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Life on Earth
History of Systematics
"The Great Chain of Being"
The Phylogenetic Tree
Stratigraphy and phylogeny
The field of science concerned with studying and understanding of the diversification of life on the planet Earth, both past and present, and the classification of and evolutionary relationships among living things is called Systematic Biology, or Systematics for short. Systematics is concerned both with Taxonomy, the naming and classification of life, and Phylogeny, the science and study of understanding the family tree of all life on Earth. Since classification should be based, ideally, on evolutionary relationships, and since the tree of life can only be understood if we know the names of the various branches and twigs that comprise it, it follows that these two are essentially two aspects of the same field. Systematics, then is the classification of life according to its phylogenetic (evolutionary) relationships.
Phylogeny is only possible with an understanding of evolution. Before the Darwinian revolution, species were considered static, either created by God or as eternal archetypes. Examples of these earlier, static classification schemes are the Scala Naturae (Natural Ladder), the Great Chain of Being, and the original (pre-Darwinian) Linnaean system, the foundation for all nomenclature or naming of species. Today, the Linnaean system remains popular, although some systematists and vertebrate paleontologists are pushing for its abandonment in favour of a new phylogenetic classification.
Currently there are three alternative, rival but also complementary, methodologies for classifying things and mapping out the tree of life. The first is Linnaean classification as modified by the early 20th century evolutionary synthesis (this evolutionary linnaeanism was at one time called Evolutionary systematics, a term that has since fallen into disuse), paleontology, and deep time. The second is Cladistics, itself divided into several types, such as the older single tree parsimony-based approach and the newer computational statistical-based methodologies, and Molecular phylogeny. The modern science of Phylogenetics uses either or both molecular sequencing and computational cladistic methodology to construct and test synapomorphy-based hypotheses. A fourth, phenetics, is little used nowadays but contributed to the statistical and philosophical (such as the distinction between hypothesis and phylogeny) approach of modern phylogenetics. Doubtless more methodologies could be added (e.g. Systems Theory, Evo-Devo, etc). Each methodology and sub-branch thereof claims to be the true one, either accepting the others as subordinates (e.g. many phylogenetic workers consider morphology-based cladistics secondary to molecular phylogeny) or rejecting them as outmoded (e.g. cladistics rejects evolutionary systematics). In fact, each has a different methodology and deals with different aspects of phylogeny and systematics, so it is not a matter of contradiction but complementarity. MAK111009 130323
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