Published online by Cambridge University Press: 28 February 2022
Variation is the fuel of evolution, but as is well known, not all variation will drive Darwin’s engine along. Within population genetics, “additivity” is one concept used to characterize the salient type of variation. The characterization of variation (variance) in terms of additivity originates with R.A. Fisher (1918), and Fisher’s “fundamental theorem of natural selection” (1930) states that the rate of evolutionary change is proportional to the additive variance in fitness in the population at that time. Evolution proceeds until the additive variance is exhausted.
It would not be surprising if a concept so important in the mathematical structure of evolutionary theory had philosophical significance. In two important works, William Wimsatt (1981) and Elisabeth Lloyd (1988) have claimed that additivity can be used to give a criterion for deciding the “unit of selection” in an evolutionary process.
I am very grateful to Sarah Otto for advice and comments. Thanks also to Richard Lewontin and Elisabeth Lloyd for helpful discussions.