As the title suggests, what is the direct and indirect selection of genes. Couldn't find a straightforward answer. Is it the same as direct and indirect fitness?
Direct selection is when the fitness is directly associated with a certain gene. The beneficial alleles of this gene get selected.
When an allele gets selected not because of its direct effect on fitness but because of other reasons for e.g. strong linkage with other genes which in turn are being selected, then it is said to be undergoing indirect selection.
Female preferences have caused the evolution of extreme male mating displays throughout the animal kingdom (1–3). One mechanism that might establish these preferences is indirect selection, which occurs when preference genes are associated (that is, in linkage disequilibrium) with other genes that are spreading under selection. Indirect selection is invoked by two types of theories (2). The first are “good genes” theories, which interpret male mating displays as indicators of high viability. In this view, the expression of the male display is correlated with the presence of alleles that increase viability. Because associations naturally develop between preference genes and male trait genes, as the high viability alleles spread by natural selection, preference alleles for extreme displays also spread. The second class of theories that postulates indirect selection involves a “runaway process.” Here alleles that exaggerate a male mating display decrease survival but nevertheless spread because they enhance male mating success. Genes for extreme preferences can then be established as the result of their associations with these spreading male trait genes.