Abstract

“From the first dawn of life, all organic beings are found to resemble each other in descending degrees, so that they can be classed in groups under groups.” This is the first sentence of the 13th chapter of The Origin of Species (1859). Darwin’s objective was to stress that a natural system of classification, both for plants and animals, must be based on embryology, as well as on adult morphology. To support his ideas, he first discusses the different ways organisms have been classified by their predecessors. For instance, classifying organisms by their affinities is easy in most groups according to him, since we can list a number of characters in common that they must show. The geographic distributionGeographicdistribution was also used, especially for birds; other naturalists extended this practice to insects and plants. For Darwin this is an illogical method, as also is the comparative value of the higher levels of taxonomy, such as families, orders, and so on; all this can be shown as arbitrary. As he called his theory “descent with modificationDescentdescent with modification,” a natural system of classification of species should be based on the affinities of what they inherited from a common ancestor; that is, a classification should be genealogical.