This week’s guest blogger – John Farndon studied earth sciences at Cambridge University and has written more than 300 books on science and nature including How the Earth Works, The Wildlife Atlas, The Practical Encyclopedia of Rocks and Minerals, and the forthcoming The Atlas of Oceans. He also writes extensively on the history of ideas and contemporary and environmental issues, penning such books as China Rises, India Booms, Bird Flu and 101 Facts You Should Know about Food. He was the author of the best-sellers Do Not Open, Do You Think You’re Clever? and The World’s Greatest Idea and his books have been translated into most major languages. He has been shortlisted four times for the Royal Society Prize for Science Books, and for the Society of Authors Education Award. He lives in London.

In a fortnight’s time, I’m giving a talk at the Brighton Science Festival about a recent book of mine entitled ‘The World’s Greatest Idea”, which is an exploration of 50 of the great ideas that have shaped the world.

One of the ideas that features is the welfare state, and in researching the topic I was reminded how groundless assumptions can assume the mantle of ‘common sense’ if repeated enough times.

Currently, many governments around the world are wondering how to cut welfare budgets. Generous spending on welfare is not only unaffordable in these hard economic times, it is argued; it is a drag on economies, discouraging people from seeking work. And most people assume this is so.

And yet this ‘common sense’ argument has no actual foundation in reality. Welfare systems have rarely acted as a brake on a country’s economy. In nearly all cases, countries that have introduced a welfare system have experienced dramatic economic growth.

After Germany introduced its welfare system in the 1880s, its economy grew rapidly – so rapidly that Britain was shocked to find it had an economic rival for the first time, and right on its doorstep. And in the post-war years, Western Europe has experienced a time of unparalleled prosperity. Moreover, the most prosperous countries, such as Sweden and Germany, are those with some of the most generous welfare provision.

Similar myths have been perpetuated in the field of science. Do you, for instance, assume that it is scientifically proven that intelligence declines slowly with age? If so, you’re not alone. For a long while, IQ tests did appear to show that younger people did better than old people, and were taken as gospel proof that intelligence declines with age. Yet a re-examination of the evidence shows that this isn’t so for two reasons.

The first was that the IQ tests which showed young people did better were simply a matter of training. Younger people had had more practice of doing the kind of mental tasks tried in IQ tests than older people. As soon as older people were trained in this kind of thinking, their performance levels shot up.

The second reason is that IQ tests were done against the clock. If the time pressure is removed, older people do just as well as their young counterparts – and it is quite reasonably argued that older people are slower simply because their experience means they have to sift through more possibilities to reach the answer.

In fact, these assumptions about IQ and age went further. Psychologists have been telling us for decades that the one thing that your IQ is fixed and unchangeable through life. If you’re intelligent, we were told, you remain intelligent until age begins to sap it. If you were not, you were not, and that was that. Yet there is little scientific evidence that any of this is so. It is just another ‘common sense’ assumption. And recent scientific research has begun to throw doubt on this.

It is now becoming clear, for instance, that IQ is closely connected to your working memory, the amount of current data you can store in your head at any one time. Recent research by Torkel Klingberg in Sweden showed that the neural systems used in working memory may actually grow in response to training. What’s more children who completed a training course not only did better in the tests given to them by Klingberg but actually found their scores in IQ tests leap by 8 per cent.

Of course, Thomas Kuhn argued that scientists can never divorce their own personal take on their subject, and that science is inevitably bound within the prevailing outlook. So there is always likely to be a time when any assumption is finally shown to be false. But in the meanwhile it definitely pays to be wary of those who would dismiss your questions on the basis of common sense.

As Einstein observed, “Common sense is the collection of prejudices acquired by the age of 18.”