Positively versus Negatively Frequency-Dependent Selection

Frequency-dependent selection (FDS) refers to situations where individual fitnesses are dependent (to some degree) on where the individual’s alleles lie in the proximate allele frequency distribution. If the dependence is negative – that is, if alleles become increasingly detrimental to fitness as they become increasingly common at a given locus – then genetic diversity may be maintained. If the dependence is positive, then alleles may converge at given loci. A hypothetical evolutionary model of FDS is here presented, in which the individuals themselves determined – by means of a gene – whether their fitnesses were positively or negatively frequency-dependent. The population ratio of the two types of individual was monitored in runs with different parameters, and explanations of what happened are offered.