Spit and Smell Your Way to Marital Bliss

Image courtesy of Frans De Waal

It’s no secret that many mammals choose their mates based on smell. The body has a collection of genes called the major histocompatibility complex (MHC) that help the immune system identify foreign cells, like viruses or bacteria, and determine the appropriate course of action against them. Hundreds of variations of these genes exist in humans, and the more different types a person has, the more pathogens their bodies are capable of fighting off. If mates have extremely different MHC variations, their offspring will be better equipped to fend off disease, and some scientists speculate that mammals can determine such genetic dissimilarity through smell. Specific MHC combinations are transmitted through bodily fluids and are present on the surface of the skin, and a small pit inside of the nose called the vomeronasal organ detects pheromones and other molecules, including ones from the MHC.