If you do this kind of research on a population where education has been less and less exclusive over the generations then surely you will find out that a score the correlates highly with education will correlate more among family members among your older population (where education was only available to richer families) then the younger (where education is accessible to the broader public).
This trend should persist as long as the quality of education remains unevenly distributed. You should also find very little to no heritability before or at the start of formal education (say age 10 and younger), and then heritability should increase as the discrepancies in the quality of education between families materialize.
To summarize this effect (called Wilson Effect) says nothing about how “genetic” IQ is, only that it correlates with the quality of education and that quality of education is not evenly distributed between families.
PS. As a manifestation on how insignificant this effect is in the scientific literature, Wilson Effect doesn’t even have a Wikipedia article, referring you to [the Heritability of IQ](https://en.wikipedia.org/wiki/Heritability_of_IQ) which references a paper about this effect only once in the beginning summary.
The researchers aren’t stupid, obviously they try to control for things like schooling.
Therefore, the strongest evidence for heritability of IQ (and the fact that it increases with age) comes from twin studies, where twins were separated at birth (by adoption).
As a fan of psychology, psychometrics are really frustrating. IMO they are given way too much weight in pop-science. There are a number of subfields within psychology that are doing amazing work, building out theories of behavior, cognition, etc. that builds well on top of each other, inspire theories in different sub-field etc. But psychometrics fit nowhere. Personality types and IQ does not explain behavior nearly to the same extent as simple environmental manipulation.
A couple of examples: People are likelier to cheat on a test if there is a visible cheater in the room regardless of how you score on a personality test. And you are on average quicker to spot a red square among red circles if you have been primed to spot a red square in a previous round, regardless of your IQ.
IMO the whole field of psychometrics is a scientific dead end. There are use cases for psychological testing (particularly in neuropsychology and as a diagnosis tool in psychiatry), but in general these tests are there to support a theory, not the whole basis for the theory.
> Some evidence suggests that heritability might increase to as much as 80% in later adulthood independent of dementia (Panizzon et al., 2014); other
results suggest a decline to about 60% after age 80 (Lee, Henry, Trollor, & Sachdev, 2010), but another study suggests no change in later life (McGue & Christensen, 2013).
Your source is actually just partially about the Wilson effect, it only spends a handful of paragraphs about it as it enumerates it among the “top 10 Findings From Behavioral Genetics”. The pivotal study is actually a meta-analysis —or rather a summary of studies—from 2013[1]. Read it if you want to be more convinced of this pseudo-science.
In the 10 years since the publication of this pivotal study, this Wilson effect has gone nowhere. Not even a wikipedia page to show for it.
> The researchers aren’t stupid, obviously they try to control for things like schooling.
Don’t be so sure. Twin studies on intelligence are reeked with bad science and malicious data manipulation. A lot of the researchers conducting these studies in the 70s and 80s were eugenicists doing scientific racism. Some even went so far as to forcefully separate twins into convenient families so they could be “studied” (See Peter B. Neubauer). The method of twin studies was actually proposed by non-other then Francis Galton (which should settle all discussion on the link to the eugenicist movement), and now century and a half later, we are still not convinced on the merits of this method.
Given this history, I don’t think it is smart to take any results from twin and adaption studies seriously. Some researchers don’t want to go that far, so if they actually look more broadly they conclude that these effects go away if you include people adopted into lower income families. James Flynn (of the Flynn-effect) actually argues for a Family effect on intelligence[2] as a result. But—as I say—I think Flynn is giving twin studies weight that shouldn’t be given, and would claim that results are inconclusive.
I actually want to go further and say not only that results are inconclusive, but they are irrelevant. Like I said, this is all pseudo-science. IQ is no different from SAT in that it is a metric whose only value is it’s score. It provides no insight into what we call intelligence, only some skills that people have acquired. Finding out how much better you can become at this skill by merits of your genes is a weird question that ultimately proves nothing.
This trend should persist as long as the quality of education remains unevenly distributed. You should also find very little to no heritability before or at the start of formal education (say age 10 and younger), and then heritability should increase as the discrepancies in the quality of education between families materialize.
To summarize this effect (called Wilson Effect) says nothing about how “genetic” IQ is, only that it correlates with the quality of education and that quality of education is not evenly distributed between families.
PS. As a manifestation on how insignificant this effect is in the scientific literature, Wilson Effect doesn’t even have a Wikipedia article, referring you to [the Heritability of IQ](https://en.wikipedia.org/wiki/Heritability_of_IQ) which references a paper about this effect only once in the beginning summary.