Hidrogeno

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  • Publicado : 30 de noviembre de 2010
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Introduction
Darwin’s ideas about descent with modification have given rise to the study of phylogeny, or evolutionary relationships among organisms. Biologists now group organisms into categories that represent lines of evolutionary descent, or phylogeny, not just physical similarities. The strategy of grouping organisms together based on their evolutionary history is called evolutionaryclassification.

Not only is phylogeny important for understanding paleontology, but paleontology in turn contributes to phylogeny. Many groups of organisms are now extinct, and without their fossils we would not have as clear a picture of how modern life is interrelated. We express the relationships among groups of organisms through diagrams called cladograms, which are like genealogies of species.In fact, phylogeny is the evolutionary history of a species or taxonomic group. Consequently, cladistics represents a phylogenetic classification system that uses shared derived characters and ancestry as the sole criterion for group taxa. Meaning that cladistics is a method or way to unite systematic with phylogenetics. A clade is a set of groups that are related by descent from a singleancestral lineage.

Phylogenetics
In biology, phylogenetics is the study of evolutionary relatedness among various groups of organisms (for example, species or populations), which is discovered through molecular sequencing data and morphological data matrices. The term phylogenetics is of Greek origin from the terms phyle/phylon, meaning "tribe, race", and genetikos, meaning "relative to birth" fromgenesis ("birth"). Taxonomy, the classification, identification, and naming of organisms, has been richly informed by phylogenetics but remains methodologically and logically distinct.
The fields overlap however in the science of phylogenetic systematics – often called “cladism” or “cladistics” – where only phylogenetic trees are used to delimit taxa, which represent groups of lineage-connectedindividuals. In biological systematics as a whole, phylogenetic analyses have become essential in researching the evolutionary tree of life.

Phylogenetics Systematics
Carolus Linnaeus was also credited with pioneering systematics, the field of science dealing with the diversity of life and the relationship between life's components. Systematics reaches beyond taxonomy to elucidate new methodsand theories that can be used to classify species based on similarity of traits and possible mechanisms of evolution, a change in the gene pool of a population over time.
Phylogenetic systematics is that field of biology that does deal with identifying and understanding the evolutionary relationships among the many different kinds of life on earth, both living (extant) and dead (extinct).Evolutionary theory states that similarity among individuals or species is attributable to common descent, or inheritance from a common ancestor. Thus, the relationships established by phylogenetic systematics often describe a species' evolutionary history and, hence, its phylogeny, the historical relationships among lineages or organisms or their parts, such as their genes.

History of PhylogeneticsCharles Darwin was the first to recognize that the systematic hierarchy represented a rough approximation of evolutionary history. However, it was not until the 1950s that the German entomologist Willi Hennig proposed that systematics should reflect the known evolutionary history of lineages as closely as possible, an approach he called phylogenetic systematics. The followers of Hennig weredisparagingly referred to as "cladists" by his opponents, because of the emphasis on recognizing only monophyletic groups, a group plus all of its descendents, or clades. However, the cladists quickly adopted that term as a helpful label, and nowadays, cladistic approaches to systematics are used routinely.
Construction of a phylogenetic tree
Evolution is regarded as a branching process, whereby...
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