According to this paper: Intelligence and the X chromosome by Gillian Turner, published by The Lancet (a highly regarded medical journal) in 1996, the X chromosome is dominantly responsible for coding "intelligence" and "intellectual function". Since a son inherits the X chromosome only from his mother, supposedly his intelligence is dominated by his mother's genes. At the closing paragraph the paper boldly claims (I added the bold and italic for emphasis):

In day-to-day practical evolutionary terms for our new millennium the male needs to remember that his primitive urges in mate selection are coded in his genome, and that they target current ideals of sexual attractiveness and youth. His frontal cortex should interpose reminding him that his sons’ intelligence, if that is important to him, is solely dependent on his partner, and that is mirrored in both her parents.

I am naturally skeptical of such sweeping claims. Has there been a follow up research to confirm, reject, or qualify this claim? (it's been almost 2 decades since the original paper) Is this conclusion commonly accepted by biologists?

A quick search found that this claim is repeated in the media and people's blogs, for example:

1 Turner, G. (1996). Intelligence and the X chromosome. The Lancet, 347(9018), 1814-1815. [pdf]

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    I have reopened this question based on 4 community reopen votes, and closed other, similar questions as duplicates pointing here as this seems like the most comprehensive question on the subject. Clearly people are interested in this - its been asked in various guises many times – Jamiec Sep 8 '16 at 10:45
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    An idea for a new study. Does your intelligence follow your mother's intelligence because you were raised by a stay-at-home mom for your first 5 years? Does intelligence follow the father for those raised by a stay-at-home dad in their first 5 years? And, going further, what happens to those with two working parents growing up in day-care during their first 5 years? Are some day-care centers called "Little Einstein" for any real reason? – GEdgar Sep 8 '16 at 17:01
  • I have asked a similar but different question at biology.SE, at here – Graviton Sep 9 '16 at 5:13

No, this grossly summarised version of the paper overstates its conclusions.

The quoted media reports suggest that the mother's genes account for all of the (variation) in intelligence of male children. They echo the statement you quoted from the final paragraph of the paper, but this final paragraph summary is an overstatement of the argument put forward in the paper.

Quoting from the second paragraph of the Turner paper:

Several studies on monozygotic twins reared apart show a correlation in adult intelligence quotient (IQ) values of about 0.7 "indicating that about 70% of the observed variation in IQ ... can be attributed to genetic variation".

No matter what the facts are about the main thrust of the paper - whether the mother's genes contribute more than the father's genes to the variation in their son's intelligence - it is clear that the mother's genes cannot account "solely" or "almost exclusively" for intelligence, because combined the parents' genes only account for 70% of the variation.

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    Not to be a party pooper, but the implied claim as I understand it is not arguing on the portion of intelligence that is determined by genes so much as the relative contributions of mother's versus father's genes. Hence, when I read the claim I assume they are speaking only of that portion of intelligence attributable to inherited genes -- nature -- without making any claims on environment -- nurture. Hence, I do not believe this response answers the question, even if it does provide background for those unfamiliar with discussions on the source of intelligence. – Michael Sep 8 '16 at 14:39
  • @Michael: This question was originally unclear, but has been influenced by edits, comments and duplicate questions. The final question that was decided on is not about the thrust of the Turner paper, but one poorly worded line of that paper that some people blew up into an extreme claim. This answer addresses that extreme claim. I think you are talking about a more interesting issue, but not the one this question is about. – Oddthinking Sep 8 '16 at 15:23
  • @Oddthinking 70% of the variation. If the variation is, say 10 IQ points, the genes of the mother count for 7 IQ points which is 7% of the overall IQ score (more or less, based on the average of 100 IQ). – Sklivvz Sep 11 '16 at 9:56
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    A separate issue that upsets me about this claim is that it only explains 70% of the variance found in subjects with enough intelligence to survive to take the test. Consider all the blastocysts that spontaneously aborted because the father's DNA was fatally flawed? Isn't some of the credit for an intelligent son due to the father providing DNA of adequate quality for survival? Perhaps apportioning credit between the parents is actually a meaningless endeavour. – Oddthinking Sep 11 '16 at 10:09
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    @Sklivvz: My understanding: If I tell you nothing about subject A, you can say "well, I don't know their IQ, but I can draw a bell-shaped curve describing the distribution of IQs, and calculate the variance of that curve." If I told you absolutely everything about subject A (genes + environment) you could hypothetically have an ideal model that predicts their IQ precisely - no variance. The claim here is that if you only know their genes, the best the model can possibly do is describe a distribution that has 30% of the variance of the naive model. The rest is caused by environmental factors. – Oddthinking Sep 11 '16 at 14:07

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