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. Robert Lehrke, for example, 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.
Luby, J. L. et. Al. (2012) Maternal support in early childhood predicts larger hippocampal volumes at school age. Journal of Proceedings of the National Academy of Sciences; 109(8): 2854–2859.Der, G. et. Al. (2006) Effect of breast feeding on intelligence in children: prospective study, sibling pairs analysis, and meta-analysis. BMJ; 333(7575): 945.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.
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.
Gécz, J. & Mulley, J. (2000) Genes for Cognitive Function: Developments on the X. Genome Res; 10: 157-163.
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 genomes in brain development. Brain Res Dev Brain Res; 92(1): 91-100.
Keverne, E. B. et. Al. (1996) Primate brain evolution, genetic and functional considerations. Proc. R. Soc. Lond. (Biol); 264: 1-8.
Allen, N. D. et. Al. (1995) Distribution of parthenogenetic cells in the mouse brain and their influence on brain development and behavior. Proc Natl Acad Sci U S A. ; 92(23): 10782–10786.
Surani, M. A.; S. C. Barton & M. L. Norris. (1984) Development of reconstituted mouse eggs suggests imprinting of the genome during gametogenesis. Nature; 308: 548–550.
McGrath, J. & Solter, D. (1984) Completion of mouse embryogenesis requires both the maternal and paternal genomes. Cell; 37(1): 179-183.
Barton, S. C.; Surani, M. A. & Norris, M. L. (1984) Role of paternal and maternal genomes in mouse development. Nature; 311:374-376.
Matas, L.; Arend, R. A. & Sroufe, L. A. (1978) Continuity of adaptation in the second year The relationship between quahty of attachment and later competence. Child Development; 49: 547-556.
Lehrke R. (1972) A theory of X-linkage of major intellectual traits. Am J Ment Defic; 76: 611-619.
source: Psychology Spot