New research shows that intelligence is not fixed but can be boosted throughout adulthood by family members, bright mates and intellectually stretching careers.

一项新研究显示，智力不是固定不变的，而是在整个成年期都会受到影响，家庭成员、聪明的配偶以及拓展智力的职业都会促进智力的提高。

Stimulating households where people talk, make jokes and challenge each other can boost IQ levels by several points, as can jobs that mentally energise employees.

The study challenges the commonly held notion 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 part up to this age. After this point, IQ scores stabilise.

But James Flynn, Emeritus 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 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.