Smart people should thank their mothers because, according to researchers, their mothers are mainly responsible for transmitting intelligence genes. Thus, gender stereotypes that have survived for centuries are perhaps about to disappear. Single women who want an intelligent child don’t need to look for a Nobel Prize at the nearest sperm bank and it is likely that men will begin to see the intelligence of women as an important part of their attraction.
At the basis of this idea are found what are known as “conditioned genes”, that behave differently depending on their origin. Basically, these genes have a kind of biochemical tag which allows their origin to be traced and even reveals if they are active or not within the descendant cells. Interestingly, some of these conditioned 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 and 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 a 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, followed by many others over the years. In these studies the co-evolution of the brain and the conditioning of the genome was analyzed, leading to the conclusion that maternal genes contribute most to the development of the thought centers in the brain.
During the first experiment, researchers created embryos of rats that only had genes of the mother or of the father. But when it came 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 other hand, 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.
More 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 embryonic development, any cell can appear anywhere in the brain, but as the embryos mature and grow, cells that had paternal genes accumulate in some of the emotional centers of the brain: the 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 are developed the most advanced cognitive functions, such as intelligence, thought, language and planning.
New studies, new lights
Of course, scientists have continued to investigate this theory. Robert Lehrke, for example, revealed that most of a child’s intelligence depends on the X chromosome. He also showed that since women have two X chromosomes, they are twice as likely to transmit characteristics related to intelligence.
Recently, researchers at the University of Ulm, Germany, studied the genes involved in brain damage and found that many of these, especially those related to cognitive abilities, are found in chromosome X. In fact, it is no coincidence that mental disability 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 Glasgow, Scotland. In this study, 12,686 young people aged between 14 and 22 years were interviewed every year since 1994. The researchers took into account several factors, from skin-color and education to socio-economic status. They found that the best predictor of intelligence was the IQ of the mother. In fact, the young people’s IQ varied only an average of 15 points from that of their mothers.
Genetics is not the only factor
Besides genetics, we can also find other studies that reveal the mother plays an important role in the intellectual development of children, through 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 for playing complex symbolic games at the age of two years, are more persistent, and show less frustration while problem solving.
This because a strong bond gives children the security necessary to explore the world and the confidence to solve problems without losing heart. In addition, these mothers also tend give their children a higher level of support in 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. For seven years, these researchers analyzed the way mothers relate with their children. They found that when the mothers were emotionally supportive and adequately fulfilled their children’s intellectual and emotional needs, the hippocampus of the kids at age 13 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.
Of course, this not to say that the relationship with the father should not be as fully developed, just that because of our social structure, including some of the gender stereotypes that still remain, it is usually the mother that spends the most time with her small children.
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, stimulation and personal characteristics. 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, the limbic system also comes in to play, 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 that intelligence and nourish it throughout life with new challenges. Otherwise that intelligence will stagnate.
Despite what may be influenced by genetics, fathers should not be discouraged because they also have much to contribute to the development of their children, especially by 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.