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The idea of a tree of life arose from ancient notions of a ladder-like progression from lower into higher forms of life (such as in the Great Chain of Being).Early representations of "branching" phylogenetic trees include a "paleontological chart" showing the geological relationships among plants and animals in the book Elementary Geology, by Edward Hitchcock (first edition: 1840).
The results are a phylogenetic tree—a diagram setting the hypothetical relationships between organisms and their evolutionary history. [4] The tips of a phylogenetic tree can be living taxa or fossils, which represent the present time or "end" of an evolutionary lineage, respectively. A phylogenetic diagram can be rooted or unrooted.
The term polyphyly, or polyphyletic, derives from the two Ancient Greek words πολύς (polús) 'many, a lot of', and φῦλον (phûlon) 'genus, species', [8] [9] and refers to the fact that a polyphyletic group includes organisms (e.g., genera, species) arising from multiple ancestral sources.
It includes the study of genetic change and the consequent variation that often results in speciation, one of the most important types of radiation into taxonomic groups called clades. A description of radiation is called a phylogeny and is often represented by type of diagram called a phylogenetic tree.
The molecular trees are mapped in relation to paleogeographic history of the region for a complete phylogeographic study. The tree shown in the center of the figure has its branch lengths calibrated to a molecular clock, with the geological time bar shown at the bottom. The same phylogenetic tree is duplicated four more times to show where each ...
A comparison of phylogenetic and phenetic (character-based) concepts. Systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees (synonyms: phylogenetic trees, phylogenies).
The science that tries to reconstruct phylogenetic trees and thus discover clades is called phylogenetics or cladistics, the latter term coined by Ernst Mayr (1965), derived from "clade". The results of phylogenetic/cladistic analyses are tree-shaped diagrams called cladograms ; they, and all their branches, are phylogenetic hypotheses.
The principle of phylogenetic reconciliation was introduced in 1979 [14] to account for differences between genes and species-level phylogenies. In a parsimonious setting, two evolutionary events, gene duplication and gene loss were invoked to explain the discrepancies between a gene tree and a species tree.