Next time you raise an eyebrow at the views of your partner, friend, brother, sister or colleague, remember they could be helping to make you smarter. New research shows that intelligence (智力)is not fixed but can be improved throughout adulthood by family members, bright mates and intellectually challenging careers. The study challenges the commonly held belief that intelligence is fixed by the age of about 18.

Scientific consensus (共识)suggests intelligence is controlled by genes, with environmental factors (因素)such as schooling and nutrition playing a part up to this age. After this point, IQ scores remain unchanged. But James Flynn, professor at the University of Otago in New Zealand, argues that people can "upgrade" their intelligence throughout their lives. He believes intellectual stimulation (刺激)from other people is important as the "brain seems to be rather like a muscle --the more you use it, the stronger it gets". So people who share a home or workplace with the intellectually challenged risk seeing their IQ levels nosedive as a result.

Professor Flynn analyzed US intelligence tests from the last 65 years and created new IQ "age tables". He found 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 brothers and sisters. However, children with a low IQ could gain six to eight points by having brighter brothers and sisters and special educational treatment to help pull them up.

Professor Flynn concluded that although genetics and early life experiences determine about 80% of intelligence, the remaining 20% is linked to lifestyle. This means people can raise their IQ, or allow it to fall, by ten points or more.

He suggests the best way to improve IQ levels is to socialize with bright friends, and find an intellectually challenging job.