Everybody worries. Parents worry about their children, wives worry about husbands. Barack Obama must have worried for months about Hillary Clinton, and all of us are worried about the rapidly rising cost of food and fuel.

But is worry necessary? Traditional wisdom holds that whatever human beings do, it must be for good reason. We may not like worrying, but, so the theory goes, there must be some survival advantage in it.

Is this true? Maybe 10 per cent of what we worry about really matters; the rest is stuff that never happens (the sky is falling!) or already has happened so we can't do anything about it (losing money on the stock market). Studies show that people who worry a lot are generally less effective than those who don't; they get less work done and are often less happy. In experimental tasks, worriers are slower to respond than non-worriers (presumably because worrying burns off mental energy that would be more effectively applied elsewhere), and one recent laboratory study at Yale and Pennsylvania State University has shown that the mere opportunity to worry for five minutes is enough to bring down a person's mood.

Evolutionary products aren't that smart

Broadly speaking, it's a fallacy to presume that all of evolution's products are intelligently designed. Evolution has no foresight - and no hindsight, either. When it stumbles on a solution it tends to stick with it, even if that solution might be less than stellar.

Take, for instance, the human spine. We are stuck with a single-column spine, not because it is ideal but simply because evolution happened to stumble on a mediocre design and, once there, that design became entrenched. From the perspective of an engineer, our spine is clumsy and inelegant; it gets the job done, but hardly in the best way possible. In short, it is what engineers call a kluge. The brain circuits that lead us into worry, stress and anxiety may be similarly clumsy, circuits that are adequate, but with serious vulnerabilities.

At its most useful, worrying is about mobilising us for action. We recognise a threat - perhaps a predator in the distance - and our levels of cortisol, a hormone released in response to stress, rise and we prepare for fight or for flight.

The trouble is that evolution forgot to include an “off” button. Preparing for fight-or-flight makes sense when we're talking about ancestors who needed to decide how to deal with immediate threats such as predators, but not, for the most part, with the sort of persistent situations that drive modern human beings to distraction.

Most worry, at least today, isn't about immediate threat, it's about long-term threat. What will happen if I lose my job? Will my partner ever really love me? Such questions are worth consideration but are not the sort of thing that can be solved in an instant.

In these circumstances, elevated cortisol levels do us no good. The hormone primes our body for physical activity if we, say, have to sprint from danger. However, it also acts to dampen the immune system, which may make us susceptible to infections. What we really need to do is relax and think clearly, but evolution often leads us in the opposite direction; worry often breeds anxiety, paralysis, depression, rather than creative solutions. A recent study from University College London of 542 adults with an average age of 60, found that those who engaged with their problems and sought social support had lower cortisol levels than those who did not.

The word worry comes from a Middle English word “wyrgan”, which means to strangle. And that's what worries often do; they seize us by the throat until we can't think about anything else. When worry takes on a life of its own, it becomes a huge and often pointless drain on our time and energy. Worse, chronic worry may take a toll on our hearts. Earlier this year a study from Cambridge University linked banking crises to an increased number of heart attacks, perhaps because chronic worry and stress can lead people to drink more, smoke, eat too much and take less exercise.

Worry, it has been said, is often like a rocking chair: it gives you something to do, but it doesn't necessarily get you anywhere. Evolution may have given us the opportunity to worry, but that doesn't mean we should take the bait.

How to deal with worries

Worries largely fall into three groups: those that demand immediate attention (“alarm bells”); those that prompt us to focus on continuing problems; and those that anticipate future threats.

Alarm bells are serious business. If you see smoke and are worried about whether there is a fire, by all means drop everything and figure out what needs to be done.

Reminder worries, such as taking the children to their swimming classes or remembering to send Dad a card for Father's Day, should be left to a calendar; use computers or daily planners to offload anxiety.

Future problems deserve due consideration, but don't let them take over your life. Set aside a particular time each day to worry about long-term risks, such as financial difficulties and what you can do about them. Don't let yourself think about those issues at other times.

Prepare, but don't panic It's good to think ahead, but useless to worry about things beyond your control. Don't waste mental energies on problems you can't do anything about.

Become mindful Worry mostly comes from automatic, unmonitored thought. If you find yourself worrying about the same thing twice in a day, ask yourself if you are worrying about something you can change. If not, force yourself to move on. Think about something different.

Making decisions Don't kill yourself trying to make perfect decisions Every decision takes mental energy. It's OK to think long and hard about whether to get married, move to a new city, or to have a child, but when you're deciding between that Saab and a Volvo, don't give yourself more than a few days. Chocolate and vanilla are both nice and, in the final analysis, it won't matter which one you've eaten.

Gary Marcus is Professor of Psychology at New York University. His new book Kluge: the Haphazard Construction of the Human Mind (Faber, £15.99) is available at £14.39, free p&p, from Times Books First. Call 0870 1608080; timesonline.co.uk/booksfirstbuy

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