At first glance, it might sound strange to suggest that an IQ test given at age seven is more accurate than IQ test taken when you’re an adult and your brain is fully developed. Indeed one of the most stunning discoveries of behavioral genetics is the doubling (yes doubling) of IQ’s heritability from childhood to older adulthood. Of course the majority of these studies estimate heritability by comparing the correlation of MZ twins raised together with DZ twins raised together; a method that is vulnerable to criticism because of the equal environment assumption. But we have corroborating evidence (i.e. the zero correlation between the IQs of unrelated people raised together, the vanishing of IQ gains caused by adoption) that IQ does indeed become more genetic with age, at least within a given developed country.
But the rising heritability of IQ might be misleading. We know from the Flynn effect that shared environment effects like schooling and socioeconomic status have HUGE effects on IQ (though perhaps not intelligence) but as scholars Dickens and Flynn brilliantly noted, within generations, these cultural effects get counted as genetic effects because people with certain genes spend more time in culturally stimulating environments.
So when we say IQ is 80% genetic by late adulthood, we’re not necessarily saying genes DIRECTLY cause IQ. Rather genes cause you to engage in IQ increasing behavior. It’s a bit like saying weight is highly genetic, when what we really mean is diet and exercise choices are genetic (which cause weight). So adult IQ is not necessarily measuring who is the most biologically clever. It could merely be measuring who got a PhD in English literature, thus artificially boosting their score on vocabulary beyond what it should have been.
In order to truly measure REAL intelligence (if you believe in such a construct), you need to return to childhood, where people haven’t had as much time to coach themselves for IQ type tests. Of course children who come from rich and educated homes have an unfair advantage on IQ tests but because the gene-environment covariance is much smaller in kids than in adults, the effects of shared environment can be separated from the effects of genes by statistically adjusting for social class.
How do you adjust childhood IQ for social class? Let’s say you have a seven year-old child from an upper class family who scores 120 on an IQ test (white norms) This implies he’s smarter than 90% of white Americans his age. However most white kids his age were not raised in upper class homes. Now you could compared him only to other white kids from his class, but that’s misleading because they’re a genetically elite sample (since they inherited not only their social class from their parents, but the genes that caused it). What you need to do is compare him to a genetically random sample of white kids raised in upper class homes, and the closest we have to that are adoption studies.
After correcting for old norms and converting to white norms, the sixteen white adopted kids in the Minnesota transracial adoption study had an age seven IQ of 109 with an SD of 11.3, compared to the general U.S. white population which by definition has a mean IQ of 100 with an SD of 15. What this shows is that if every white seven year-old in America was raised by the upper-class, the mean IQ would rise and the variability would shrink. This makes sense because we’ve removed a huge chunk of the variance from IQ (cultural effects) leaving hopefully only direct biological effects (genes and biological environment).
So a white upper class seven-year old with an IQ of 120 is 0.97 SD above the mean if all white kids were raised in his social class. Thus his social class adjusted IQ would be 115.
If being raised in an upper class home causes the mean IQ to increase by 9 points (and the SD to drop to 11.3) we might guess that being raised in a lower class home causes the mean IQ to drop by 9 points. So if all white kids were raised by low income high school dropouts, the IQ distribution at age seven might be 91 (SD 11.3).
So a seven-year-old from a low class family with an IQ of 120 is an astonishing 2.57 SD above the mean if all white kids were raised in such homes. His social class adjusted IQ would be an incredible 138!
So here we see two kids with an identical IQ score, but by adjusting for social class, we find that one kid is actually 23 IQ points smarter than the other. The kid from the lower class will probably get a good education and enter the upper class when he’s older, and by 40, his measured IQ might become as high as his age seven adjusted IQ. By contrast the upper class kid might go down a bit in social class, causing his measured IQ at age 40 to also match his adjusted IQ at age seven.
On the other hand, if the upper class kid is especially curious, and the lower class kid has no interest in learning, the opposite might occur. This is why IQ tests when measured in childhood, if properly adjusted, might be far better measures of real intelligence than measurements taken after kids are old enough to shape their own environments in ways we can’t adjust for.
Pumpkin Person 
“It’s a bit like saying weight is highly genetic, when what we really mean is diet and exercise choices are genetic (which cause weight).”
Ready to have your mind blown pp?
https://intensivedietarymanagement.com/first-law-thermodynamics-irrelevant/
https://intensivedietarymanagement.com/insulin-causes-weight-gain-hormonal-obesity-iv/
In first world countries the heritability of BMI is around .8, same heritability as height and IQ. Some researchers argue that the increase in average height coincides with the increase in weight. Basically, as countries become first world, they get fatter as they are able to reach their genetic height but that same abundance of food makes people fst leading to the high heritability of BMI in first world countries.
On the subject of IQ, I get what you’re saying. But when genetics takes hold at adulthood matters more than when intelligence is malleable and molded by environment. IQs when tested at adulthood tell the real story.
Remember that ”western environment” is a anomaly, and not the rule.
