Next time you raise an eyebrow at the views of your partner, friend, sibling   or colleague, remember they could be helping to make you smarter. New research shows that intelligence is not fixed but can be boosted throughout adulthood by family members, bright mates and intellectually stretching   careers. The study challenges the commonly held belief that intelligence is static by the age of about 18. Current scientific consensus suggests that intelligence is controlled by genes, with environmental factors such as schooling and nutrition playing a partial role up to this age. After this point, IQ scores stabilize  . But James Flynn, professor of political studies and psychology at the University of Otago in New Zealand, argues that people can "upgrade" their own intelligence throughout their lives. He 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 opposite is also true - so people sharing a home or workplace with those who are intellectually challenged risk seeing their IQ levels fall as a result. He found the "understanding quality" of a family changes the IQs of all members, especially children. It can "lift" or hold 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. However, children with a low IQ could gain six to eight points by having brighter siblings and special educational treatment to help pull them up. Professor Flynn 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. Therefore, the best way to boost IQ level is to mix with bright friends, find an intellectually challenging job and marry someone cleverer. James Flynn holds the belief that   _  .
intellectual stimulation from others makes the brain work better people should avoid working with those intellectually challenged one's IQ could be held back if he has bright brothers or sisters the IQ of children is least influenced by the understanding level of a family