A plant or animal population with age-dependent survivorship and fecundity schedules, lx and mx, respectively, will settle into a stable age distribution, and that the population as a whole will grow at a rate r given by .**GRAPHIC**. Given the life tables, lx and mx, there is no difficulty in computing r to any required degree of accuracy. It is customary to use the approximation r .simeq. rc .tbd. (ln Ro)/Tc. The 2nd equation gives a clear relation between the intrinsic rate of increase, r, and the biological parameters Ro and Tc: as such, the equation provides the basis for discussions of the evolutionary significance of life history strategies, both in the classroom and in the technical literature. A simple and general expression is given for the relation between these 2 equations, i.e., between the exact r and the approximation rc: rc = r[1 - r.sigma.2/2Tc + .cntdot..cntdot..cntdot.]. Here .sigma.2 is the variance of the lxmx distribution, .sigma.2 = [.SIGMA. x2lxmx/Ro] - Tc2, and the further correction terms involve higher order moments (skewness, etc.) of the distribution.