Fluctuating selection: the perpetual renewal of adaptation in variable environments

Area of Science:

• Evolutionary Biology
• Quantitative Genetics

Background:

• Traditional evolutionary biology favored gradualism, proposing slow change over long periods.
• This view, supported by infinitesimal models, is challenged by recent findings of strong selection and adaptation via few genes.

Purpose of the Study:

• To reconcile discrepancies between gradualism and observed rapid adaptation.
• To propose an alternative model incorporating environmental and selection fluctuations.

Main Methods:

• Review of field surveys demonstrating strong natural selection.
• Analysis of quantitative trait loci and genomic studies on adaptation.
• Examination of long-term studies on selection dynamics in natural populations.

Main Results:

• Environmental and biotic factors vary across all time scales, increasing environmental variance.
• Natural selection intensity and direction fluctuate, increasing phenotypic variance.
• Long-term studies confirm frequent changes in selection direction.

Conclusions:

• The traditional gradualist model needs supplementation.
• Adaptation is often driven by oligogenic variation under strong, fluctuating selection.
• This provides a more realistic account of evolutionary change.