Historical overview: the evolutionary theory at the beginning
With the exception of a few creationists, biological evolution is now recognised as a well established occurrence. Such was not always the case. Some ideas about evolution may be found among ancient philosophers as well as in the works of Buffon (1749-1804, see Mayr 1982) but the first clear formalisation dates back to Lamarck (1809). Following Linné, the classification of plants and animals used morphological similarity in order to establish hierarchical taxa at various levels (e.g., genera, families, orders). The general interpretation was similarity by kind, that is, those animals looking alike, such as horses and donkeys, had been created to perform similar functions in nature. The basic idea of Lamarck was that similarity was more easily explained by a common ancestral origin. Of course, such an hypothesis, called transformism, needed a mechanism. At that time, nothing was known about heredity. It was however quite obvious that different environments and ways of life might result in large variations of phenotypes (what we call now phenotypic plasticity). Lamarck proposed that such changes, induced in parents, would be passed on to offspring, a mechanism called inheritance of acquired characters.
Some time later, Geoffroy St. Hilaire (see Piveteau 1950 and Le Guyader 1998), comparing different animal phyla, tried to establish a single plan of organisation. His comparison of the anatomy of a vertebrate and of an arthropod (a lobster) remains a well remembered example. His idea was to find homologous organs in distant phyla, an argument for a single plan of organisation, and of course for a possible evolution from a single ancestor. This ''théorie des analogues'' (homologous organs were called analogous) was fiercely fighted by Cuvier, a bright comparative anatomist, but a fixist and a creationist.
The idea of Evolution was extended three decades later by Darwin (1859). Again, nothing was precisely known about heredity, and Darwin believed in the heredity of acquired characters. His theory of gemmules, elaborated later, also turned out to be wrong. The merit of Darwin, however, was to suggest and argue for a mechanism of evolution, which is natural selection. Still now natural selection, with its multiple aspects, appears as the central mechanism of biological evolution.