Does a correlation between cladogenesis and anagenesis exist?
According to classical evolutionary theories, there should be no correlation between cladogenesis and anagenesis (between speciation and changes in the phenotype of organisms), while the frozen plasticity theory assumes that the irreversible phenotypic changes are always associated with speciation. The frozen plasticity theory predicts that the number of evolutionary changes in a phylogenetic lineage reflects the number of speciations in this line rather than its age. These two parameters often correlate with each other; however, modern multivariate statistical techniques allow testing the effects of these two parameters separately. A study in passerine birds has found the number of speciations within a phylogenetic line to have a very strong positive effect on the rate of anagenesis. The number of species alone explained 33.3% of the total variation in morphology. A positive correlation between the rates of anagenesis and speciation can be detected even on the molecular level. A molecular study has shown that a relatively large part of the variability in the substitution rate can be explained by differences in the speciation rate between evolutionary lineages.