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Plesiomorphy

An ancestral character state, inherited from deep in the past - the "default" part of the body that predates a lineage's own novelties. Five digits in tetrapods is a plesiomorphy: nearly everyone has it, because the common ancestor did. It is not wrong in itself, but it cannot group anyone, because a trait everybody carries says nothing about who is whose close relative. Its opposite is the derived state, the apomorphy.