A touch of madness may be the key to greatness

Some of history's most celebrated overachievers have battled inner demons on their way to success.

Winston Churchill, the prime minister who led Britain during the Second World War, suffered from bipolar disorder.

A severe mental illness can be just as debilitating as a crippling physical condition, leaving the sufferer unable to hold down a job, a relationship or have any semblance of a normal life. One psychologist, however, believes that, far from being harmful, in mild form such conditions could hold the key to success in life - and he takes his cue from the countless exceptional people in history who have had to battle with inner demons.

Dr David Geary believes people such as the former British prime minister Winston Churchill, the composer Ludwig Beethoven and the horror writer Edgar Allan Poe show there is a link between mental illness and achievement. Each member of this exalted trio is said to have suffered from manic depression or bipolar disorder, the condition in which periods of elevated mood alternate with spells of depression.

"In most cases, full-blown bipolar disorder is pretty maladaptive, but having the disorder expressed in a mild state could confer benefits," says Dr Geary, a cognitive development psychologist at the University of Missouri who outlined his ideas in his book, The origin of mind: Evolution of brain, cognition and general intelligence. The reason, Dr Geary believes, is that during the "mild hypomania" they experience, manic depressives think more quickly, have more energy and are more creative. Confidence levels rise, social inhibitions disappear and the creative juices flow freely. "They can put things together in ways that other people wouldn't think of or would take them longer to do," he says.

This idea can be understood by making comparisons to chimpanzees. There is evidence, Dr Geary says, that human brains "run at a higher revs per minute" than those of chimpanzees and other primates. This is because humans evolved mechanisms for speeding up the processing of information. Hypomania, the theory goes, involves a further speeding up of the brain's functioning beyond the normal human capacity.

"It's a continuation of whatever evolved mechanisms are revving up the human brain - they are over-expressed with manic depression," he says. Just as the phases of hypomania can bring benefits, so can the down phases. If taken to extremes, ruminating about things can cause severe anxiety or depression. But if done a little, it can be "very helpful". "The depression phase can lead to a period of self-reflection and caution. Things can be scrutinised and looked at with a more critical eye," Dr Geary says.

"Humans have the ability to project themselves forward in time and to simulate different ways of coping with these situations. They can figure out strategies." The conditions may not improve the quality of life of those who have them, but it seems they can make them successful. To be an advantage, Dr Geary says the condition has to be combined with intelligence and an ability to control the disorder's effects during the down phases.

Often the people who benefit the most are the relatives of someone with a full-blown disorder. Such individuals, Dr Geary says, tend to be "over-represented among high-achievers". This explains why, in the modern world, the genes that predispose an individual to a mental disorder are not drummed out of the population by natural selection. While an individual might be disadvantaged by having many types of gene that make them likely to suffer a disorder, if they have a smaller number they could be better off than the average individual.

Attention deficit disorder is another condition with potential benefits, although it illustrates the extent to which advantages depend upon context. Hyperactive individuals react quickly to changes around them and could be at an advantage in combat situations, for example. The opposite would apply if the same person was in a classroom trying to find the solution to a problem. Then, says Dr Geary, there would be a "context mismatch".

This means that people with mild forms of mental disorders should be channelled into areas of life in which their special talents can be harnessed, according to Dr Raymond Hamden, a clinical and forensic psychologist at the Human Relations Institute in Dubai. Many such individuals can "think outside the box" in ways the rest of us cannot. "Sometimes people who suffer from abnormal psychological elements, whether schizophrenia or bipolar disorder, can have interpretations of life that are quite unique," Dr Hamden says.

"People can go into the fine arts or consulting for architectural design, for theatre or for scripts needed by various entertainers." While we can understand the benefits of being slightly off the wall in the modern world, things would have been different in the prehistoric environments in which humans evolved. After all, there cannot have been much demand for advertising gurus, television scriptwriters or design consultants thousands of years ago.

So what selective pressures caused the disorders to evolve back then? Dr Geary believes the qualities that can make people stand out now could also have been advantageous in times past. "The way to think about these things is that the more primitive times aren't quite as different as many people think," he says. "They might have been a good hunter or figured out how to plant better crops. For men a good predictor of marriage ability and reproductive success is cultural success. Extra energy, extra ability to think creatively probably would contribute to the ability to achieve cultural success in a range of societies."

Dr Geary says his ideas could have implications for how clinicians treat people with mental disorders. Given that some disorders can be "overexpression of what is a good", it would be a bad thing to completely get rid of the symptoms. Doing that could put the person at a disadvantage. "They are not ill, it's just they're out on the continuum a little bit too far," he says. "The treatment should bring them back along the continuum rather than switching them to a different category."

And where would Dr Geary himself like to be on the continuum? "That's a tough question. Certainly not too far out. Maybe a little bit out" [e-mail]