A popular formula for estimating heritability (H^2) is as follows:
H^2 = 2[(correlation between MZ twins raised together) – (correlation between DZ twins raised together)]
Some have criticized the formula for assuming that MZ twins and DZ twins raised together have the same environment, but some of this criticism has been dismissed by blogger “Wax Empirical” who writes:
The vast majority of this research finds little to no evidence that twin studies are biased in this regard. Most twin studies have cited this research in support of what is known as the equal environment assumption or EEA for short. The equal environment assumption is perhaps a misnomer because it doesn’t mean that we assume that MZ twins share environments that are as similar as DZ twins. Instead, the equal environments assumption simply states that environmental similarity between twins does not have much of an impact on trait similarity.
One major way that MZ twins raised together differ from DZ twins raised together is that the former generally share the same placenta and the latter virtually always grew in different placentas. So even if one agrees that raised together twins of both types share the same cultural environment, the prenatal environments are clearly different.
As commenter Jorge Videla has mentioned, more sophisticated research done in Canada and France has studied identical twins grown in different placentas. I will focus on the Canadian research by Rose, Uchida, and Christian (1981) since it is based on adults, which is the age when heritability is maximized. A sample of 15 pairs of two placenta MZ twins and 28 DZ twins (all aged 20-44) were tested on Vocabulary (the most g loaded measure of Verbal IQ) and Block Design (the most g loaded measure of true Spatial IQ); all pairs presumably raised together.
The results showed that for Vocabulary, the two placenta MZ twin pairs correlated an astonishing 0.95, while the DZ twins correlated 0.55. Applying the formula cited at the start of this post, a heritability of 0.8 is obtained.
By contrast for Block Design, the two placenta MZ twin pairs correlated 0.48 and the fraternal twins correlated 0.44. Applying the same formula, a heritability of 0.08 is obtained.
I don’t know if the composite score of both subtests combined was obtained, but I guess we can crudely average the two heritabilies and guess that Full-scale IQ might have clocked in with a herirtability of only 0.44.
So maybe us Jensenists were wrong to think IQ has a sky high heritability of 0.8 in adults; only verbal IQ has such high heritability. But the sample size of this study is not huge, and the IQ test given was abbreviated (only two subtests) so only tentative conclusions are warranted.
But one thing HBD deniers are incapable of understanding is that relatively culture fair tests really do exist. HBD deniers make the mistake of thinking that because culture reduced tests are not strong measures of genes, they must be measuring culture. But what this placenta research shows is that it’s not differences in cultural environment that are driving down the heritability of culture “fair” tests like Block Design, but rather differences in prenatal environment. In other words, culture reduced tests really are measuring biological intelligence, not acquired cultural skills as critics claim, but biological IQ != genetic IQ.
This is why I have always favored Richard Lynn’s brilliant nutrition theory as the single biggest explanation for the Flynn effect. As Lynn brilliantly noted, it is the culture reduced tests of spatial reasoning that show the biggest Flynn effect and these just happen to be the same subtests that are more impaired by prenatal malnutrition. By contrast, the culture loaded measures of verbal knowledge show smaller Flynn effects, and seem unscathed by prenatal malnutrition.
But for decades, most experts in the field have ignored Lynn’s great insights and instead violated Occam’s razor by looking for cultural explanations for why culture reduced tests were showing large Flynn effects! Is that dumb or what?
To be sure, some culture reduced tests that require a lot of persistence and concentration (i.e. matrix reasoning) probably can be strongly influenced by cultural attitudes, but fun culture reduced tests involving playing with blocks and wooden puzzles, really are culture fair (assuming everyone understands the instructions and has basic motivation) in all but the most extreme of cases. But that doesn’t mean they’re necessarily heritable!
Now some folks might be getting excited at the possibility that adult IQ has a heritability of only 0.44 because it implies all the races are equally intelligent, right? Wrong! Races that have been separated for tens of thousands of years have had plenty of time to evolve significant genetic differences in IQ, even with such a low heritability. Instead a low heritability makes it even harder to close the genetic gap between races, because even generations of selective breeding will not bring low IQ races up to the level of high IQ races.
Sadly, it also means low IQ white trash might be able to feel genetically more intelligent than high IQ Ivy League minorities, because the IQ differences between them are environmental, while the racial differences between them might reflect genetic ability.
PP,
explain me how twins study can be conceptually correct with heritability (or heredity)**
Tell me how heritability studies should be- done* By intergenerational genetic transmission or by monozygotic twins*
Don’t seems obvious that quasi-clons should- be very similar genetic heritage**
High heritability just means that if we all had clones, born in random wombs, raised in random homes, the highest IQ people would also usually have the highest IQ clones.
It doesn’t mean you necessarily inherited your IQ from your parents. A genius can give birth to a Downs Syndrome child.
PP,
heritability is/are a phenotypical probabilities, then the fact that genius may had a down syndrome baby don’t mean nothing,just high mutational load of genius, specially the creative.
I have by now slight perception that you don’t understand what you wrote.
And you don’t answer my question.
Your comment don’t make any sense, sorry, i don’t understand.
then the fact that genius may had a down syndrome baby don’t mean nothing,just high mutational load of genius, specially the creative.
But a lot of people think heritable means you inherited it from a parent, so I was trying to clarify in case you were confused about that: heritable just means the genotype correlates with the phenotype. Indeed broad heritability is literally that correlation squared.
I have by now slight perception that you don’t understand what you wrote.
And you don’t answer my question.
Perhaps I didn’t understand the question
”But a lot of people think heritable means you inherited it from a parent, so I was trying to clarify in case you were confused about that: heritable just means the genotype correlates with the phenotype. Indeed broad heritability is literally that correlation squared.”
