Cladistics

Cladistics classifies organisms into groups defined by shared derived traits inherited from a common ancestor. Its branching diagrams represent hypotheses about evolutionary relationships.

Clade: A group consisting of an ancestor and all its descendants. Cladistics aims to identify groups that include complete branches of ancestry.
Common Descent: The evolutionary principle that organisms descend from shared ancestors. Cladistic relationships are hypotheses about patterns of common ancestry.
Phenetics: A classification approach that groups organisms by overall measured similarity. Unlike cladistics, phenetics does not make common ancestry the defining basis of groups.
Willi Hennig: A German entomologist who developed phylogenetic systematics into a formal method of classification. His work established the principles later widely known as cladistics.
Synapomorphy: A shared derived character inherited from a group's most recent common ancestor. These shared derived traits provide the principal evidence for grouping taxa.
Homology: Similarity between traits due to inheritance from a common ancestor. Homology helps distinguish inherited similarities from independent resemblance.
Evolutionary Taxonomy: A classification approach that considers ancestry alongside overall difference and evolutionary grade. It may retain groups that cladistics excludes for leaving out some descendants.
Phylogenetic Systematics: A systematic approach that classifies organisms according to their evolutionary relationships. Cladistics is commonly treated as the analytical core of phylogenetic systematics.
Outgroup: A taxon outside the group under study, used to infer ancestral character states. Comparing an outgroup helps distinguish derived traits from ancestral ones.
Homoplasy: Similarity between traits that did not arise from inheritance of that trait from a shared ancestor. Convergent evolution and reversals can make unrelated branches appear to share derived traits.

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