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How do cladistics and phenetics classify organisms differently?

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A nautilus mollusk with a spiral, brown-and-white striped shell and numerous white tentacles extending from its soft body, set against a dark background. — species A nautilus (*Nautilus*) floating in the water column of the ocean.

Cladistics and phenetics represent two distinct methodologies for classifying organisms within taxonomic systems.

Phenetics

Phenetics, or numerical taxonomy, classifies species based on the total number of shared phenotypic characteristics. This approach relies on numerical analysis of observable characters, grouping organisms by overall similarity regardless of their evolutionary history or ancestry. Because it ignores evolutionary relationships, phenetics is no longer considered a primary method for determining phylogeny.1

Cladistics

Cladistics defines taxa based solely on inferred evolutionary relationships and most-recent common ancestors. Rather than using all available traits, it focuses on synapomorphies—shared derived characteristics that indicate descent from a single common ancestor. By organizing organisms into a branching hierarchy, cladistics ensures that all members of a specific taxon share the same evolutionary lineage.12

For example, while phenetics might group organisms based on superficial resemblance, cladistics would classify crocodiles and birds together due to their shared evolutionary history, distinguishing them from other groups like lizards.1