The tenuousness of modern life can make anyone feel overwrought. And in societal moments like the one we are in — thousands losing jobs and homes, our futures threatened by everything from diminishing retirement funds to global warming — it often feels as if ours is the Age of Anxiety. But some people, no matter how robust their stock portfolios or how healthy their children, are always mentally preparing for doom. They are just born worriers, their brains forever anticipating the dropping of some dreaded other shoe. For the past 20 years, Kagan and his colleagues have been following hundreds of such people, beginning in infancy, to see what happens to those who start out primed to fret.