At your wedding reception, when your mother is giving you disgusted looks for not recognizing great-aunt Bessie, a lady who you haven't seen, let alone had your cheeks pinched by, in the last 25 years, you can blame it on your genes. And, if we understand biology correctly, there's a pretty darn good chance those genes were inherited straight from good ole mom or dad. As soon as we are born, humans are hard-wired to perceive and respond to faces and studies have shown that we prefer to stare at faces over inanimate objects - people even see faces in things and places where there aren't any (hey, the Man in the Moon).
However, some of us just aren't as good and recognizing and classifying faces as well as the next guy. Usually this is just because we are too busy or distracted to take in all the details to remember the person at the next encounter. But, in extreme cases, this inability to recognize faces is called "prosopagnosia" and is mostly inherited, although it can be caused by an injury to the brain. During several separate studies on twin siblings, scientists have made a link that correlates this cognitive problem to an inherited gene.
So don't fret when Mrs. O'Neil walks over to congratulate you on the nuptials and her face doesn't register at all even when she says, "I'm little Johnny's mother, you played together in the first grade." You can feign a headache by putting your hand up to your temples and tell her you've been suffering from a rare case of prosopagnosia that you caught from your parents! On the other hand, if you're worried that your friends are going to forget who YOU are, consider presenting them with memorable groomsmen gifts -- a snapshot of your smiling mug displayed in a keepsake photo frame makes great gifts for the guys.