"That's the general agreement on why this temperament survives in the gene pool," he says. "If you look back through history, some of our most esteemed public figures, the people who really made important political or scientific or philosophical or literary contributions, you'll find introverted people terribly over-represented relative to their prevalence in the population as a whole."
They may get sick a lot easier, but many of them are driven to do things "that are exceptional or remarkable," he says.
It took a deadly virus to point the way toward understanding the relationship between personality and health. During the early years of AIDS, researchers kept close tabs on patients who were suffering from that horrible disease, and they soon saw a correlation.
Among those infected with the virus, the "socially inhibited, shy, sensitive, introverted people got sick and died something like two to three years earlier" than others with the virus, Cole says.
"So we knew there was something going on there, a real relationship," he adds.
The participants in the recent study were given a series of psychological tests to determine which ones were truly introverted. Then all 54 men were subjected to various types of stress, like answering simple math questions and being chastised if they got the answer wrong.
Response to that stress was measured by monitoring such things as blood pressure, perspiration, and pulse, all conditions that are influenced by the autonomic nervous system which controls involuntary bodily functions.
The researchers also measured the rate at which the virus was replicated in each patient and other indicators of how the patient was responding to treatment.
"The study surprised us by showing that it's precisely the people who have these high nervous system responses, the shy, sensitive, introverted people, who fail to show complete benefit following drug treatment," Cole says. "There is something about their body that is supporting the virus more than in other patients."
The Next Step to Understanding
That shows there is an "exceptionally strong correlation" between personality and infectious diseases, he says, but one more step is needed.
The researchers have just embarked on a new project, and they hope that it will show whether the stress that is so inflamed in shy people is the villain. They aren't going to try to change anybody's personality, but they are going to try to inhibit the consequences of stress, and they can do that with off-the-shelf drugs used for heart disease, common beta blockers.
These drugs suppress the effects of stress by keeping such things as blood pressure in check. If patients who are diagnosed as introverted respond just as well as extroverts while their autonomic nervous system is suppressed then it clearly is stress, induced by their heightened sensitivity, that is the link between personality and infectious diseases, Cole says.
It will be a year or two before he knows if he is right. If he is, it should be possible to produce drugs that reduce the physiological impact of stress among ailing shy folks, thus helping them fight off an infectious disease.