There was an interesting article a few years ago in the New York Times magazine called Understanding the Anxious Mind by ROBIN MARANTZ HENIG. It discusses a study of anxiety that looks at subjects from birth as they age. Here is one interesting excerpt:
"LOOKING AT THE neurology of anxiety raises the inevitable question of why a trait that causes so much mental anguish would have evolved in the first place. For the species as a whole, it is most likely an advantage to have some group members who are hypervigilant and who see everything as a threat, always ready to sound an alarm and leap into action. For the individual, though, being inhibited can mean having fewer mating opportunities, not to mention the psychic burden, wearing yourself ragged with a brain that’s always on high alert.Here is the link to the letters about the original column
In the modern world, the anxious temperament does offer certain benefits: caution, introspection, the capacity to work alone. These can be adaptive qualities. Kagan has observed that the high-reactives in his sample tend to avoid the traditional hazards of adolescence. Because they are more restrained than their wilder peers, he says, high-reactive kids are less likely to experiment with drugs, to get pregnant or to drive recklessly. They grow up to be the Felix Ungers of the world, he says, clearing a safe, neat path for the Oscar Madisons.
People with a high-reactive temperament — as long as it doesn’t show itself as a clinical disorder — are generally conscientious and almost obsessively well-prepared. Worriers are likely to be the most thorough workers and the most attentive friends. Someone who worries about being late will plan to get to places early. Someone anxious about giving a public lecture will work harder to prepare for it. Test-taking anxiety can lead to better studying; fear of traveling can lead to careful mapping of transit routes.
Kagan told me that in the 40 years he worked at Harvard, he hired at least 200 research assistants, “and I always looked for high-reactives. They’re compulsive, they don’t make errors, they’re careful when they’re coding data.” He said he would bet that when the United States sends people up in space, the steely, brave astronauts were low-reactive as infants, and the mission-control people down on the ground, doing the detail work that keeps the craft aloft, were high-reactive.
An anxious temperament might serve a more exalted function too. “Our culture has this illusion that anxiety is toxic,” Kagan said. But without inner-directed people who prefer solitude, where would we get the writers and artists and scientists and computer programmers who make society hum? Kagan likes to point out that T. S. Eliot suffered from anxiety, and that biographies indicate that he was a typical high-reactive baby. “That line ‘I will show you fear in a handful of dust’ — he couldn’t have written that without feeling the tension and dysphoria he did,” Kagan said."