ABSTRACT
The amino acid sequences of a set of related polypeptides retain a record of the history of their evolution by natural selection. Evolution by natural selection is usually viewed from its optimistic side. The evolutionary distance between the amino acid sequences of two proteins is the value of any quantity that is thought to be directly proportional to the time that has elapsed since those proteins shared a common ancestor. If the nucleic acid sequence encoding either protein is unknown, mutations to an alternative codon for the same amino acid are also missed. The minimal mutational distances must be corrected statistically for all of these missing mutations to obtain estimates of evolutionary distances. The tabulated values of evolutionary distances are used to construct a tree the branches of which connect the species being compared. The phylogenetic tree, however, in addition to the historical sequence of events, conveys estimates of the evolutionary distances from existing species to common ancestors.
