Frequency-Dependent Selection, explained.
Frequency-dependent selection makes a type’s relative reproductive success depend on how common it is in the population.
Why it happens
Haploid frequencies update proportionally to fitness. Rare-type advantage uses wA=2−p and wB=1+p; the alternative reverses these advantages, changing the stability of one-half frequency.
Frequency-dependent selection makes a type’s relative reproductive success depend on how common it is in the population.
Read the result
Fitness changes with the current frequency rather than remaining fixed across generations. The chosen rule determines whether rarity is advantageous.
A worked example
Reverse the stability of an interior balance
Begin with A at twenty percent and choose rare-type advantage.
Advance generations and inspect movement toward one-half under the stated fitness functions.
Restart with common-type advantage and compare movement away from the one-half balance.
OPTIONAL DEEPER DETAILGo deeper: inside the model
Inside this model
Haploid frequencies update proportionally to fitness. Rare-type advantage uses wA=2−p and wB=1+p; the alternative reverses these advantages, changing the stability of one-half frequency.
Where this idea is useful
A practical use
Check whether a once-successful strategy loses its advantage when it becomes common.
A common misconception
“A rare type always has a selective advantage.”
Negative frequency dependence can favour rarity; positive frequency dependence can instead favour the already common type.
What this explanation leaves out
- The fitness functions are teaching assumptions, not measured coefficients. Mutation, genetic drift, diploidy and environmental change are absent.
Is the one-half equilibrium a measured natural frequency?
No. It follows from the symmetric teaching fitness functions, with no empirical organism or strategy calibration.
Would becoming common change the advantage of the type you are observing?
Associated thinkers
Associations marked provisional are awaiting source review.
Further reading
Explore the original research or the teaching reference behind this experiment.