Hormones and Heredity | Page 9

J.T. Cunningham
sens que j'attache �� ces expressions: Les circonstances influent sur la forme et l'organisation des animaux, c'est-��-dire qu'en devenant tr��s diff��rentes elles changent avec le temps et cette forme et l'organisation elle-m��me par des modifications proportionn��es.
'Assur��ment si l'on prenait ces expressions �� la lettre, on m'attribuerait une erreur; car quelles que puissent ��tre les circonstances elles n'op��rent directement sur la forme et sur l'organisation des animaux aucune modification quelconque. Mais de grands changements dans les circonstances am��nent pour les animaux de grands changements dans leurs besoins et de pareils changements dans les besoins en am��nent n��cessairement dans les actions. Or, si les nouveaux besoins deviennent constants ou tr��s durables, les animaux prennent alors de nouvelles habitudes qui sont aussi durables que les besoins qui les ont fait na?tre. Il en sera r��sult�� l'emploi de telle partie par pr��f��rence �� celui de telle autre, et dans certains cas le d��faut total d'emploi de telle partie qui est devenue inutile.'
The supposed effect of these changes of habit is definitely stated in the form of two 'laws':--
PREMI��RE LOI
'Dans tout animal qui n'a point d��pass�� le terme de ses d��veloppements l'emploi plus fr��quent et soutenu d'un organe quelconque, fortifie peu �� peu cet organe, le d��veloppe, l'agrandit et lui donne une puissance proportion��e �� la dur��e de cet emploi; tandis que le d��faut constant d'usage de tel organe Paffaiblit insensiblement, le d��t��riore, diminue progressivement ses facult��s, et finit par le faire dispara?tre.
DEUXI��ME LOI
'Tout ce que la nature a fait acqu��rir ou perdre aux individus par l'influence des circonstances ou leur race se trouve depuis longtemps expos��e, et par cons��quent, par l'influence de l'emploi pr��dominant de tel organe, ou par celle d'un d��faut constant d'usage de telle partie, elle le conserve par la g��n��ration aux nouveaux individus qui en proviennent, pourvu que les changements acquis soient communs aux deux sexes, ou �� ceux qui ont produits ces nouveaux individus.'
It will be seen that this last condition excludes the question of the origin of organs or characters confined to one sex, or secondary sexual characters. With regard to the expression 'emploi de telle partie,' the explanation which Lamarck gives of the evolution of horns and antlers is curious. He does not attempt to show how the use or employment of the head leads to the development of these outgrowths of bone and epidermic horn, but attributes their development in stags and bulls to an 'interior sentiment in their fits of anger, which directs the fluids more strongly towards that part of their head.'
Lamarck's actual words (_Phil. Zool.,_ edit. 1873, p. 254) are: 'Dans leurs acc��s de coli��re qui sont fr��quents surtout entre les males, leur sentiment int��rieurs par ses efforts dirige plus fortement les fluides vers cette partie de leur tete, et il s'y fait une secr��tion de mati��re corn��e dans les uns (_Bovidae_) et de mati��re osseuse m��lang��e de mati��re corn��e dans les autres (_Cervidae_), qui donne lieu �� des protub��rances solides: de l�� l'origine des cornes, et des bois, dont la plupart de ces animaux ont la t��te arm��e.'
Darwin, on the other hand, definitely set before himself the problem of the origin of species, which the majority of naturalists, in spite of Lamarck and his predecessor Buffon, regarded as permanent and essentially immutable types established by the Creator at the beginning of the world. This principle of the persistence and fundamentally unchangeable nature of species was regarded as an article of religion, following necessarily from the divine inspiration of the Bible. This theological aspect of the subject is sufficiently curious when we consider it in relation to the history of biological knowledge, for Linnaeus at the beginning of the eighteenth century was the first naturalist who made a systematic attempt to define and classify the species of the whole organic world, and there are few species of which the limits and definition have not been altered since his time. In fact, at the present time there are very numerous groups, both in animals and plants, on the species of which scarcely any two experts are agreed.
In many cases a Linnaean species has been split up till it became, first, a genus, then a family, and, in some cases, an order. What one naturalist considers a species is considered by another a genus containing several species, and, vice versa, the species of one authority is described as merely a variety by another. The older naturalists might have said with truth: we do not know what the species are, but we are quite certain that whatever they are they have never undergone any change in their distinguishing characters. At the same time we know that whether we call related forms varieties or species or genera in different cases, we find, whatever organisms we study, whether plants or animals, definite types distinguished by special characters of form,
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