title: Revisiting a Classic Study of the Molecular Clock.
abstract: A constant rate of molecular evolution among homologous proteins and across lineages is known as the molecular clock. This concept has been useful for estimating divergence times. Here, we revisit a study by Richard Dickerson (J Mol Evol 1:26-45, 1971), wherein he provided striking visual evidence for a constant rate of amino acid changes among various evolutionary branch points. Dickerson's study is commonly cited as support of the molecular clock and a figure from it is often reproduced in textbooks. Since its publication, however, there have been updates made to dates of common ancestors based on the fossil record that should be considered. Additionally, collecting the accession numbers and carefully outlining Dickerson's methods serves as a resource to students of the molecular clock hypothesis.
authors.affiliation: Department of Biology, Saint Joseph's University, 5600 City Ave., Philadelphia, PA, 19131, USA.
authors.forename: Lauren M
authors.initials: LM
authors.lastname: Robinson
authors.affiliation: Department of Biology, Saint Joseph's University, 5600 City Ave., Philadelphia, PA, 19131, USA.
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Boland
authors.affiliation: Department of Biology, Saint Joseph's University, 5600 City Ave., Philadelphia, PA, 19131, USA. jbraverm@sju.edu.
authors.forename: John M
authors.identifier: http://orcid.org/0000-0002-0311-9221
authors.initials: JM
authors.lastname: Braverman
mesh_terms: D005075:Biological Evolution; D019143:Evolution, Molecular; D005580:Fossils; D014644:Genetic Variation; D008957:Models, Genetic; D010802:Phylogeny
keywords: Constant rate of evolution; Dickerson’s graph; Molecular clock; Protein evolution