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.

The truth, of course, is that the only necessary and sufficient condition for human beings to murder one another is the simple fact of being human.

All behavioral or mood disorders - including depression, OCD, ADHD and addiction - have some neurochemical components, but sufferers can still work to overcome them.

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.

Kids whose puberty begins too soon face not just psychological risks, but physical ones too, with an increased likelihood of cancer, as well as skeletal changes that could prevent them from attaining their full adult height.

There are a lot of downsides to being male. We age faster and die younger. But give us this: we're lifetime baby-making machines. Women's reproductive abilities start to wane when they're as young as 35. Men? We're good to go pretty much till we're dead.

Spending $1 for a brand new house would feel very, very good. Spending $1,000 for a ham sandwich would feel very, very bad. Spending $19,000 for a small family car would feel, well, more or less right. But as with physical pain, fiscal pain can depend on the individual, and everyone has a different threshold.