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Smart people should thank their mothers because, according to
researchers, their mothers are responsible for the transmission of the
intelligence genes. Thus, gender stereotypes that survived over
centuries are perhaps about to disappear. Single mothers who want an
intelligent son don’t need to look for a Nobel Prize at the nearest
sperm bank and it is likely that men begin to re-evaluate the
intelligence of women.
At the basis of this idea there are those known as “conditioned genes”,
that behave differently depending on their origin. Basically, these
genes have a kind of biochemical tag which allows to trace the origin
and reveals even if they are active or not within the progeny cells.
Interestingly, some of these affected genes work only if they come from
the mother. If that same gene is inherited from the father, it is
deactivated. Obviously, other genes work the opposite, are activated
only if they come from the father.
Mother's genes go directly to the cerebral cortex, those of the father to the limbic system
We know that intelligence has an hereditary component, but until few
years ago we thought that much of it depended on the father as well as
on the mother. However, several studies revealed that children are more
likely to inherit intelligence from the mother, because intelligence
genes are located on chromosome X.
One of the first studies in this area was conducted in 1984 at the
University of Cambridge. This study analyzed the co-evolution of the
brain and the conditioning of the genome, to conclude that the maternal
genes contribute most to the development of the thought centers in the
brain.
During the study, researchers created the embryos of special rats that
only have genes of the mother or the father. But when came the time to
transfer them to the uterus of an adult rat, the embryos died. So it was
discovered that there are conditioned genes which are activated only
when inherited from the mother and that are vital to the proper
development of the embryo. On the contrary, the genetic heritage of the
father is essential for the growth of the tissue that will form the
placenta.
At that time, the researchers hypothesized that if these genes were
important for the development of the embryo, it was also likely that
they could play a major role in lives of animals and people, maybe they
could even result in some brain functions. The problem was how to prove
this idea, because embryos with genes from only one parent died quickly.
The researchers found a solution: they discovered that embryos could
survive if normal embryonic cells were maintained and the rest were
manipulated. This way they created several genetically modified
laboratory mice that, surprisingly, did not develop the same way.
Those with an extra dose of maternal genes developed a bigger head and
brain, but had little bodies. Conversely, those with an extra dose of
paternal genes had small brains and larger bodies.
Deeply analyzing these differences the researchers identified cells that
contained only maternal or paternal genes in six different parts of the
brain that control different cognitive functions, from eating habits to
memory.
In practice, during the first days of the embryo development, any cell
can appear anywhere in the brain, but to the extent that the embryos
mature and grow, cells that had the paternal genes accumulate in some
areas of the emotional brain: hypothalamus, amygdala, the preoptic area
and the septum. These areas are part of the limbic system, which is
responsible for ensuring our survival and is involved in functions such
as sex, food and aggression. However, researchers have not found any
paternal cells in the cerebral cortex, which is where they develop the
most advanced cognitive functions, such as intelligence, thought,
language and planning.
New studies, new lights
Of course, scientists continued to investigate this theory. Years later,
Robert Lehrke revealed that most of childrens’ intelligence depends on
the X chromosome, and he also showed that since women have two X
chromosomes are twice as likely to inherit the characteristics related
to intelligence.
Recently, researchers at the University of Ulm, Germany, studied the
genes involved in the brain damage and found that many of these,
especially those related to cognitive abilities, were on chromosome X.
In fact, it is no coincidence that the mental illness is 30% more common
in males.
But perhaps, one of the most interesting results in this sense comes
from a longitudinal analysis conducted by the Medical Research Council
Social and Public Health Sciences Unit in the United States. In this
study they interviewed every year since 1994, 12,686 young people aged
between 14 and 22 years. The researchers took into account several
factors, from the color of the skin and education to socio-economic
status. This way they found that the best predictor of intelligence was
the IQ of the mother. In fact, the ratio of young people’s intelligence
varied only an average of 15 points from that of their mothers.
Genetics is not the only responsible
If we leave genetics we can also meet other studies that reveal the
mother plays an important role in the intellectual development of
children, through the physical and emotional contact. In fact, some
studies suggest that a secure bond is intimately tied to intelligence.
Researchers at the University of Minnesota, for example, found that
children who have developed a strong attachment with their mothers
develop a capacity of playing complex symbolic games at the age of two
years, are most persevering and show less frustration during the
troubleshooting.
This because the strong bond gives the necessary security to allow
children explore the world and the confidence to solve problems without
losing heart. In addition, these mothers also tend to help the children
solving problems, thus helping to further stimulate their potential.
The importance of the emotional relationship for the development of the
brain has been demonstrated by researchers at the University of
Washington, who revealed for the first time that a secure bond and the
love of the mother are crucial for the growth of some parts of the
brain. These researchers have analyzed for seven years the way mothers
relate with their children and have found that when supported
emotionally their children and adequately gratified their intellectual
and emotional needs, at age 13 the hippocampus of the kids was 10%
greater than that of children of mothers who were emotionally distant.
It is worth mentioning that the hippocampus is an area of the brain
associated with memory, learning and stress response.
Can we really talk about hereditary intelligence?
It is estimated that between 40-60% of intelligence is hereditary. This
means that the remaining percentage depends on environment and
stimulation. In fact, what we call intelligence is nothing more than the
ability to solve problems. But the curious fact is that to solve
problems, even a simple mathematical or physical one, comes also into
play the limbic system, because our brain works as a whole. Thus, even
if intelligence is closely linked to the rational thinking function, it
is also influenced by intuition and emotions, that genetically speaking,
are influenced by the contribution of the father.
Moreover, we must not forget that even if a child has a high IQ, we must
stimulate his intelligence and nourish it throughout life with new
challenges which are constantly improving. Otherwise intelligence will
disperse.
Beyond what was stated by genetics, fathers should not be discouraged,
because they also have much to contribute to the development of their
children, especially being emotionally present. The IQ with which we are
born is important, but not decisive.
Sources:
Luby, J. L. et. Al. (2012) Maternal
support in early childhood predicts larger hippocampal volumes at
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breast feeding on intelligence in children: prospective study, sibling
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Zechner, U. et. Al. (2001) A high
density of X-linked genes for general cognitive ability: a run-away
process shaping human evolution? Trends Genet; 17(12): 697-701.
Keverne, E. B.; Surani, M. A. et.
Al. (2004) Coadaptation in mother and infant regulated by a paternally
expressed imprinted gene. Proc Biol Sci.; 271(1545): 1303–1309.
Vines, G. (1997) Mamá, gracias por la inteligencia. El Mundo; 253.
Keverne, E. B.; Surani, M. A. et.
Al. (1996) Genomic imprinting and the differential roles of parental
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