in non-vascular ("lower") and vascular ("higher") plants). The terms "plesiomorphy" and "apomorphy" are typically used in the technical literature: for example, when a plesiomorphic trait is shared by more than one member of a clade, the trait is called a symplesiomorphy, that is, a shared primitive trait; a shared derived trait is a synapomorphy. The amount of variation of characters can assist in depicting greater relatedness amongst species, and conversely show the lack of relatedness between species. Analysis of character variation also aids in distinguishing primitive characters from derived characters. The term derived and primitive, or ancestral, is used in reference to characters and character state. In doing so, a derived character is depicted as a character procured through evolution from the previous ancestral state, and persisting due to fixation of derived alleles. Whereas, a primitive character is one that is originally present in the ancestral population. Primitive characters are avoided as they depict the ancestral character state. Conversely, derived characters depict the alteration of characters from the ancestral state because selection favored organisms with that derived trait. Primitiveness of characters is determined by context "Primitive" and "advanced" are relative terms. When a trait is called primitive, the determination is based on the perspective from which the trait is viewed. Any trait can be both primitive (ancestral) and advanced (derived) depending on the context. Examples In the clade of vertebrates, legs are an advanced trait since it is a feature that appears in the clade. However, in the clade of tetrapods, legs are primitive since they were inherited from a common ancestor. The terms "primitive" and "advanced", etc., are not properly used in referring to a species or an organism as any species or organism is a mosaic of primitive and derived traits. Using "primitive" and "advanced" may lead to "ladder thinking" (compare the Latin term scala naturae 'ladder of nature'), which is the thought that all species are evolving because they are striving toward supremacy. When this form of thinking is used, humans are typically considered perfect and all other organisms are of less quality than them. This can cause the misconception of one species being an ancestor to another species, when in fact both species are extant. Homo sapiens, for example have large brains (a derived trait) and five fingers (a primitive trait) in their lineage. Species are constantly evolving, so a frog is not biologically more primitive