The structure of this commentary is as follows. First I discuss differential
equations and show that they are more common in demography than is generally
accepted, and that they can be used to develop theories of population dynamics. The
integration of mathematical modeling with differential equations, and statistical modeling
with regression equations, is illustrated. In the following section I briefly discuss software.
That discussion leads to a concrete proposal: to use a software package or computer
language that facilitates both statistical and mathematical modeling. That language is R, a
free software environment for statistical computing and graphics that has utilities to solve
differential equations. Section 4 is the conclusion.