Types of comparison
Biologists distinguish analogous traits from homologous traits. Analogous traits are similar, because of convergent adaptation towards similar environmental conditions. An analysis of the fine structures of these traits, however, will show differences proving that they have been derived from different ancestral traits. The similarity is only superficial. The eyes of vertebrates and octopuses often serve as an example of analogous traits. Although they look extremely similar, superficially, analysing the fine structure reveals, for example, that the innervation of the retina is inverse in vertebrates, but not in octopuses.
Homologous traits can look similar or different, depending on the similarity or difference in environmental conditions to which they have been adapted. An analysis of their fine structure, however, will show identities proving that they have been derived from the same ancestral trait. The standard example for homologous traits are the limbs of vertebrates. Although they can look as different (divergent) as the wings of bats and birds or the legs of horses and humans, the fine structure (of bones, tendons, muscles) reveals that they have been derived from the same ancestral limb.
With this distinction, we can categorise comparisons as follows. If a comparison highlights differences in effects but does not compare the underlying causes, it will be a superficial contrast. If it highlights similarities in effects but does not compare the underlying causes, it will be a superficial analogy. If it highlights similarities in effects but also shows that these are due to the different underlying causes, it will be a deep analogy. Finally, if effects are similar or divergent, but the underlying causal machineries are identical, it will be a homology.
Categories of comparisons
| superficial analogy | deep analogy | superficial contrast | homology | |
effects | similar | similar | different | similar or divergent |
causes | -- | different | -- | identic |
Lamarck's homology
As shown in the previous post, Charles Naudin proposed that natural and artificial selection were not only superficially similar (analogous) in their effects, but also that this similarity was due to homologous causes. Alfred Wallace and Charles Darwin had not yet published and Matthew (1831. On Naval Timber and Arboriculture) had proposed a difference and conflict in the effects of of natural and artificial selection and did not explicitly compare the causal machineries of both processes (see taxonomy of comparisons below). Matthew's proposal was either a superficial contrast or an implied homology with divergent effects. That is, even as a homology, it was different from Naudin's homology of causes with similar effects. Therefore, Matthew (1831) is an unlikely source of inspiration for Naudin's proposal. But Lamarck (1809. Philosophie Zoologique) explicitly proposed a similarity of the effects of nature and culture due to homologous causes.
Ironically, the first English translation of Lamarck's Zoological Philosophy that is digitised and available online (via Archive.org, but not via books.google) is that of Hugh Elliot from 1914. Therefore, books.google will generally fail to identify Lamarck as a possible source of inspiration for English literature.
For simplicity (and sparing the reader the pleasure of my translations from French into English), I will quote from the translation of Elliot. As Lamarck did not publish later editions of his Philosopie Zoologique that could have differed from his first, taking Elliot's translation is just as well as translating from the French would have been.
The homology between nature and culture is at page 109 of Elliot's translation. The passage begins with a Buffonism:
"Those who have observed much and studied large collections, have acquired the conviction that according as changes occur in environment, situation, climate, food, habits of life, etc., corresponding changes in the animals likewise occur in size shape, proportions of the parts, colour, consistency, swiftness and skill.
What nature does in the course of long periods we do every day when we suddenly change the environment in which some species of living plant is situated."The original passage is at page 225-26 of Lamarck (1809, vol. 1):
"Ceux qui ont beaucoup observé, et qui ont consulté les grandes collections, ont pu se convaincre qu'à mesure que les circonstances d'habitation, d'exposition, de climat, de nourriture, d'habitude de vivre, etc., viennent à changer; les caractères de taille, de forme, de proportion entre les parties, de couleur, de consistance, d'agilité et d'industrie pour les animaux, changent proportionnellement.
Ce que la nature fait avec beaucoup de temps, nous le faisons tous les jours, en changeant nous-mêmes subitement, par rapport à un végétal vivant, les circonstances dans lesquelles lui et tous les individus de son espèce se rencontroient."
Conclusion
In contrast to later comparisons of natural with artificial selection, Lamarck had use-inheritance in place of selection. Charles Naudin merely recombined the strong homology claim already present in French science with the also already present idea of selection (see previous post).
