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No, children don’t ‘inherit intelligence’ from mother’s X chromosome

This article is more than 5 years old

An image of what seems to be a newspaper clipping with the headline “Children inherit their intelligence from their mother not father” has been circulating for some time on social media.

It’s been posted on Facebook in South Africa, and shared more than 263,000 times. The article claims that a mother’s genetics determine how clever her children are. The father makes no difference.

“Women are more likely to transmit intelligence genes to their children because they are carried on the X chromosomes and women have two of these while men only have one,” the article reads.

It says “scientists” believe the genes for advanced cognitive function 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. Intelligence is believed to be among the conditioned genes that have come from the mother.”

Tellingly, the article doesn’t give its sources, simply crediting its claims to “researchers” and “scientists.”  

‘Logic behind statement deeply flawed’

Africa Check asked Prof David H Skuse,  author of the paper X-linked genes and mental functioning, about the claim. Skuse heads the behavioural and brain sciences unit at the Institute of Child Health in London, UK.

He said X-linked genes are linked to brain development – but not intelligence. And women get one of their two X chromosomes from their father.

“Whilst it is true that X-linked genes are relatively highly specialised for brain development relative to other genes from the rest of the genome, that does not equate to intelligence,” he told Africa Check.

“Only one X chromosome is active in each cell of the female, despite her possession of two X chromosomes, and one of the X chromosomes comes from the father! Males get their single X from the mother of course. The logic behind this statement seems to be deeply flawed,” he said.

‘Inherited intelligence from many genetic variants’

Human females have two X chromosomes (XX) and males have a single X and a single Y chromosome (XY) – as do all other mammals.

The claim has been debunked by science journalist Dr Emily Willingham in the Forbes article No, Research Has Not Established That You Inherited Your Intelligence From Your Mother.

“Let’s get this out of the way: Intelligence is complicated,” she writes. “While maybe half of our intelligence as we currently define and measure it is inherited, that proportion is in turn fractured into many many genetic variants scattered across our genomes.”

Extra X-linked variants may be shut down

She explains that mothers pass on one X chromosome to their children, and fathers pass on either an X (to a daughter) or a Y (to a son).

And only one X chromosome is genetically active in female cells.

“Mothers do tend to have two X chromosomes, but they aren't identical chromosomes, and of course, they got one of them from their fathers. Mothers generally pass only one X to their children and those children in turn receive the second sex chromosome (X or Y) from their fathers.

“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.”

According to her, inheriting an X-linked gene variant is not a guarantee that it will be used because they may be deactivated.

“The doubled ‘gene dosage’ for people with two (or more) X chromosomes is adjusted downward in a clever way: each cell turns off most of one X or the other. So inheriting an X-linked gene variant isn't a guarantee that it will even be used because some cells might just shut it down.”

A complex trait

In earlier research by Africa Check, professor of metabolic medicine Fredrik Karpe told us that measured smartness of kids is even more determined by cultural, economic and social environment factors.

The claim has also been checked by Snopes and found to be unproven.

Intelligence is a complex trait, influenced by many different genetic and environmental factors. It isn’t simply “inherited” on the X chromosome. 

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