Older fathers and the IQ of their children

By Razib Khan | September 20, 2013 2:53 am

From what people tell me IQ is a social construct which is totally controlled by environmental variables, and so is not of much interest. But curiously the other day when I looked at the hits on this website over the past 3+ years a huge number of highly accessed posts had to do with intelligence and IQ. In any case, seeing as how many readers of this weblog are having, or going to have, children at a relatively advanced age (in an evolutionary sense) I thought this post would be a good public service announcement. Below is a figure from a preprint posted on arXiv, The effect of paternal age on offspring intelligence and personality when controlling for paternal trait level (via Haldane’s Sieve):


I’m assuming that there’s initially an upward slope because more intelligent men tend to reproduce later (you can confirm this by looking at AGEKDBRN and WORDSUM variables in the GSS). Once you control for education and IQ the effect disappears. But there isn’t a downward slope, which you might predict if the hypothesis of increased mutational load was valid. IQ is a high polygenic trait with variation controlled likely by thousands of genes, but one would presume that large effect de novo variants could change that architecture.

As always, more data is welcome.

CATEGORIZED UNDER: Behavior Genetics, Psychology
  • phanmo

    I’m about to become a father at the age of 38 so this subject interests me immensely.

  • AG

    The chart worths lots of words

  • K_Ismail

    Very nice article! we really need to know about this!

  • Dmitry Pruss

    Those very few people on the chart born past 50 but they were all below the line, which is probably not significant both in statistical sense and in common-sense. (There are other significant drawbacks in having children very late, especially twins which were subject to this study). The magnitude of the age effect in the “more reasonable” paternal age bracket seems to be too small to measure ergo too small to bother.

    Note however that 2/3rds of IQ measurements were taken at the age of 11 when the environmental/nurture effects on intelligence are still strong. To evaluate the genetic component of the paternal-age effect without compounding nurture effects, it would have been better to use adulthood IQ values.

  • Dylan

    I’d guess there’s a lot of interesting themes that could be gleamed from this data. The gist of the trend lines is that older fathers have smarter children, but only because smarter and more educated fathers have children later at an older age. I’d like for that to be wrong. Is there really a defined relationship between IQ and education and then IQ and paternal IQ that you are able to adjust for them accurately? Also, the lines depend on a linear progression of IQ, which may or may not be the case.

    • Ruben C. Arslan

      I don’t know what you mean exactly by “defined relationship”, but in the paper we show that we did not only consider linear associations. We looked at this from a variety of methodological angles and all results were consistent with the gist you describe above.

  • redzengenoist

    “Once you control for education and IQ the effect disappears. But there isn’t a downward slope, which you might predict if the hypothesis of increased mutational load was valid. ”

    Well, there is a downward slope, it’s just not significant.

    • Ruben C. Arslan

      That is correct. However, if you check out Figure 2 or Table 3 (pages 18,19) you’ll see that the point estimate was just -0.02 [-0.07; 0.03] after we controlled for birth order (this correction is not shown in the figure Razib posted because it would’ve cluttered the graph too much). That is pretty close to zero. If we had to bet, my bet would still be on a tiny negative effect. Maybe larger samples would enable us to see closely, but there is what Meehl called the “crud factor” to consider (http://www.tc.umn.edu/~pemeehl/144WhySummaries.pdf).

  • andrew oh-willeke

    I would be curious to see how developmental disorders are treated in the studies. Most of the expected effect on IQ from advanced paternal age is associated with autism or congenital defects like chromosome number anomalies that create a much larger than average pool of developmentally disabled (aka retarded) children, without necessarily much of an effect on otherwise normal kids.

    It isn’t clear to me that the methodology used would fully capture that effect.

    Likewise, in personality, the major effect expected is elevated rates of particular psychosis conditions, rather than a shift in ordinary range personality.

    • Ruben C. Arslan

      The preprint is open access, so you can just check it out :-) Developmentally disabled kids etc were screened out of our sample, we were interested in explaining variation in the normal, nonclinical range. That variation is also highly heritable and linked to fertility and mortality, so an effect that just explains extreme cases would leave this heritability to be “missing” (not the best term, but you know what I mean).
      If you’d like to know more about different types of mutations and their parental origin and age biases (including e.g. trisomies, carriers of which were not in our sample) I recommend Campbell & Eichler 2013.

