Evolutionary Tempo, Supertaxa, and Living Fossils

Area of Science:

• Evolutionary biology
• Molecular evolution
• Phylogenetics

Background:

• The relationship between molecular change rates and diversification has been theoretically and empirically discussed.
• Understanding evolutionary patterns requires integrating molecular evolution and diversification dynamics.

Purpose of the Study:

• To develop a novel model, the Covariant Evolutionary Tempo (CET) model, integrating diversification and molecular evolution.
• To explore how a continuously changing 'tempo' variable influences molecular, morphological, and diversification rates.

Main Methods:

• Developed the Covariant Evolutionary Tempo (CET) model.
• Treated the 'tempo' variable as continuously changing and proportional to its own value.
• Integrated molecular evolution, morphological rates, and diversification within a single framework.

Main Results:

• Predicted that diversity is dominated by a few large clades with explosive early radiations and high molecular evolution rates.
• Showed that extant organisms likely evolved from species with fast evolutionary rates.
• Demonstrated that molecular change is largely independent of lineage 'height', weakening the molecular clock hypothesis.
• Explained the existence of species-poor 'living fossil' sister groups with slow evolutionary rates.

Conclusions:

• The CET model provides a unified framework for understanding evolutionary patterns.
• Observed historical evolutionary patterns can be modeled without invoking unique mechanisms or innovations.
• The model accounts for non-uniform evolutionary rates and the prevalence of large clades.