Estimating the rate of evolution of the rate of molecular evolution

A simple model for the evolution of the rate of molecular evolution ispresented. With a Bayesian approach, this model can serve as the basis forestimating dates of important evolutionary events even in the absence ofthe assumption of constant rates among evolutionary lineages. The methodcan be used in conjunction with any of the widely used models fornucleotide substitution or amino acid replacement. It is illustrated byanalyzing a data set of rbcL protein sequences.