Ernst Hackel (1866) introduced the method of representing phylogeny by means of trees or branching diagrams. Third period was characterized by study of evolution within species. During this period, the foundation for establishment of population genetics was proposed.
Taxonomy provides a picture of existing biodiversity on earth along with information needed for entire biology. It provides most information needed for reconstruction of phylogeny of life and ordering systems or classification.
It also reveals numerous interesting evolutionary phenomenons and makes them available for casual study. Taxonomy is divided into micro-taxonomy and macro-taxonomy.
Discrimination of species is referred to as micro-taxonomy. Classification of organisms above the species level is called macro-taxonomy. There are three levels of taxonomy. Alpha taxonomy deals with characterization and naming of species.
Beta taxonomy deals with arranging of species into a natural system of lower and upper taxa. Gamma taxonomy deals various biological aspects of taxa, ranging from study of intra-specific population to studies of speciation and of evolutionary rates and trends.