Can a firstborn son and a firstborn daughter live happily ever after? Not according to this new book. They'd be likely to experience what's known as "rank conflict," or the urge to tear each other limb by limb in a battle for control, which they're both used to having. Decrypting what order you're born in, and who it means you're meant to love, is this tome's goal. So I put it to a quick test: While I half-buy the concept of birth order, I'm an older sister of sisters, and according to this my best match is the younger brother of sisters, a younger brother of brothers, an older brother of sisters or—okay, I might be into this, just because it sounds slightly lascivious—a male twin. Hmm, too bad I'm head over heels for a male only child. But, amazingly, I'm one of his "perfect" matches. Not sure how that works, but I did discover that reading your chapter is riveting, even if you don't agree. Here's where you can learn more about the book. Or, just enjoy a few birth order tidbits, handy for dropping at your next cocktail party: - Sex conflict occurs when people with no opposite-sex siblings enter into relationships. They can be expected to experience difficulty understanding each other since they didn't grow up with opposite-sex peers. -Narcissistic attraction entails falling in love with someone who resembles yourself. These are also known as relationships of identification. (And here's how to find out if he's a narcissist, all on his own.) -Interactive relationships occur between people who are different, such as a firstborn and a lastborn. This is seen as a positive thing, a step above a narcissistic pairing, which is essentially...falling in love with yourself. -Duplication theorem is a theory by Walter Toman that people will be happiest in relationships with those who duplicate their early sibling relationships, i.e., an older brother of a sister does best with a younger sister of a brother. The only thing the book didn't cover was Flowers In the Attic Syndrome, of which Angelina and her bro seem to be a great case study.