Unveiling the tempo of molecular and morphological evolution across the Tree of Life

The evolution of Earth’s vast genetic and morphological diversity has been explained by an array of macroevolutionary models. At opposite ends of the spectrum lie two contrasting evolutionary models: phyletic gradualism and punctuated equilibria. Under a phyletic gradualism framework, evolutionary change accumulates along lineages and species are steadily transformed into new forms over time. In contrast, under punctuated equilibria, evolutionary change tends to occur in bursts at speciation events. Previous studies of molecular and morphological data have found varying levels of support for the two evolutionary models. We examined these models using comprehensive molecular and morphological data sets from 40 clades across the Tree of Life. Testing for associations between species richness and the amount of evolutionary change in sister clades, we find little evidence to support the punctuated equilibria model. However, we found high levels of among-lineage rate variation in molecular evolution and particularly morphological evolution. Our comparison of coding and non-coding genomic regions revealed contrasting patterns of among-lineage rate variation, without clear trends across taxa. Our study confirms that heterotachy is a dominant feature in macroevolution and that molecular and morphological evolution cannot simply be described by either a gradual or punctuated model.