Homology Is A Central Concept Within The Field Of...

Homology is a central concept within the field of phylogenetics. It represents the idea of similarity in structure or anatomical position between organisms, indicating a common origin. Homology is traditionally contrasted with analogy; the similarity of function in two structures that have contrasting origins. However, it is now more common for the concept to be contrasted against homoplasy; a character shared by a set of species that their common ancestor does not possess. The concept of homology was introduced in the early 19th century, before the Darwinian evolutionary theory was formulated. Two main criteria were used until the first half of the 20th century, in order to establish homologies between species. 1. The positional criterion. This outlines that the relative configuration and position of homologous structures must be maintained between the different species that possess them. 2. The embryological criterion. This is the assumption that the identical developmental precursors are used to develop homologous structures in individuals of different species. Development in the phylogenetics field in the second half of the 20th century included the introduction of molecular phylogeny and evolution. These additions strongly enhanced the concept of homology. In addition, it was found that homologous structures can develop from non-homologous development precursors. This caused the embryological criterion to fail, and so new outlines needed to be established in order