Physicist Steve Hsu recounts IQ heritability figures from a 2010 metanalysis of twin and adoption studies:
He goes on:
But now that we have inexpensive genotyping, we can study heritability of a quantitative trait by looking at unrelated (or only distantly related) individuals, and asking to what extent similarity in genotype is correlated with similarity in phenotype. A simple way to think about this is to imagine that we have a sample of N people for whom both phenotype (measured g score) and genotype (e.g., SNP profile) are known. Form all possible pairs and plot magnitude of difference in g score against genetic distance between the individuals in the pair. The g score difference should (on average) decrease as the genetic distance goes to zero (at which point the pair are MZ twins; but we avoid the confound of shared prenatal environment). Even if we have no identical twins in the sample, and even if none of the people in the sample are closely related to each other, we can extrapolate to zero genetic distance to obtain an estimate of heritability. An analysis along these lines (more technically, a global fit across all SNPs of total heritability) for height yields a result which is consistent with the narrow sense heritability estimate from twin and adoption studies. The results for g have not yet been published, but rumor has it that they also support earlier estimates such as those given above.
Hsu points out that one way to look into the Flynn Effect would be to find elderly people whose IQs were measured for military enlistment / conscription purposes in the middle of the 20th Century.
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10 comments:
You will find few comments here because this is not material for griping.
Any ideas why the anomaly in the UK correlation?
Gilbert P.
Just checking: MZ is for identical twins and DZ for fraternal?
Any ideas why the anomaly in the UK correlation?
Gilbert P.
I don't think there's an anomaly. Heritability increases with age, while the effects of shared environment wane with age. The mean age in the UK sample is 11.57 years (range=10.08–13.74), which is lower than in the other samples, except for the Ohio one. The Ohio sample has a mean age of 6.07 years (range = 4.33–7.92), which means that the shared environmental effects are still strong.
Falconer's formula gives the following broad-sense heritabilities for the samples (mean ages and age ranges in parentheses):
Ohio: 42% (mean=6.07; range=4.33–7.92)
UK: 48% (mean=11.57; range=10.08–13.74)
Minnesota: 52% (mean=13; range=11–17)
Colorado: 58% (mean=13.12; range=6–25)
Australia: 70% (mean=16.00; range=15–22)
Netherlands: 50% (mean=17.99; range=5.67–71.03)
The paper in question can be read here; it is precisely about the linear increase of the heritability of IQ with age.
The results for g have not yet been published, but rumor has it that they also support earlier estimates such as those given above.
Anti-hereditarians have fought a rearguard action against hereditarianism for many decades. Each new study has made their blank slatism more and more absurd. All they really have left now are some feeble technical criticisms of the twin method, but if and when heritability studies that do not depend on twins produce results similar to twin studies, they'll have nothing.
"Any ideas why the anomaly in the UK correlation?"
Drink?
The great search for the IQ gene will be as fruitless as the great search for disease genes. IQ is indeed heritable but there will be no simple genetic pattern to reveal just how it is inherited:
http://independentsciencenews.org/health/the-great-dna-data-deficit/
Yes.
MZ = monozygotic (identical)
DZ = dizygotic (fraternal)
"All they really have left now are some feeble technical criticisms of the twin method, but if and when heritability studies that do not depend on twins produce results similar to twin studies, they'll have nothing."
That is one of the reasons this new technique is important. I doubt the blank slaters will understand it well enough to mount much of a response. They'll just ignore it as long as they can.
@Dutch Boy: I suggest you read the Visscher paper on "missing heritability" and height. It is linked to from the original Hsu post.
TH, thanks, very interesting.
G.P.
Dearieme, Ha! But even chavs don't pile into the lager at age 11, do they?
G.P.
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