When choosing a partner to have children with, it is only natural to desire “Prince Charming” or “Cinderella,” who may pass on their beneficial genetic qualities to future kids. Given that better genes increase the offspring's survival and reproduction chances, mechanisms that detect “genetic quality” should have evolved to lead people to be sexually attracted to “knights in shining genes.”
One such cue for mate suitability is odor, which signals compatibility between potential mates' immune systems. Specifically, odor indicates the extent of overlapping between potential mates' immune systems, such that more attractive odor signals less overlap between mates' immune systems. The larger the dissimilarity between mates' immune systems, the more threats the immune system can combat.