The fundamental theorem of natural selection in Ewens' sense (case of many loci).

We correct an equation characterizing the additive allelic effects on fitness determined at many loci without the assumption of random mating given in Ewens (1989, 1992) and we show that the additive genetic variance in fitness divided by the mean fitness is equal to a partial change in the mean fitness from one generation to the next as stated in Ewens (1989).