A mother’s genetics determines how
clever her children are, according to researchers, and the father makes no
difference. 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. Scientists now believe genes for advanced
cognitive functions that 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. Studies using genetically modified mice found 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’s
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 where functions such as
reasoning, thought, language and planning take place. Researchers in Glasgow found
the theories extrapolated from mice studies bear out in reality when they
interviewed 12,686 people between the ages of 14 and 22 every year from 1994. The
team found the best predictor of intelligence was IQ of the mother. However,
the research also makes it clear that genetic are not the only determinant of
intelligence – only 40 to 60% of intelligence is estimated to be hereditary.
