An evolution tree (or phylogenetic tree) is a visual tool used to display the inferred evolutionary relationships among various organisms. These trees have been developed by scientists as a result of studying the similarities and differences between the genetics of a species. They act as a tool in many procedures, such as testing hypotheses about evolution, examining the characteristics of different lineages, and classifying organisms. The leaves of the tree represent the most recent species while progressing towards the bottom goes further into the past.
Clade: A group of species that includes a common ancestor and all of the descendents (both extinct and living) of that ancestor.
Node: A branching point in the tree representing the last common ancestor of one or more species.
Leaf: The terminal nodes (species with no descendants).
Root: The ancestor of all of the branching descendants present in the tree (base node). Note: not all evolution trees have a root node.
Branch: The connection between two nodes (also called an edge).
Click the radio button next to a term to see an example in the evolution tree below.
Prior to scientific study of evolution and species ancestry, living things were grouped according to the Linnaean system of classification that followed the hierarchy of: kingdom, phylum, class, order, family, genus, and species. It was based purely on the physical and macroscopic descriptions of an organism. However, based on modern understanding of genetics, scientists have developed an alternative approach for classifying species on evolution trees. This type of classification is called phylogenetic classification. Phylogenetic classification only classifies species by clades (that is, groups of organisms that are descendants of a common ancestor). For example, in a Linnaean system, birds and non-avian dinosaurs may be placed into two separate groups while in a phylogenetic classification, they both belong to the same group as they are from the same lineage.
The following example considers reptiles and birds. It is important to note that 'reptiles' would not be a correct phylogenetic classification, as this classification would exclude birds.
Click the boxes to see which species are grouped in the following phylogenetic classifications.
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