Evolutionary pressure

The evolutionary pressure of a trait is the magnitude of change to its mean genotype per generation. For example, if IQ changes by 10 points in a generation, and people in generation 2 would be +5 IQ in generation 1's mean environment, on average, then the evolutionary pressure on IQ was 5 points.

Evolutionary pressure has three components: selection pressure, mutational pressure, and genetic drift. Selection pressure proportional to the extent to which those who pass on their genes differ from the general population. Mutational pressure is proportional to the average effect de novo mutations have on a trait. Genetic drift is the standard error of drawing genes from the breeding population; it has a mean of 0 and its variance is proportional to the polygenicity of the trait divided by the size of the breeding population.