  In their well-known textbook (Vincent & Brown, 2005), Vincent and Brown
suggested an attractive approach for studying evolutionary dynamics of
populations that are heterogeneous with respect to some strategy that affects
the fitness of individuals in the population. The authors developed a theory,
whose goal was to expand the applicability of mathematical models of population
dynamics by including dynamics of an evolving heritable phenotype trait subject
to natural selection. The authors studied both the case of evolution of
individual traits and of mean traits in the population (or species) and the
dynamics of total population size. The authors consider the developed approach
as (more or less) universally applicable to models with any fitness function
and any initial distribution of strategies, which is symmetric and has small
variance. Here it was shown that the scope of the approach proposed by Vincent
& Brown is unfortunately much more limited. I show that the approach gives
exact results only if the population dynamics linearly depends on the trait;
examples where the approach is incorrect are given.
