  Population dynamics models the evolution of populations. A population is a collection of individuals, which are categorized according to type. The types in genetics are genes, in evolutionary game theory, strategies. The types of interest in epistemological models would be types of cognitive apparatuses, or cognitive strategies — ways of responding to environmental cues, ways of manipulating representations, and so forth. Roughly, EEM models focus on the inherited and EET models focus on the learned. The evolution of the population consists in changes of the relative frequency of the different types within the population. Selection, typified by differential reproductive success, is represented as follows. Each type has a growth rate or “fitness”, designated by \(w\), and a frequency designated by \(p\). The frequency of type \(i\) at the next generation \(p'_i\) is simply the old frequency multiplied by the fitness and divided by the mean fitness of the population “\(\overline{w}\)”.