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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.
[10] [7] [11] They can, for example, be used to illustrate the concepts of parsimony and convergent evolution. [7] [10] Students are typically asked to construct a phylogenetic tree based on the morphological characteristics of the Caminalcules and taking into account evolutionary principles.
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.
[6] HGT is thus a potential confounding factor in inferring phylogenetic trees from the sequence of one gene. For example, if two distantly related bacteria have exchanged a gene, a phylogenetic tree including those species will show them to be closely related even though most other genes have diverged substantially. For this reason it is ...
Homoplasy, especially the type that occurs in more closely related phylogenetic groups, can make phylogenetic analysis more challenging. Phylogenetic trees are often selected by means of parsimony analysis. [21] [22] These analyses can be done with phenotypic characters, as well as DNA sequences. [23]
The study of plant evolution attempts to explain how the present diversity of plants arose over geologic time. 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 tree of life, like this one from Charles Darwin's notebooks c. July 1837, implies a single common ancestor at its root (labelled "1"). A phylogenetic tree directly portrays the idea of evolution by descent from a single ancestor. [3] An early tree of life was sketched by Jean-Baptiste Lamarck in his Philosophie zoologique in 1809.