Relationship of Phylogeny to a "Natural" Classification

    The network indicates the phylogeny (evolutionary history) of select primates, including apes, monkey, and pro-simians. The creatures shown are part of a single evolutionary lineage that has been assigned the taxon (plural, taxa) name Primata at the category rank of Order. The order Primata includes several families (ending in -idae) including Pongidae (Great Apes including Humans), Hylobatidae (Lesser Apes), Cercopithecidae (Old World Monkeys), and Cebidae (New World Monkey), each of which contains several genera (sing., genus). Each of these names labels a complete branch in the evolutionary tree. Several of the genera include two (or more) species (sing., species). [Without exception, genus names are always capitalized, and species names are always in lowercase].

    This system is hierarchical because the membership of any named category (species, genus, family, order, etc.) is entirely contained within a successively more inclusive category, and so on. The categories themselves combine into recognized groups: P+H = Apes, P+H+C = Old World monkeys , and P+H+C+C' = Simians (Man-like) including New World Monkeys, not including the lemur-like Tarsiers.

    The system is "natural" because the hierarchy of names indicates the degree of evolutionary relationship among organisms. For example, organisms placed in the same genus are necessarily more closely related than those in different genera in the same family, and organisms in the same family are more closely related than those in different orders.

    In this system, relationship determines classification. In previous systems, classification was determined by perceived similarity, and the Great Apes (Pongo, Gorilla, & Pan) were placed in one family (Pongidae) and humans in another (Hominidae). This taxonomy obscured their true relationships, that chimps were the closest relatives of humans, and orangutans (Pongo) were distant relatives to all the others.

    The phylogeny shown here is inferred from molecular data, in this case complete mitochondrial DNA genome sequences (ca.16,600 base pairs @). Numbers above each branch indicate the number of nucleotide substitutions inferred to occur along that branch (Maximum Parsimony); numbers in bold below indicate the statistical support for a branch (Bootstrap). The genetic differentiation between any two species can be measured by summing the branch lengths between them.