When you learn conflict-resolution skills in the playroom, you then practice them on the playground, and that in turn stays with you. If you have a combative sibling or a physically intimidating, older sibling, you learn a lot about how to deal with situations like that later in life. If you're an older sibling and you have a younger sibling who needs mentoring or is afraid of the dark, you develop nurturing and empathic skills that you wouldn't otherwise have.

When you're your parents' one shot at a genetic legacy, you may get to attend all the best schools, wear all the best clothes and eat all the best foods - at least relative to children in multiple-sibling households. But you also wind up with an overweening sense of your own importance.

People with anxiety disorders such as OCD know that nothing can be more paralyzing than having too many options. Go to a store to buy a sweater, find four that you like and the odds are pretty good you'll stare and stare... and buy nothing at all.

The mind of the polyglot is a very particular thing, and scientists are only beginning to look closely at how acquiring a second language influences learning, behavior and the very structure of the brain itself.

It's a deep and all but certain truth about narcissistic personalities that to meet them is to love them, but to know them well is to find them unbearable. Confidence quickly curdles into arrogance; smarts turn to smugness, charm turns to smarm.

Learning to speak was the most remarkable thing you ever did.

Tamerlan Tsarnaev is telling no tales. The older of the two brothers who committed the Boston Marathon bombings was likely the one who planned the attack, but when he died in a shootout with police just days after the blasts, his thoughts and motivations vanished with him.