'Basal' is a term inbiology for 'primitive' or 'ancestral'. Basal is preferred because it is neutral and non-judgmental. This terminology came into use withcladistics. The term is used inevolution andclassification to mean the group which gave rise to later forms. It is a term which works at any level: a basalspecies gives rise toderived species, and a basal group gives rise to derived groups.

'Derived' is the correct term inbiology forspecialised oradvanced. It is used for groups which have evolved from a more basal group. Aderived trait is atrait that is present in anorganism, but was not in the lastcommon ancestor of the group being considered. Simplicity is often secondarily derived.^[1] For example, nomitochondria in the anaerobicprotistEntamoeba histolytica is a result of their secondary loss.

General view –

• Basal group
  • Derived group
  • Derived group
  • Derived group

Example –

• Earlyprimates
  • Monkeys
    • Apes
      • Homo

In the last example, note that apes arederived from monkeys butbasal with respect to our owngenus. The status of being basal or derived is relative, though living species can only be derived. In any basal-derived pair, the basal member must have evolved before the derived member, with evidence that some of its species gave rise to (evolved into) the derived member.^[2]

See also Wileyet al. 1991.^[3]

• Ancestraltaxon = basal group
• Characters or attributes:
  • Plesiomorphy = ancestraltrait inherited from earlier forms.
  • Apomorphy = trait or innovation derived from a plesiomorphic character. It may define a clade.
  • Synapomorphy = a trait or character of a whole clade.