperceptibly weakens and deter¬ iorates it, progressively diminishing its faculties, until it finally disappears. SECOND LAW Everything which nature has caused individuals to acquire or lose as a result of the influence of environmental conditions to which their race has been exposed over a long period of time - and consequently, as a result of the effects caused either by the extended use (or disuse) of a particular organ - [all this] is conveyed by generation to new individuals descending therefrom, provided that the changes acquired are common to both sexes, or to those which have produced the new individmls.
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