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.
A category of genes known as “conditioned genes” are thought to work only if they come from the mother in some cases and the father in other cases. Intelligence is believed to be among the conditioned genes that have to come from the mother.
Laboratory studies using genetically modified mice found that those with an extra dose of maternal genes developed bigger heads and brains, but had little bodies. Those with an extra dose of paternal genes had small brains and larger bodies.
Researchers identified cells that contained only maternal or paternal genes in six different parts of the mouse brains which controlled different cognitive functions, from eating habits to memory.
Cells with paternal genes accumulated in parts of the limbic system, which is involved in functions such as sex, food and aggression. But researchers did not find any paternal cells in the cerebral cortex, which is where the most advanced cognitive functions take place, such as reasoning, thought, language and planning.
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.
But mothers have also been found to play an extremely significant role in this non-genetic part of intelligence, with some studies suggesting a secure bond between mother and child is intimately tied to intelligence.
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.
A strong bond with the mother is thought to give a child a sense of security which allows them to explore the world, and the confidence to solve problems. In addition, devoted, attentive mothers tend to help children solve problems, further helping them to reach their potential.
Of course, there’s no reason why fathers can’t play as big a nurture role as mothers. And researchers point out that a whole array of other gene determined traits – like intuiton and emotions – which can be inherited from the father are also key to unlocking potential intelligence, so fathers – don’t despair.