Dating by scent
Furthermore, one would presume that said difference in genes would impart a difference in fitness as well, which could potentially be chosen or selected for.
Generally, the extreme polymorphism of MHC genes is selected for by host-parasite arms races (the Red Queen hypothesis); however, disassortative mate choice may maintain genetic diversity in some species.
Chemosensation, which is one of the most primitive senses, has evolved into a specialized sensory system.Each MHC protein binds to a specific peptide sequence, yielding a set of uniquely bound peptide-MHC complexes for each individual.During cellular turnover, the MHC-peptide complex is shed from the cell surface and the fragments are dispensed in bodily fluids such as blood serum, saliva, and urine.Studies suggest that the MHC is involved in mate choice for many vertebrates through olfactory cues.There are several proposed hypotheses that address how MHC-associated mating preferences could be adaptive and how the MHC has maintained its enormous allelic diversity.
This enables the parasite to escape this cycle of frequency-dependent selection, and such a cycle eventually leads to a co-evolutionary arms race that may support the maintenance of MHC diversity.