Molecular clocks Current Biology Michael S.Y. Lee, Simon Y.W. Ho  Current Biology  Volume 26, Issue 10, Pages R399-R402 (May 2016) DOI: 10.1016/j.cub.2016.03.071 Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 1 The simplest molecular clock approach for inferring evolutionary timescales. The rate of genetic change is first ascertained for one part of the tree of life (e.g. primates), often by calibrating the amount of genetic divergence to the absolute age of divergence as suggested by the fossil record. This rate is then extrapolated across the rest of the tree, allowing relative genetic divergences between all other taxa (e.g. carnivores) to be translated into absolute time, even without recourse to fossil evidence. Current Biology 2016 26, R399-R402DOI: (10.1016/j.cub.2016.03.071) Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 2 Modern molecular clocks can accommodate complex variation in rates of genetic change across the tree of life. (A) Rate variation across sites: gene 1 evolves rapidly but gene 2 evolves slowly, across all lineages. (B) Rate variation across lineages: genes 1 and 2 both evolve rapidly in clade X. (C) Rate variation across time periods or ‘epochs’: genes 1 and 2 both evolved rapidly between 140 and 80 Ma. (D) Site and lineage effects can interact, so different sites exhibit different rate patterns across lineages: here, gene 1 evolves rapidly in clade X, but gene 2 shows no such pattern (Silhouettes by A. Palci). Current Biology 2016 26, R399-R402DOI: (10.1016/j.cub.2016.03.071) Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 3 Divergence dates derived from molecular clocks are often older than those suggested by the fossil record. The molecular estimate for the date when flowering plants split from conifers (age of total-group angiosperms) and the date of the oldest divergences within flowering plants (age of crown-group angiosperms) are both much older than dates implied by the fossil record. (Water lily image by Brian Choo; Amborella image by Scott Zona.) Current Biology 2016 26, R399-R402DOI: (10.1016/j.cub.2016.03.071) Copyright © 2016 Elsevier Ltd Terms and Conditions