There’s recently been a lot of research on the genetic basis for academic accomplshments (i.e. grades, education level). One might ask why people are studying school grades when they could be studying IQ. Well, probably for the same reason that scientists have studied head size when they could have been studying brain size: The former is more accessible.
Just as it’s easier to put a tape measure around someone’s head than it is to remove their brain from their skull (or now days, shove them under an MRI), it’s easier to ask someone for their GPA or highest degree than it is to give them an IQ test.
As a result, HUGE sample sizes have been emerging linking genes to scholastic success (hat-tip to Steve Hsu):
FT.com: Genetic scoring predicts how children do at school
Professor Robert Plomin, senior author, called the study “a tipping point for predicting individuals’ educational strengths and weaknesses from their DNA”. It is published in the journal Molecular Psychiatry.
An individual’s “polygenic score” is based on the presence or absence of 20,000 common DNA variants across many different genes. Each has a tiny effect on its own but together they explain 10 per cent of the variation in children’s educational attainment at the age of 16.
Taking the square root of 10%, we learn there’s a 0.32 correlation between genetic grades and phenotypic grades (i.e. actual grades). That’s not a low correlation. What it suggests is that if you have an embryo that is +5 standard deviations in genetic grades, you can predict with 50% certainty that it will grow up to have grades that are at least +5 SD(0.32) = +1.6 SD (top 5% of an average class), and such an embryo would likely grow to get a graduate degree (top 5% in years of education which I assume would enjoy the same correlation) which is more than even I have! 🙂
Of course as commenter Mugabe/Videla would point out, we don’t know if these are independent genetic effects. That is, the 0.32 correlation between genetic grades and grades may only hold in specific cultures and thus needs to be tested internationally.
But is even a within culture 0.32 correlation a victory for HBD? It depends to what extent grades are caused by mental traits (as identified by psychology) as opposed to random factors. If grades are caused by mental traits then HBD predicts a high correlation between grades and genes because HBD believes mental traits are EXTREMELY genetic by (later) adulthood.
However if grades are caused by random factors (the school or teachers one has, etc), then even a moderate correlation between grades and genes is a win for HBD, because even with all those random factors, a genetic signal is breaking through the random noise.
My sense is that grades are caused in part by two putative mental traits: IQ (intelligence quotient) and CQ (conscientiousness quotient).
In the general, non-selected U.S. population, IQ correlates about 0.55 which academic success, whether you measure that success by grades in classes where the full range of ability exists, years of education, or prestige of college attended (if any).
Let’s say CQ also correlates 0.55 with academic success, and let’s say there’s a zero correlation between IQ and CQ. Then we might expect a composite measure of both traits (IQCQ) would explain 61% of the variation in grades
0.55(0.55) + 0.55(0.55) = 0.61
And yet genes only explain 10% of the variation in grades
If we assume that all 10% of the variation in grades that is genetic, is variation in IQCQ, it implies that 16% of IQCQ is genetic, does it not? (10/61 = 16)
That sounds pretty low considering mental traits are often claimed to have heritabilities approaching 80% (of course heritability is not precisely the same thing as phenotypic variation that is genetic, though the term is often used that way).
But maybe the study suffered from range restriction or maybe they only looked at a subset of genes, or maybe I’m making an error in my reasoning or assumptions.
Update July 31, 2016 (evening): On the other hand, finding genes that explain 16% of the variation in mental traits might be considered a HUGE victory for HBD, because we know from Genomewide Complex-Trait Analysis (GCTA), that the amount of variance explained by specific genes that are found for a particular trait are often AN ORDER OF MAGNITUDE less than the amount of genetic variation in said trait that is shown to exist (at least within countries)