Simpson (1953 p. 140) may have been the first to conjecture that the rate of evolution of a population is a monotonic increasing function of its distance from an adaptive optimum. As Stenseth and Maynard Smith (1984) point cut, this conjecture can be construed to be a more general version of Fisher's Fundamental Theorem of Natural Selection. It is useful to try to establish such an intuitively appealing notion on a quantitative basis, as this makes explicit the assumptions behind the idea and puts it in a form suitable for further theoretical analysis. Stenseth and Maynard Smith (1984) have recently made such an attempt at quantification. They defined the rate of evolution as the rate of change of a population's mean fitness. Lag load, L, was then defined as