Word: mhc
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Scent not only tells males which females are primed to conceive, but it also lets both sexes narrow their choices of potential partners. Among the constellation of genes that control the immune system are those known as the major histocompatibility complex (MHC), which influence tissue rejection. Conceive a child with a person whose MHC is too similar to your own, and the risk increases that the womb will expel the fetus. Find a partner with sufficiently different MHC, and you're likelier to carry a baby to term...
Studies show that laboratory mice can smell too-similar MHC in the urine of other mice and will avoid mating with those individuals. In later work conducted at the University of Bern in Switzerland, human females were asked to smell T shirts worn by anonymous males and then pick which ones appealed to them. Time and again, they chose the ones worn by men with a safely different MHC. And if the smell of MHC isn't a deal maker or breaker, the taste is. Saliva also contains the compound, a fact that Haselton believes may partly explain the custom...
Precise as the MHC-detection system is, it can be confounded. One thing that throws us off the scent is the birth-control pill. Women who are on the Pill--which chemically simulates pregnancy--tend to choose wrong in the T-shirt test. When they discontinue the daily hormone dose, the protective smell mechanism kicks back in. "A colleague of mine wonders if the Pill may contribute to divorce," says Wysocki. "Women pick a husband when they're on birth control, then quit to have a baby and realize they've made a mistake...
...only does kissing serve the utilitarian purpose of providing a sample of MHC, but it also magnifies the other attraction signals-if only as a result of proximity. Scent is amplified up close, as are sounds and breaths and other cues. And none of that begins to touch the tactile experience that was entirely lacking until intimate contact was made. "At the moment of a kiss, there's a rich and complicated exchange of postural, physical and chemical information," says Gallup. "There are hardwired mechanisms that process all this...
...deliver the goods. For all the joy it promises, it can also play us for fools, particularly when it convinces us that we've found the right person, only to upend our expectations later. Birth-control pills that mask a woman's ability to detect her mate's incompatible MHC are one way bad love can slip past our perimeters. Adrenaline is another. Any overwhelming emotional experience that ratchets up your sensory system can distort your perceptions, persuading you to take a chance on someone you should avoid...