A bright ten-year-old with brothers and sisters of average intelligence will suffer a five to ten point IQ disadvantage compared to a similar child with equally bright siblings.

London - The next time you raise an eyebrow at the views of your spouse, sibling or friend, keep in mind that they could be making you smarter.

For a study has found that stimulating households where people talk, make jokes and challenge each other can boost IQ levels by several points.

The research challenges the commonly held notion that our intelligence is fixed for life by the age of about 18.

Current scientific consensus suggests that cleverness is controlled by genes, with environmental factors such as schooling and nutrition playing a part up to this age. After this point, IQ scores stabilise.

But Professor James Flynn argues that people can “upgrade” their own intelligence throughout their lives – and the best way to do this is to marry someone cleverer, or socialise with bright friends.

The academic, who is the emeritus professor of political studies and psychology at the University of Otago in New Zealand, believes intellectual stimulation from others is crucial as the “brain seems to be rather like a muscle – the more you use it, the stronger it gets”.

However, the reverse is also true – so people who share a home or workplace with the intellectually challenged risk seeing their IQ levels nosedive as a result. Professor Flynn analysed US intelligence tests from the last 65 years and correlated the results with people’s ages. This enabled him to compile new IQ “age tables”.

He found the “cognitive quality” of a family alters the IQs of all members, especially the children.

It can “lift” or hold them back, depending on the gap between their brightness and that of their siblings and parents.

A bright ten-year-old with brothers and sisters of average intelligence will suffer a five to ten point IQ disadvantage compared to a similar child with equally bright siblings, the age tables revealed.However, children with a low IQ could gain six to eight points by having brighter siblings and special educational treatment.

Professor Flynn, whose book, Does Your Family Make You Smarter? comes out next month, also concluded that although genetics and early life experiences determine about 80 percent of intelligence, the remaining 20 percent is linked to lifestyle.

This means that people can raise their IQ, or allow it to fall, by ten points or more. He told The Sunday Times: “As you leave childhood behind, the legacy of your family diminishes but the game is not over – a large proportion of your cognitive quality is now in your own hands. You can change it yourself and your IQ can vary through life according to your own efforts.

“So even in your late twenties and beyond your IQ is very much your own – you can control it and upgrade yourself.

“So going through life feeling your childhood is holding you back is misunderstanding how much power you have to improve yourself.”

The psychologist is renowned for discovering a long-term increase in the intelligence of populations – a phenomenon called the Flynn Effect.

He demonstrated this began in 1930 and has resulted in an average IQ rise by three points a decade since.

The cause is believed to be related to a combination of factors including better education, nutrition and an increasingly complex world.

Daily Mail