University of Michigan study challenges neutral theory of molecular evolution

Researchers at the University of Michigan have published a study challenging the neutral theory of molecular evolution — one of the most influential frameworks in modern genetics, which holds that the vast majority of mutations that become permanently established in a species are selectively neutral rather than advantageous.

The team's analysis found that beneficial mutations arise substantially more often than the neutral theory assumes. Yet these mutations rarely sweep to fixation across entire populations. The researchers argue that fluctuating selective pressures — environments that shift before a beneficial variant can spread — may explain this paradox. In effect, the fitness landscape keeps moving, leaving beneficial mutations stranded at intermediate frequencies.

The findings have implications for population genetics models used to estimate selection coefficients, interpret patterns of molecular diversity, and understand the tempo of adaptive evolution. If environmental change routinely disrupts selective sweeps, methods that assume fixation-based signatures of positive selection may systematically underestimate the prevalence of adaptive evolution.

The study was reported by ScienceDaily; the primary journal source was not specified in available feed text. Researchers and students working with population-genetic theory or molecular evolution models will find the conceptual challenge to the neutral theory of particular interest.