Henry Allingham’s explanation for his amazing longevity was "cigarettes, whisky and wild, wild women.” Which doesn’t mean you should run out and buy a fifth of Jack Daniel’s just yet.

The 113-year-old World War I vet, believed to be the world’s oldest man, died on July 18 and will be buried today in Brighton, England. His obituaries describe the incredible sweep of his life: he breathed the air of three centuries, outlived his wife by 40 years, and flew on “motorized kites” made of linen and wire in battle against the German army.

The optimist’s worldview might capsize him in the face of life’s more difficult moments—optimists just don’t account for the usual grim possibilities.

Whenever someone lives as long as Allingham did, others are eager to learn his secret. Was it Allingham’s apparent freewheeling lifestyle that helped propel him to 113? It doesn’t appear so. According to researchers, it was probably the less adventurous side of his personality. Either that, or dumb luck.

Nowadays, the word personality has a more or less official definition in scientific circles, and researchers are fairly certain that particular personality traits can be directly linked to longevity. Psychologists use what is known as the “Big 5,” a paradigm designed to encapsulate any individual personality by ranking it on five different dimensions: agreeableness, openness, extroversion, conscientiousness and neuroticism. In theory, everyone falls somewhere on the spectrum of each of these traits.

Slowly but surely, there is a consensus emerging among researchers that two of these traits are consistently linked to how long we live. The first is conscientiousness, which entails a disposition to be diligent, organized, and responsible. The trait is measured according to the way in which a person responds to such statements as “I am exacting in my work,” or “I like order.”

In 1993, Howard Friedman, a professor of psychology at the University of California, took over an enormous longitudinal study called the Terman Life Cycle Study that consisted of approximately 1,000 subjects. Psychologists first assessed the personalities of these subjects in the 1920s. Then, some 60 years later, Friedman started tracking the surviving members of the group to figure out which “types” were still going strong.

Translating the results of the old personality tests into contemporary categories, he found that a disproportionate number of conscientious subjects were still alive in the 1980s. These findings make perfect sense—people who are more diligent and exacting in their daily lives can be expected to avoid certain pitfalls. Still, the findings were the first to establish a link between a stable childhood personality trait and survival decades into the future.

Somewhat less obvious were findings concerning the relationship between neuroticism and longevity. Neuroticism, in the context of these studies, is defined as a tendency to experience negative emotions, from anger to fear to run-of-the-mill anxiety.

In a study published by the Journal of Gerontology, Robert Wilson, at the Rush Institute for Healthy Aging, looked at 900 Catholic clergy members. He and his team assessed them according to the “Big 5” traits and followed them over the course of five years. Wilson found that the risk of death doubled in those with a neuroticism score in the top 10 percent. In other words, particularly neurotic clergymen and women were nearly twice as likely to die during the period in which Wilson followed them.

The neurotic life is, by definition, highly stressful. For physiological reasons, stress can be extremely damaging. It hinders the immune system, causes insomnia, and speeds the atrophy of the brain, to name a few. Neurotic people might also be less popular, adding further stress to an inherently stressful existence. From a physiological point of view, stress is stress.

But perhaps the most surprising finding of Dr. Friedman’s—who was working in California, of all places—was the curious relationship between cheerfulness and longevity. Defining cheerfulness as optimism plus a sense of humor, Friedman found his cheerful subjects lived relatively shorter lives in comparison to subjects with less sunny outlooks.

Why would this be? For one thing, Friedman speculates, optimists are less likely to react with appropriate caution to troubling health symptoms, assuming the best and moving heedlessly along. For another, the optimist’s worldview might capsize him in the face of life’s more difficult moments—optimists just don’t account for the usual grim possibilities.

So how do we explain Allingham’s super-human longevity? It probably wasn’t his drinking and smoking. Friedman goes on, “We found that the cheerful Terman children grew up to drink more alcohol and smoke more cigarettes.” It’s what he calls “illusory optimism”—a feeling that they’ll circumvent life’s harsh realities.

In that sense, it appears Allingham not only defied his statistical life span, but longevity science as well.

Casey Schwartz is a graduate of Brown University. She's working on a book about the brain world.