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The only guideline offered to mental health professionals in distinguishing between mania and hypomania is “degree of severity.” Hypomania is “not sufficiently severe to cause marked impairment in social or occupational functioning or to require hospitalization.” But DSM-IV tells us little else, when there is so much more that could be said.

This relative neglect of hypomania by psychiatry is striking when we consider that it affects many more people than does mania. We know from numerous large-scale studies, replicated both nationally and internationally, that classic manic depression exists in slightly less than 1 percent of the general population.10 A notably smaller but growing amount of literature on hypomania suggests that 5 to 10 percent of the population is hypomanic.11 Whatever the exact percentage, psychiatry’s most recent discovery is not a rare expression of bipolar genes, but its most common form.*

That hypomania is so much more common than mania may give us a crucial clue to its genetic function and evolutionary importance. Mania, according to one school of thought, is a disease like sickle-cell anemia.12 Sickle-cell anemia is a blood disease that primarily affects people of African origin. To contract the disease, you must inherit the recessive sickle gene from both your mother and your father. Far more often, people inherit only a single sickle gene from one parent; epidemiologists call these people “carriers” because they carry the gene without manifesting the illness. As it turns out, they are much more than that. They are the reason the gene exists. A single sickle gene greatly enhances resistance to malaria, a deadly disease prevalent in Africa. This gene has been favored by natural selection, even though it causes a deadly disease, because it saves more people than it kills.

We have not isolated one singular manic gene. Investigators at the Department of Psychiatry at Johns Hopkins University Medical School, where I teach, and at other institutions around the world, have homed in on half a dozen genes associated with mania.13 Though the numbers may be more complex, the same principles may apply: a less probable combination of genes produces the undesirable disease of mania, while a more frequent combination produces the advantageous outcome of hypomania. It could be that quantitatively more hypomanic genes are required to produce mania. Call this the slot machine model. Three cherries produces a moderate payout: hypomania. But once in a great while you get five cherries, and you’re flooded with coins: mania. Alternatively, there may be a specific gene that needs to be combined with hypomanic genes to produce mania. Raymond DePaulo, James Potash, and their colleagues at Johns Hopkins have found a gene that mania and schizophrenia share in common—a possible “psychoticism gene.” Mania might be the result when one is unlucky enough to inherit both hypomanic genes and the psychotic gene.14

The story of the CEO father and his hospitalized son helps us understand why hypomanic genes exist. Relatives of manic patients, who have high rates of hypomania, have consistently been found to be far above average in income, occupational achievement, and creativity.15 Hypomania gives them an edge over the competition.

If there is any one trait that distinguishes highly successful people, it is that they are, by temperament, highly motivated. From our studies of the brain we now know that mood is an intrinsic part of the apparatus that controls motivation. Mood is meant either to facilitate or inhibit action. When someone is depressed, he has no motivation to act. What’s the point? Nothing seems worth doing, he has no energy to do it, and it probably won’t work anyway. Hypomania is the polar opposite. The drives that motivate behavior surge to a screaming pitch, making the urgency of action irresistible. There isn’t a minute to waste—this is going to be huge—just do it!

This pressure to act creates overachievers, but it also leads to impulsive behavior (ready, shoot, aim) and confident leaders who glibly take their followers over a cliff. Depending on how you look at it, the Internet phenomenon was either an exciting breakthrough of human ingenuity or a colossal error in judgment that forces us to ask: What were we thinking? In truth, it was both. The paradox of the hypomanic edge is that it is a double-edged sword.