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Selection for altruism through random drift in variable size populations
Bahram Houchmandzadeh1, Marcel Vallade
1Univ, Grenoble 1/CNRS, Grenoble, France. bahram.houchmandzadeh@ujf-grenoble.fr
BMC Evolutionary Biology
|May 12, 2012
Summary
Altruistic behaviors can evolve even with a fitness cost. This study shows that altruism can increase random drift, favoring altruistic genes over selfish ones, especially in structured populations.
Area of Science:
- Evolutionary biology
- Population genetics
- Behavioral ecology
Background:
- Altruism, defined as costly helping, appears widespread despite selection against it.
- Existing models (kin/multilevel selection) explain altruism via group benefits, often using deterministic or frequency-dependent fitness models.
Purpose of the Study:
- To investigate a novel mechanism for the evolution of altruism.
- To explore the role of stochasticity and population dynamics in altruism.
- To present a model that does not rely on kin or multilevel selection.
Main Methods:
- Developed a generalized Fisher-Wright/Moran model.
- Incorporated variable population size dependent on altruist numbers.
- Employed numerical and analytical calculations, including large population limits.
Main Results:
- Altruistic alleles can increase random drift, enhancing their fixation probability over selfish alleles.
- Even with lower individual fitness, altruists can outcompete selfish individuals.
- Geographic structuring significantly amplifies altruistic advantages, potentially driving selfish alleles to extinction.
Conclusions:
- Altruism can evolve via random drift in populations with variable carrying capacity.
- This mechanism offers an alternative to kin and multilevel selection theories.
- The model generalizes classic population genetics frameworks by linking carrying capacity to altruistic behavior.
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