What is Second-Order Selection?

[jacobaf20]

Can someone please explain to me what is second-order selection? Barring that, a link to a simple explanation somewhere online would be extremely helpful. I'm having a terribly difficult time trying to find a clear explanation.

[Luxorien]

As far as I can tell, second-order selection is the action of natural selection on an allele that only indirectly affects an organisms ability to survive and reproduce. Second-order selection occurs when certain locations on the genome are affecting the expression of genes rather than coding for proteins themselves.

Alternatively, we can ask how evolution within a population affects the mutation rate. This can be done by postulating a locus that affects the mutation rate of other genes. This locus might, for example, encode a DNA repair enzyme. For simplicity, let us assume that alleles at this locus do not differ in their direct effect on the fitness of their bearers - they do not directly affect survival or reproduction. They have only an indirect effect via mutations they allow or prevent. Such a locus is often called a MODIFIER of mutation, and the action of natural selection on such a locus is termed SECOND-ORDER SELECTION. Models of second-order selection on modifier loci are the most useful devices for understanding the evolution of genetic systems.

Source: Futuyma, D.J. (1998). Evolutionary Biology, 3rd ed. Sinauer: Sunderland, MA. Pgs 605-606.