Which is why I said first world countries Santo.
ok.
Iq don’t become more genetic with age, become more stabilized.
stabilized IS NOT EXACTLY the same than genetic, period.
Heritability is lower in childhood which is why with an enriching environment IQ can be raised but genetics takes effect at adulthood making environment meaningless.
RR- really? Linda G has said just the opposite. I’ll try to find the interview where she says it. Do you have a source?
Arthur Jensen says it in one of his books, I forget which. Is the Gottfredson interview the one with Molyneux?
And it’s also inferred from the heritability of IQ at childhood all the way to adulthood. With lower heritability, enriching environments can raise IQ, but at adulthood the genes take effect and environment becomes meaningless.
Let me check Rushton and Jensen 2005, I think Jensen says something along those lines.
yes, it was with Molyneux. He’s a retarded, typically (“If you can’t explain something simply, you don’t understand it well enough”, especially if it’s Childrens’ movies), but this interview was interesting.
*retard*
”heritability is lower during childhood”
what*
” is a statistic used in breeding and genetics works that estimates how much variation in a phenotypic trait in a population is due to genetic variation among individuals in that population”
Heritability only ‘there’ before the birth*
You guys are confusing heritability with genotypicability?? Intrinsic direct causation??
”my iq scores reflect purfeclty my cognitive mood”
”my iq scores was affected by my affective mood”
Yup son
Verbal cognition is pretty important
Like it or not
“people who have vulgarly superficial knowledge about ‘intelligence’ … studying intelligence” = hbd
Mister Pritchard syndrome*
The genetic charge of the genotypical intelligence is the same in all ages, period.
Citation needed.
It’s not the same. It hits 80 percent at adulthood, 40 percent at age 7 and 20 percent at age 5.
You just memorize it.
”genetic is not = stabilized…”
interpret this sentence, please.
If the environment really can alter ”for the last of our days” part of us so seems logical verify the pure/genotypical intelligence when it have zero-environmental influences, fresh out of womb.
And genotypical ”intelligence” ”or” cognition need to be analysed without affective influences, neutralizing the mood states during the performance.
I enjoyed reading this. I come from an underclass white American family (raised on welfare; no father; mother is an 8th grade drop out) and frequently wonder how it affected my adult IQ. My childhood IQ was 139 and while I’ve never had it measured as an adult, I suspect my adult IQ must be several points lower since I didn’t pass through a tract of life that would likely correspond with a high IQ (i.e., getting a PhD in English, to use your example).
On a related note, I only had my IQ tested as a child because my kindergarten teacher assumed I was mentally retarded and wanted me moved into a special education classroom. I wonder how many of my fellow high IQ PP readers were mistaken for autistic as children? Probably quite a few, if I understand J.P. Rushton’s genetic similarity theory.
“I wonder how many of my fellow high IQ PP readers were mistaken for autistic as children? Probably quite a few, if I understand J.P. Rushton’s genetic similarity theory.”
Care to explain, please? Do you think that your kindergarten teacher sensed your lower class genes and tried to kick you out of the nest? But such teachers aren’t exactly academics, are they?
Do you think that your kindergarten teacher sensed your lower class genes and tried to kick you out of the nest?
No, although that is actually an interesting theory, come to think of it. I simply meant that I’ve known several other high IQ people who were mistaken at some point for autistic (and some who are actually high functioning autistics). I’m curious if I’m the only reader of this blog who was mistaken by a childhood educator for a mental retard and forced to take an IQ test to determine the extent of their retardation. If I never had this experience, it is possible I would have never known I was gifted.
An IQ of 139 is obscenely high for a lower class kid.
so if the correlation between IQ and income is 0.4, a kid with that IQ would be expected to have income as an IQ equivalent (as an adult?) of (39×0.4)+100= 115,6, or +1SD from the average person’s income?
Correct, assuming your income Z score is normalized
Are these changes between environs true for performance scores? Block design..? Or is it mostly verbal IQ?
Are these changes between environs true for performance scores? Block design..? Or is it mostly verbal IQ?
Excellent question. I don’t know, but the answer to your question would have great theoretical implications.
I’ve been reading these past 2 days that reading has real increases I’m verbal IQ.
Thoughts PP? I’ll link studies in a bit.
Charles Murray delight us with your wisdom recently
”Verbal iq is boring”
this is a implicit contradiction because if verbal iq is so boring, marginal, without importance, why sir Murray can write a semantically coerent sentence**
because rightists can see the naked body of the king (while leftists tend to see the non-existent ”new clothe”) they tend to think they are jeeniiias… this is just the obvious to do.
I dont think you can infer too much from childhood. As yoi say yourself, the brain is an organ not a deus ex machina.
The organ grows with electrical stimulation, pain, hormones , diet, cardio exercise and so on. Child iqs are going to be all over the place before settling into long term equilibrium as the smart pick the right lifestyles.
Therez too much randomness going on in childhood to say definiteively such and such would be a good physicist or doctor etc.