Fluctuation driven fixation of cooperative behavior

Area of Science:

• Evolutionary biology
• Population genetics
• Behavioral ecology

Background:

• Cooperative behaviors benefit communities but appear counterintuitive to natural selection due to lower individual fitness for cooperators.
• Existing models often attribute deterministic advantages to cooperation (e.g., inclusive fitness, multilevel selection).

Purpose of the Study:

• To investigate the emergence of cooperative behaviors through stochastic evolutionary dynamics.
• To demonstrate that cooperation can arise from population size changes rather than solely deterministic selection pressures.

Main Methods:

• Utilized Wright-Fisher models in population genetics to analyze evolutionary dynamics.
• Computed the exact increase in genetic drift caused by cooperative behaviors.
• Assessed the impact of increased genetic drift on the fixation probabilities of cooperators and non-cooperators.

Main Results:

• Cooperative behaviors can increase overall population size.
• Increased population size amplifies genetic drift, acting against non-cooperators.
• A simple criterion for cooperation dominance was derived: relative population increase must exceed selection pressure against cooperators.

Conclusions:

• Cooperative behaviors can emerge and dominate due to stochastic effects, specifically amplified genetic drift.
• This emergence is driven by population size increases, offering a purely stochastic explanation for cooperation.
• The findings challenge traditional deterministic models by highlighting the role of random genetic drift in the evolution of cooperation.