Nope,
they are right, common sense about it is right.
PP,
we are talking about selective pressures. It mean intergenerational genetic transmission, natural or any other kind of selection.
Look obvious that monozygotic twins will shared very similar genetic heritage.
Phenotype= genetic or expression or exteriorization of genes.
Re-read my second comment and tell me what the word ”PROBABILITY” on this context mean, please.
By contrast for Block Design, the two placenta MZ twin pairs correlated 0.48 and the fraternal twins correlated 0.44. Applying the same formula, a heritability of 0.08 is obtained.
Sounds like bullshit.
But I agree, high heritability of IQ is preferable to low heritability.
Sounds like bullshit.
Maybe. But at least the study considered prenatal factors which many heritability studies don’t seem to fully consider.
But I agree, high heritability of IQ is preferable to low heritability.
LOL! Sounds like you were desperate to find something something positive to say about the post, and there’s just nothing positive to say. 🙂
I just said that because I’ve never seen any study make an estimate for IQ subtest heritability that’s so low. I’m willing to bet heritability goes up substantially for Block Design as people reach aduthood.
I’ve seen several studies on fetal alchol syndrome that showed initial deficits in intellectual functioning in children that couldn’t be predicted from their parents IQ, but improvements in said functioning as they got older to levels that one would expect (which still wasn’t that high, because anyone with a mom who would drink during pregnancy is probably getting dumb genes).
Environmental arguments for IQ really do suck for me, because it means we have no idea how to improve IQs for lower intelligence races, but if it’s highly heritable, then we know what we need to do: institute a selective breeding program.
And off topic: you should do an IQ estimate for attendees at Dragon-Con. I passed through yesterday and all the guys (and girls) look really dorky, so they must be smart.
I just said that because I’ve never seen any study make an estimate for IQ subtest heritability that’s so low. I’m willing to bet heritability goes up substantially for Block Design as people reach aduthood.
The data I cited was from adults. I’ve never seen an IQ study give such a low adult heritability either, but then I’ve also never seen a study that gave this much attention to prenatal environment It could still be very wrong though, since it’s just one small unreplicated study
Environmental arguments for IQ really do suck for me, because it means we have no idea how to improve IQs for lower intelligence races, but if it’s highly heritable, then we know what we need to do: institute a selective breeding program.
Is that seriously the reason you prefer high heritability or did you just think of that because of the end of my post? If that is the reason you prefer high heritability, it’s ironic, because most people who want to help minorities prefer low heritability because they think it makes IQ more malleable.
And off topic: you should do an IQ estimate for attendees at Dragon-Con. I passed through yesterday and all the guys (and girls) look really dorky, so they must be smart.
LOL! Very true.
Is that seriously the reason you prefer high heritability or did you just think of that because of the end of my post? If that is the reason you prefer high heritability, it’s ironic, because most people who want to help minorities prefer low heritability because they think it makes IQ more malleable
I got that from an argument Razib Khan made several years ago on “Gene Expression”. But I also just think it’s unlikely that the gap between the poor and the rich, regardless of race, is predominantly environmental (within societies).
Sounds like bullshit.
Sounds like you wish it is bullshit because you are Black and you want the best for you your race 🙂
And btw Pumpkin, does it confirm my theory on verbal IQ developing after spatial IQ and so, being less sensible to prenatal environment ?
And btw Pumpkin, does it confirm my theory on verbal IQ developing after spatial IQ and so, being less sensible to prenatal environment ?
I suppose. There’s a theory that human growth from infancy to adulthood mirrors our ancestral past, so whatever came first in evolution, should also come first in babies.
It does sound like bullshit, even Steve Hsu said that study designs which try to include prenatal factors are crap since controlling for those things aren’t possible, and even then there’s a genetic confound, which JayMan pointed out.
In any case, the HBD deniers there are very much incorrect if they think that these studies mean anything.
And if IQ heritability is low it mean that if the SD of the White race is 15 , the SD of the gentic of Whites would be much lower ?
(I am writing while walking)
Of the gentic IQ of Whites*
No, because the IQ by definition has a standard deviation of 15 (in whites). That is, however your measuring it, you convert the white standard deviation to 15 and convert the white average to 100, for it to be called a (genetic) IQ.
However using an IQ test, which measures phenotypic IQ, not genetic IQ, a low heritability would means that if every white could be given the same environment, the average white IQ might go up to say 105 and the standard deviation might go down to say 10. But if that happened, they would just adjust the tests so that 105 = 100 and 10 = 15.
And then phenotypic IQ would equal genetic IQ, because you removed the environmental variance, but maintained the same scale (mean = 100, SD = 15)
Of course all this assumes the G = P + E model which Mugabe/Videla hates.
How do genes affect cognitive ability or other human quantitative traits such
as height or disease risk?
Lynn has also wisely pointed out that the Flynn effect cannot be the result of more or better schooling, because the effect already shows up on simple tests given to wee infants, long before those infants start attending anything that could be considered formal schooling.
The Flynn effect gains on infant motor tests and adult spatial tests are probably related to prenatal nutrition, not schooling, but the gains on verbal test are probably caused by schooling.
This is still a little confusing.
“biological IQ != genetic IQ”
If I had a clone my IQ would be about 0.95 the same as His.
And my parents would have an IQ about 0.45 the same as my IQ.
Biologically the way my brain uses energy(genes for energy) would max out because of good nutrition giving a max potential for IQ.
good genes + good food should = eficient metabolism.
“culture reduced tests really are measuring biological intelligence, not acquired cultural skills as critics claim”
Your wording may be obfuscated.
What is the distinction?
I remember you said before it has something to do with crystallized(cultural) and fluid heritability?
what is genetic IQ?
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