Introverts have it rough: They sweat bullets when speaking in a crowd; they play the wallflower at dances. And, says psychologist Sonia Cavigelli of the University of Chicago, they may live shorter lives than their gregarious peers. Her experiments in rats are the first to link a personality trait detectable in infancy to an increased risk of premature death.
To clarify the relationship between “neophobia”—a fear of novelty associated with shyness in both animals and humans—and life span, Cavigelli and her team classified baby male rats based on their reaction to unfamiliar objects. While normal animals interacted readily with the new items, rats identified as neophobic hung back in fear and touched the objects less frequently. Subsequent monitoring showed that the neophobic animals developed higher levels of stress hormones known as glucocorticoids in response to experimental challenges. Cavigelli suspects that the surging hormone levels take a toll on the animals’ defenses against illness. “We know there’s an interaction between stress hormones and the immune system,” she says.
Among humans, however, shy individuals may not be at that much of a disadvantage, Cavigelli says. Her rats were tested in a controlled laboratory setting, where lack of fear had no real drawback. In the human world, people who are attracted to novelty might have daredevil tendencies that make them more likely than cautious individuals to die as a result of an accident. “You might see harmful effects in shy humans at the end of life in particular,” she says. “But in the prime of life, you might actually get an opposite effect.”