Dating species divergences using rocks and clocks

Knowledge of absolute species divergence times is not only fascinating to evolutionary biologists in establishing the age of a species group, but also critically important to addressing a variety of biological questions. Absolute times allow us to place speciation events (such as the diversification of the mammals relative to the demise of the dinosaurs) in the correct geological and environmental contexts and to gain a better understanding of speciation and dispersal mechanisms [1,2]. They also allow us to characterize species richness and species diversification rates over geological periods. Estimated molecular evolutionary rates can also be correlated with life-history traits and are important for interpretation of the fast-accumulating genomic sequence data. Molecular clock methods are also used widely in establishing the evolutionary history of viruses, including those related to human diseases.