Comparative anatomy

Comparative anatomy is the study of the evolution of species through similarities and differences in their anatomy. In other words: the study of the morphology, function, origin, similarities, and homologies of the organs and systems of different animals.

Through the analysis of anatomo-functional similarities and differences, it aims to classify animal forms into related groups, to arrive at a more complete understanding of the laws governing their organization, and to reconstruct the history of their evolution. Under certain circumstances, in order to document the continuity of an evolutionary process, it is appropriate to compare living forms with extinct ones. Observations in this area can be found in the works of Aristotle, who used anatomo-comparative criteria to classify animals.

In the Renaissance, with the birth of the great anatomical schools, dissections of human and animal cadavers provided the occasion for important comparative considerations. Examples include Leonardo da Vinci, who compared the skeleton of the wing of birds with that of the upper limb of man; Fabrici d’Acquapendente, whose De formatu foeti described the morphology of the fetus in a large number of animals, thus laying the foundations of comparative embryology; and M. A. Severinus (1580-1656), who in his Zootomia Democritea dealt with the anatomy of mammals, birds, insects, and other invertebrates, and proposed the theory of the existence of a single level of organization in all animal organisms. The discovery of the microscope and the observations made with this instrument by M. Malpighi, J. Swammerdam and others gave further impetus to the study of this subject.

However, the comparative anatomical study of the organs as a scientific discipline in its own right was concretized at the beginning of the nineteenth century, when the lectures of G. Cuvier (1769-1832) entitled: D’anatomie comparée, the first written work in which the similarities and differences of the organs of many animals, mainly vertebrates, were methodically presented. At that time, the teaching of comparative anatomy and the field of its research were dominated by the concept of J. W. Goethe’s (1749-1832) Urtypus, according to which the morphologist’s most important research tool is the comparative method and its goal is the search for an “ideal type” to which the various animal forms can be traced, disregarding the less important anatomical peculiarities.

Later, K. Gegenbaur (1826-1903) and his school, as a result of currents inspired by the studies of G. L. Buffon (1707-1788), E. L. Geoffroy Saint-Hilaire (1772-1844), J. B. Lamarck (1744-1829) and especially the theory of natural evolution of C. Darwin (1809-1882) and A. R. Wallace (1823-1913), put evolution before function as an interpretive criterion to explain the organological transformations that occurred over millennia from one form to another. Until the advent of experimental sciences in the first decades of the 20th century, the means of study were exclusively direct, that is, limited to comparative macroscopic and microscopic anatomical analysis. The same methods were used to study teratological forms, which, when studied comparatively, provide important elements for the morphological interpretation of organs. Among the indirect methods subsequently used, the most important is that of experimental embryology, developed by W. Roux and H. Spemann, which consists in attempting to discover the causes of form by experimentally interfering with development by mechanical means, hormonal substances, chemicals, etc. In addition to experimental embryology, there is also the study of teratological forms, which provide important elements for the morphological interpretation of organs.

In addition to experimental embryology, biochemical genetics, based on the analysis of homologous proteins (especially isoenzymes) extracted from different individuals, proved particularly useful. Since the time of its founders, the study of comparative anatomy has been devoted mainly to vertebrates, although a general treatment was attempted by, among others, A. Lang (1855-1914), O. Bütschli (1848-1920) and L. Plate (1862-1937). Ultimately, however, the unified study of the comparative anatomy of all animals is not considered possible. In fact, the anatomy of invertebrates presents a variety of levels of organization that cannot be framed in a separate organic doctrine and is therefore treated as zoology.

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