Determining which of your children's traits come from which side of the family is a classic parenting pastime. On everything from eye color to IQ, one parent is likely to claim, “He/she got that from me!”
Now, research suggests that when it comes inherited intelligence, mom may deserve more credit than dad.
As the Independent reports, children are more likely to receive genes related to intelligence from their mother than their father. The scientists behind these studies say that because intelligence genes are carried on the X chromosome (women carry two X chromosomes and men have only one), moms have a higher chance of passing on those genes to any offspring.
Moreover, some scientists theorize that intelligence might be a “conditioned gene,” meaning that it only works if it comes from a specific parent (in this case, the mother).
The research behind these findings comes from an experiment with genetically modified mice. In that study, mice that received an extra dose of maternal genes had larger brains and smaller bodies. In contrast, mice that got an extra dose of paternal genes generally had larger bodies and smaller brains.
Additional research not dependent on rodent brains includes a 1994 survey of more than 12,000 young (human) adults. Controlling for factors such as education and socio-economic factors, researchers found that the mother's IQ remained the best predictor of a child's intelligence.
However, some have pointed out the inherent flaw in using these findings as proof that a kid's cleverness comes from mom. Writing in Forbes, science writer and biology professor Emily Willingham criticizes the assumption that the double-X chromosome gives women a greater chance of passing on intelligence, saying that genes don't work that way. She writes:
“Whatever is on the X can pass from mother to child or father to (usually) daughter, but the two X chromosomes the mother has aren’t the same and don’t at all automatically double the odds of inheriting a specific variant.”
Willingham goes on explain that even inheriting two X chromosomes from your genius mother might not guarantee a sky-high IQ, as each cell will “turn off” most of one X or the other. Moreover, she says the “conditioned” genes belonging to mom also require complementary conditioned genes tagged by dad for proper development.
Both sides agree on one thing—human intelligence is complex and no matter who it comes from, genetic inheritance is only part of the story. According to Yahoo! News, as much as 40-60% of intelligence comes from environmental factors. However, this is another area where mom plays a significant—and more visible—role.
Researchers at Washington University studying preschool depression found that children of attentive mothers had a larger hippocampus than those whose moms were more distant. Moreover, children who had a strong bond with their mothers are thought to be more confident, more equipped to solve problems, and more likely to reach their potential.
This doesn't mean that fathers haven't also been found to play an important role in fostering children's intellectual development. According to Science Daily, a study from the University of North Carolina at Chapel Hill found that fathers had a bigger impact on preschool children's language development than mothers.
In other words, when it comes to raising a smart child, what happens after he or she is born may be as important as genetics. As Willingham writes in Forbes, there's a lot more to intelligence than chromosomes:
“It’s layer upon layer upon layer of interacting pieces. So no. Not just your mother. Not just the X chromosome. Not even just genes.”