An ancestral (or primitive) trait/character is a feature inherited from the common ancestor of the species/group of interest, while derived traits are those that were absent in the last common ancestor of the group of interest. For example, considering mammals as the target group, the presence of hair is a shared derived trait relative to other vertebrates, i.e., amphibians, reptiles, and birds. However, this trait (hair) is ancestral for humans since the genetically closest species to humans (e.g., chimpanzees) also have hair.
