 The dynamics of the warm/cold system cannot be inferred from a type recursion in which fitness coefficients are set equal and next-generation frequencies are determined entirely by the “drift” term, effective population size in the binomial sampling equation. When fitnesses are equal, the frequency of each type is determined solely by the binomial sampling equation above (since post-selection frequency, the input to the sampling equation, is just pre-selection frequency). Such a determination makes next-generation frequency a normal, bell-shaped distribution whose mean is the initial frequency of the types in the system. The distribution of next-generation frequencies in the warm/cold system does not look like this. The type recursions for the warm/cold system must be calculated using a temporally variable selection model: