Despite old-fashioned wisdom about looking before you leap and fools rushing in, new research published in the Proceedings of the National Academy of Science shows that caution can actually kill you. Sonia Cavigelli and Martha McClintock of the Department of Psychology and Institute for Mind and Biology at the University of Chicago found in a recent experiment that individuals who fear novelty—a condition scientists have named "neophobia"—are likelier to die at an earlier age than those who are unafraid of change. It is the first time, says Cavigelli, a study has demonstrated that an emotional trait apparent in infancy can shorten life span.
For this research, Cavigelli and McClintock followed the lives and fortunes of pairs of rat brothers for several years. The scientists chose their subjects by first establishing which of the rats were neophobic. To do this, they placed the young rats inside a bowl in a small room. Objects the rats hadn't seen before—a rock, a metal box, a plastic tunnel—were placed in each corner of the room. The rats the scientists deemed neophobic either stayed hunkered down in the bowl or left it only hesitantly, with hunched backs, stilted walks, and bristling fur. The rats who left the bowl quickly to explore the room and the various unfamiliar objects were dubbed neophilic.
After their experience in the testing room, the neophobic rats were shown to have elevated levels of corticoid—a hormone typically secreted as part of the flight-or-fight response. Cavigelli and McClintock tested the rats repeatedly over the course of their lives and found that neophobic rats continued to have elevated corticoid levels not only in response to their frightening experience, but at other random moments throughout their lives.
A little hormonal surge can sometimes be a good thing. The flush of hormones—such as adrenaline and cortisol (the human equivalent of the rats' corticoid)—that accompany fear spur the heart to beat faster, cause breathing to increase, and generally put an organism on high alert so that it can react swiftly to get out of danger. But these stress hormones also strain the body. Too much of them can lead to a compromised immune system, the loss of brain cells, and hardening of the arteries; they can also negatively affect other important body functions such as sleep.
In fact, this kind of excess stress is so unhealthy that rats with neophobia were found to be 60 percent more likely to die at any point during their lives than their more adventurous counterparts. The scared rats were as healthy as their curious siblings during their reproductive years, but, because of the cumulative effects of the extra stress they experienced, they died sooner overall, and before they died, they aged more quickly. (All of the rats—neophobes and neophiles—died of tumors in the end; this particular strain of lab rat is prone to them. But the neophobic rats succumbed to their tumors much more quickly.)
All the neophobe/neophile rat pairs in the experiment were brothers. Because siblings are very similar genetically, Cavigelli and McClintock suggest that neophobic and neophilic tendencies are not genetically determined. The emotional traits may instead come from early experiences, such as the social roles rats play in their litter, and the different ways that their mothers groomed them.
But the point of experimental psychology is not to help shy rats get along in the world or to increase rat longevity, it's to measure phenomena that may be applicable to humans. Is it possible that neophobia in humans can affect life span in the same way?
Cavigelli thinks so. A number of parallels exist between humans and their rat surrogates. Neophobia shows up in human infants as early as 14 months of age, and like the rats, fearful children have a faster and stronger hormonal response than children who are not afraid of new situations. It's also been shown that if you are neophobic at a young age, you tend to remain that way throughout childhood. Cavigelli suggests, however, that individuals may develop strategies to avoid the negative effects of neophobia. "If you are a neophobic-type person, you might avoid any novel situations thereby minimizing that stress," she says. Staying away from stressful situations could be a form of "self-medication."
Yet the true cost of being a neophobe is the way it affects a person's vulnerability to disease rather than the length of his or her life. The wear and tear of stress hormones can cause neophobes to get sick more quickly, suggests Cavigelli. So if you know you're a neophobe—and therefore more vulnerable to any bug going around—you might want to be seek medical intervention promptly in the case of illness.
Although it looks like the neophiles have an unfair advantage, they may not have it as good as it seems. In the experiment, Cavigelli and McClintock played God by controlling the environment of their subjects and essentially creating a safe universe where being brave didn't get you into trouble. But real life, with its car accidents, plane crashes, and human predators does not always reward the fearless. Human neophiles might also have longer lives if we were all just rats in a cage.
Why a seemingly negative trait like neophobia should exist at all seems, at first, to be mysterious. Surely traits that shorten life span are of no value to a species. In fact, the incongruity is an illusion. It stems from the fact that the goals of individual humans have diverged from the goal of evolution: We all personally want to live as long as possible, but survival of the species depends only on whether we live long enough to reproduce.
As far as the rats are concerned, then, Cavigelli and McClintock think it makes evolutionary sense for mothers to have "emotionally diverse litters," consisting of scared and brave rats. In a completely safe world, neophiles will live faster and die later. But in a world in which fear is sometimes smart, then at least some neophobes will survive to perpetuate the species.