      We did find an effect on absorption, that might reflect previously reported associations with psychosis, but in the normal range, but it was not very robust either and we didn’t predict it, thus interpreted it with caution.

  • InfinityBall

    Speaking as a tactless Aspie, maybe you shouldn’t have pointed this out in direct response to a soon-to-be old father

  • Paul Conroy

    Ruben, it’s great to see you comment here!

    I’m an older father, I have 3 kids, born when I was 40, 46 and 48. My educational level is not high (undergraduate in Comp Sci, 3.86 GPA), my IQ is high (157). The mother of my eldest has IQ 135, and my eldest (daughter) is in the gifted program at school, the mother of my second and third has IQ 130, my second (son) had a diagnosis of PDD-NOS and more recently ASD, and has just started a new program in Brooklyn for Gifted kids with ASD, my third (daughter) seems like she will be the brightest of the 3 kids.

    I scanned your paper and didn’t see how you accounted for abilities of the father in particular, as education attainment is a poor proxy for intelligence, it’s a better proxy for conscientiousness. Also, I didn’t see anywhere you checked if father’s themselves are ASD? I have no diagnosis of ASD myself, but score very highly on Autistic/Asperger tests, well into the Autistic range. I also have other characteristics of ASD types, like I scored extremely high on the Ravens Progressive Matrices test (1 incorrect answer out of 150 or 200 questions, and test completed in a little over half the allotted time), similar to Temple Grandin who had a perfect score and finished early. I also have near perfect facial recognition and recall, and can recognize anyone I’ve ever met before, despite the passage of decades. I recently read an article – http://www.biologicalpsychiatryjournal.com/article/S0006-3223(13)00621-5/abstract – that seems to link superior Math ability in ASD people to the utilization of the “facial recognition” area of the brain in decomposing problems. So it may be that I have an ASD-type brain wiring.

    So my point is, if you don’t adequately account for ASD in fathers, then linking their children’s ASD to advanced paternal age may be spurious. My own theory is that ASD father’s mature later, and so have kids later in life.

    To my way of thinking, ASD can be characterized as a slower development trajectory than normal, so ASD people reach development milestones later than normal. I should also point out that based on 23andMe results, my youngest daughter has MORE of the known ASD causing SNP’s than my son, the difference is that she is female. Both daughters are more logical, assertive and systematic and less emotional and emphatic than their female peers – neither would be classified as ASD, but I think this is where the “missing” ASD girls are – they simply have a more masculine brain and are viewed by today’s society as more “you go girl”, than being labelled as problematic, but objectively compared to their peers, they would be ASD.

    • Ruben C. Arslan

      Congratulations on your and your families’ abilities :-)
      However, there seems to be some confusion here. We controlled for both parents’ IQs, not only education, thereby probably addressing your concern.
      It is however not true that educational attainment is a better proxy for conscientiousness than intelligence.

      The ASD results you refer to were studies by other researchers that I only cited (quite extensively since the research on ASD is spearheading molecular genetic techniques related to mutation). I can tell you that these studies employed simplex samples in which no close blood relative of kids with autism had autism spectrum disorders.

      I cannot speak to the merit of your own theory about ASD as this is not my area.

      • Paul Conroy

        Ruben,

        Thanks for the reply.

        For education attainment, above an IQ threshold, say 115-130, the remainder is conscientiousness. So high educational attainment does not equate to high IQ, as for instance the average PhD in English has an IQ of only around 115.

        In terms of “no close blood relative of kids with autism had autism spectrum disorders” – was that via self reporting, or were these fathers/parents actually objectively tested as part of the study?

        Also, its becoming very problematic to figure out which kids, who have an ASD diagnosis, actually have ASD symptoms. I watched a documentary the other night on an inner city ASD program, and a few of the “ASD kids” clearly suffered from Down’s Syndrome and a few other were just gravely mentally impaired, but today there is less stigma at the lower IQ level to be labelled Autistic or ASD, rather than retarded. Meanwhile at the higher IQ level, parents in places like New York, who have bright kids, who do not qualify for Gifted programs, desperately try to get them into ASD programs, as in both cases the education is normally free, and better than basic public school education. Both these proclivities are driving up the “mis”-diagnosis of ASD.

        Cheers,
        Paul

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About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at http://www.razib.com

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