There were 80 kids in my home school group that were in my grade, maybe half skipped a year when they went to school. That's a small sample size, but not that surprising as most home school parents highly value education.
“the most recent studies showing heritability for IQ as high as 80%.”
Whether it's relevant for the main topic... that's an interesting question. Very much so. But I don't dare speculate, and I don't have data.
https://areomagazine.com/2020/09/02/the-nature-behind-human-...
Skills, accurate self-image, and cultural competence. etc, are of course a different matter.
Maybe he’s talking about these things, but they aren’t the same as intelligence.
And the article says: "on average, psychological traits are extremely heritable, at around 50 per cent." It's hard to argue for a definition of "intelligence" that wouldn't be a psychological trait.
What if you’ve heard definitions for intelligence that aren’t measured by IQ test scores and then someone uses IQ test scores to argue for the heritability of intelligence?
> And the article says: "on average, psychological traits are extremely heritable, at around 50 per cent." It's hard to argue for a definition of "intelligence" that wouldn't be a psychological trait.
Its equally hard to argue for an average of things which are not faithfully represented by numbers.
> Its equally hard to argue for an average of things which are not faithfully represented by numbers.
How do you represent, say, extroversion with numbers? It's messy and any particular measure is probably not a good one, but what people do is come up with a list of questions like "Statement: I am excited when I go to a social event full of strangers; rate your agreement from 0 (Strongly Disagree) to 4 (Strongly Agree)", and add up the numbers to create a score. It's kind of arbitrary and has a lot of "noise" in it, but on the other hand there is enough signal that it is measuring something real. If you need to turn it into a binary classification, you choose a cutoff number, which will again be semi-arbitrary and make errors, but again can be good enough to draw useful conclusions. You can then apply that measure to, say, biological siblings who were both adopted, or (best) to identical twins separated at birth vs fraternal twins separated at birth, and see if genetic similarity correlates with similarity of your measure. From that kind of data, you can get a vague idea of heritability.
If the thing you're discussing isn't measured by existing tests, fine. If the thing you're discussing has a logical definition and is important, but you think there can be no tests to produce even a vague measure, then I would guess you just haven't tried very hard.
Its hard to measure a correlation between a set of numbers and a set of NaN’s. However the prior here is that 50% of psychological traits are not heritable, so our prior is that we have approximately equal chances of a trait being heritable or not. What is likely is that some aspects of intelligence are heritable and some are not, and if the statistics that indicate heritability are measuring anything, they are measuring that part of intelligence that is measured by tests AND is heritable. Which is obviously poor evidence for those being the only relevant aspects of intelligence.
> It's kind of arbitrary and has a lot of "noise" in it, but on the other hand there is enough signal that it is measuring something real.
The “something real” is “how people respond to tests”, the assertion that “how people respond to tests” is positively correlated with “extraversion” is a claim that needs evidence. Mere assertion is not sufficient.
> If you need to turn it into a binary classification, you choose a cutoff number, which will again be semi-arbitrary and make errors, but again can be good enough to draw useful conclusions.
The results of a research program are more often useful to the person who is credited with conducting the research than they are useful to the person who is concerned with making accurate predictions of the real world phenomena allegedly represented by tests.
> You can then apply that measure to, say, biological siblings who were both adopted, or (best) to identical twins separated at birth vs fraternal twins separated at birth, and see if genetic similarity correlates with similarity of your measure. From that kind of data, you can get a vague idea of heritability.
Yes, you can get a good idea of the heritability of how a person responds to tests. However the program you described does nothing to validate the responses on tests to any real-world phenomena.
> If the thing you're discussing isn't measured by existing tests, fine. If the thing you're discussing has a logical definition and is important, but you think there can be no tests to produce even a vague measure, then I would guess you just haven't tried very hard.
Perhaps one has tried hard enough to realize that the problem is less tractable than you suppose. One could also observe that “intelligence” is socially constructed and does not in fact have a logical definition that is based solely on objective factors.
This isn’t true. Every psychological trait has a large heritable component. The lowest value I’ve ever seen for heritability of intelligence is on the order of 0.6 and 0.8 is just as common.
> Genetic Influence on Human Psychological Traits
> There is now a large body of evidence that supports the conclusion that individual differences in most, if not all, reliably measured psychological traits, normal and abnormal, are substantively influenced by genetic factors. This fact has important implications for research and theory building in psychology, as evidence of genetic influence unleashes a cascade of questions regarding the sources of variance in such traits. A brief list of those questions is provided, and representative findings regarding genetic and environmental influences are presented for the domains of personality, intelligence, psycho- logical interests, psychiatric illnesses, and social attitudes. These findings are consistent with those reported for the traits of other species and for many human physical traits, suggesting that they may represent a general biological phenomenon.
...
> own positive correlation between tests of mental ability, the evidentiary base for the general intelligence factor. This value is typically about .30. The genetic correlation be- tween such tests is, however, much higher, typically closer to .80.
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.397...
> Heritability is a technical measure of how much of the variance in a quantitative trait (such as IQ) is associated with genetic differences, in a population with a certain distribution of genotypes and environments. Under some very strong simplifying assumptions, quantitative geneticists use it to calculate the changes to be expected from artificial or natural selection in a statistically steady environment. It says nothing about how much the over-all level of the trait is under genetic control, and it says nothing about how much the trait can change under environmental interventions.
[0] https://plato.stanford.edu/entries/heredity/#PhilIssuArisTwi...
Whatever his definition is, what we mean in this conversation is that smart parents tend to have smart children, and dumb parents tend to have dumb children, and that there's little one can do with the environment (besides minimum nutrition) to change that.
Right above my comment is another linking the wikipedia page on IQ heritability. That would be a good example of a source. Meta-studies are a good option. Longitudinal studies are a decent one. Single studies are usually useless, but they're at least a good starting point for a productive conversations.
Until then, whether this is really useful or not, I want to mention that time and again my experience in academia is that topics like these where we really depend on the judgement of the investigators a lot need to be carefully evaluated. Academics have a tendency to over exaggerate significant beliefs from highly questionable data points from very few studies. I'll revert back after going through the literature best I can.
You're right in that there is a limited number of studies, in part because you're looking at small populations and you don't get that many new adoption or twin cases each year. However, in that regard it's worth looking at equivalent studies worldwide who each have tested their local adopted or twin children; as far as I understand, these studies in different countries generally confirm the same or similar results, but I have not personally gone in detail to verify that.