Have you ever looked at your siblings and wondered what makes them tick? Why, for instance, is your oldest brother or sister so driven, so exacting, so uncompromising? How about the baby in your family? Why can't he/she settle down? Why does he/she treat life like one big party, refusing to take anything seriously? And what about you? What makes you so demanding or so laidback or so serious-minded? Does it have anything to do with your siblings and the order in which you all came into the same family? Dr. Kevin Leman, a psychologist who's written more than 30 books on marriage, parenting and other family relationships, believes it does.

In The Birth Order Book (I read the Revised and Updated version, published in 2009), Dr. Leman discusses the idea of birth order influencing people's actions and personalities. While he admits the concept can't explain everything about a person or a family (both of which are affected by a virtually limitless list of variables throughout its lifetime), he presents pretty strong evidence to support his claims. We all know the birth order stereotypes: oldest children and only children are aggressive, goal-oriented people; middle children are easygoing, natural peacemakers; youngest kids are fun-loving comedians. Dr. Leman explains why this is so often the case. Of course, families don't always work out so predictably, but the psychologist has reasons for this, too, and, while some of his theories seem a little too convenient, a lot of them make a lot of sense.

In addition to talking about the usual stereotypes, Dr. Leman also talks about how birth order is affected by things like divorce, death, adoption, and so on. Using vivid examples, he shows how families evolve because of these kinds of life changes. His evaluations aren't always spot-on (I could think of exceptions to just about all of his rules), but more often than not, they are. It's fascinating. Not to mention a little eerie.

Besides using it to psychoanalyze yourself and others, of what use is the information in The Birth Order Book? Well, according to Dr. Leman, knowing about birth order can help you better understand your spouse (leading to a stronger marriage), your children (helping you become a better parent) and even the clients you may encounter at work (creating a more successful business as well as a larger personal income). He gives specific ideas for doing each of these things, using examples from both his professional and personal lives.