A synthetic theory of molecular evolution

Area of Science:

• Population genetics
• Evolutionary biology
• Theoretical biology

Background:

• The neo-Darwinian view posits evolution rate (nu) depends on environmental variation (gamma).
• The non-Darwinian view emphasizes mutation rate (mu) as the primary driver of evolution rate.
• Understanding the interplay between mutation, selection, and environment is crucial for evolutionary theory.

Purpose of the Study:

• To investigate evolutionary dynamics under different parametric conditions.
• To compare neo-Darwinian and non-Darwinian models of evolution.
• To analyze the transition between different evolutionary regimes.

Main Methods:

• Developed and analyzed two population genetics models: an infinite population dynamical model and a finite population Markov process model.
• Derived general time-derivative and mu-derivative formulas for population average quantitative traits.
• Examined the behavior of evolution rate (nu) in relation to mutation rate (mu) and environmental variation (gamma) under varying selection intensities.

Main Results:

• In infinite populations, if mutation rate is adaptively determined, mu must exceed nu in the stationary state.
• High evolution rates are consistent with tolerable genetic load under weak selection and low functional constraint.
• Discontinuous transition of nu from mu to gamma occurs with increasing selection intensity in infinite populations; a steep, non-discontinuous transition is observed in finite populations.

Conclusions:

• The steepness of the transition suggests that real molecular evolution is predominantly either neo-Darwinian or non-Darwinian.
• Intermediate forms of evolution appear to be rare.
• The findings provide insights into the fundamental mechanisms driving evolutionary change.