Sci + Society,

#158: You Got It From Your Mama: Intelligence & Genetics

December 09, 2016

How much of your intelligence is inherited?  Which is more important: nature or nurture?  Smoking during pregnancy results in dumb babies…  right?

We answer all these questions and more in Episode 158.  Geoff Der, Senior Research Fellow at the University of Glasgow, joins Jesse to talk about the genetic link between parental intelligence and children’s cognitive development.

Nature vs Nurture

It’s an old debate, and one that won’t be entirely settled here.  But Der’s research can shed some light.

Probably the most striking finding from crunching huge amounts of data (we’re talking millions of data points here) is that many of the maternal behaviors we thought caused decreased intelligence, don’t.  Instead, it’s the mother’s own intelligence (or lack thereof) that is passed on to her offspring.

Example:  women who smoke while pregnant have children with impaired cognitive ability. But is it the smoking that causes this drop?  Or are less intelligent women more likely to smoke, and then pass on those genes to their kids?

We’re about to turn conventional wisdom on its head.  After crunching the numbers, it turns out that at least half of the variation in cognitive outcome is due to the mother’s own intelligence, not the smoking.  What’s more:  maternal education level completely accounts for the relationship between smoking during pregnancy and the child’s cognitive ability.  Once you take education level into account, there is no statistical significance between maternal smoking and cognitive ability.

The same thing applies to birth weight — two-thirds of the correlation between birth weight and later intelligence is explained by the mother’s own level of intelligence.

And again to breastfeeding.  When researchers looked at sets of twins where one twin was breast fed and the other wasn’t, there was basically no connection between breastfeeding and intelligence.  Of course, this is assuming non-breastfed babies are getting high-quality, sterile formula.

What About Dad?

Unfortunately, we don’t have much data on the paternal intelligence connection.  Partially this is because researchers haven’t collected as much data, and partially because it’s more difficult to be certain that a given guy is the biological father who contributed genetic material.

Live Long and Prosper

Another interesting connection in the data is that between early life intelligence and a longer life.  It’s more or less an upward-trending linear line: the smarter you are, the more likely you are to live a long life.  You’re both less  likely to die of external causes of death (murder, car accidents, etc.) and internal causes of death (cardiovascular disease, etc.).

Interestingly, there’s only one internal cause of death where the correlation does not apply, and that’s cancer.  There is one exception to this exception:  lung cancer.

PS:  It’s too late to be born to a smarter mom, but it’s not too late to make the most of what you were born with by signing up for our newsletter.

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  1. Ela says:

    Jesse–you know how much I love your show. Haven’t had a new one show up, so I’ve been catching up on a few I missed.
    This one was totally fascinating for several of the juxtapositions it brought, notably the application of statistics to offer insight into something normally thought of as more qualitative.
    A few things really jumped out at me, and I’d love your thoughts on them (if it isn’t too long after the event–still interesting, right?)
    (1) Maybe I missed it, but I don’t think “intelligence” was ever defined. So all these behaviors and outcomes were correlated with intelligence level, but what did that mean? Please understand, I’m not coming from the special snowflake “everyone is intelligent” position. On the other hand, the older I get the more varieties of intelligence I see, and the ways that these different intelligences are distributed within an individual could either improve or hamper their survivability (compare the mathematics savant who can’t decipher basic communication with the B-grade all-round student who would probably end up in a leadership position). So I’m wondering how intelligence was both qualified and quantified and triangulated for the different intelligences for this study.
    (2) I was puzzled that the longitudinal study didn’t seem to inquire into whether someone’s intelligence changed when they retested at 40 or 50. Some people definitely get smarter, whether through smart drugs or hard work or both, while others could get less smart through disease process or drugs, etc. I guess they were seeing how intelligence in youth correlated with those other things but still an interesting question.
    (3) Unrelated, but I thought it was fascinating that Dr Der suggested that 1st world breast milk alternatives would be advantageous partly because they are “sterile,” when we know (and you’ve had on the show) that it’s precisely the non-sterile nature of breast milk that’s considered part of its advantage in building the baby’s gut microflora.

    Okay–thanks for indulging my longwindedness–it’s a tribute to how much you get me thinking.
    (pronounced eela)

    1. Jesse Lawler says:

      Hi there Ela! (I haven’t re-listened to the interview/episode recently, so I’m going from memory here, but…) I think that the study was looking at standardized IQ scores, and didn’t subdivide that any further into “the Seven Intelligences” or the Emotional Intelligence spectrum, or anything like that. It seems like the consensus with IQ is that it’s an imperfect measure, but a) it’s definitely measuring something fairly stable and meaningful, and b) it’s the best single metric that we’ve got currently at representing what we think of in everyday speech as “intelligence,” even if it’s not the whole picture. As for #3 — Yeah, you’re right about that. I just read the book “I Contain Multitudes” by Ed Yong, all about microbial symbiosis and what a big deal it really is. I’m guessing that if Dr. Der were to read your comment and get a chance to re-state himself, he’d (probably) say that while a mother’s breast milk is optimal, infant formula made with comparatively sterile First World water is preferable to the same made with cholera-contaminated puddle water or something pulled from the Ganges River where people were doing their laundry in lye a little ways upstream. Or maybe he’s not hip to the newer research on just how much breast milk is a “microbial delivery system” from mother to child?

      And as for your long-windedness — no worries! Obviously I can’t throw stones while living in my own glass house of verbosity. 🙂

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