Women are more likely to transmit intelligence genes to their children because they are carried on the X chromosome and women have two of these, while men only have one.
But in addition to this, scientists now believe genes for advanced cognitive functions which are inherited from the father may be automatically deactivated.
Concerned that people might not be like mice, researchers in Glasgow took a more human approach to exploring intelligence. They found the theories extrapolated from mice studies bear out in reality when they interviewed 12,686 young people between the ages of 14 and 22 every year from 1994. Despite taking into account several factors, from the participants education to their race and socio-economic status, the team still found the best predictor of intelligence was the IQ of the mother.
However, research also makes it clear that genetics are not the only determinant of intelligence – only 40 to 60 per cent of intelligence is estimated to be hereditary, leaving a similar chunk dependent on the environment.
Researchers at the University of Washington found that a secure emotional bond between a mother and child is crucial for the growth of some parts of the brain. After analysing the way a group of mothers related to their children for seven years, the researchers found children who were supported emotionally and had their intellectual needs fulfilled had a 10 per cent larger hippocampus at 13 on average than children whose mothers were emotionally distant. The hippocampus is an area of the brain associated with memory, learning and stress response.