“The problem with romance is that it doesn’t always 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.”