History of the evolution of a species or group, especially lines of descent and relationships among broad groups. The fundamental proposition is that plants or animals of different species descended from common ancestors. Because the evidence for such relationships is almost always incomplete, most judgments of phylogenicity are based on indirect evidence and cautious speculation. Modern taxonomy, the science of classifying organisms, is based on phylogeny. Early taxonomic systems had no theoretical basis; organisms were grouped according to apparent similarity. Biologists who propose a phylogeny obtain evidence from the fields of paleontology, comparative anatomy, comparative embryology, biochemistry, and molecular biology. The data and conclusions of phylogeny indicate that today's living creatures are the product of a historical process of evolution and that degrees of resemblance within and between groups correspond to degrees of relationship by descent from common ancestors. See also phylogenetic tree.

This entry comes from Encyclopædia Britannica Concise.
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