Biology sets the context, and that is critical, but obesity still boils down to whether a person eats too much or exercises enough.

I regret not working harder to create true friendships with other couples, not seeking out people with whom to go do things and go places - people with whom to have a few crazy, memorable bonding adventures.

When a trait is universal, evolutionary biologists look for a genetic explanation and wonder how that gene or genes might enhance survival or reproductive success.

Scientists who study play, in animals and humans alike, are developing a consensus view that play is something more than a way for restless kids to work off steam; more than a way for chubby kids to burn off calories; more than a frivolous luxury.