I'm not saying there is _no_ genetic component - I would be surprised if it wasn't. Just that compared to culture it's not important. I didn't read The Bell Curve, but as far as I know (and refreshed with a bit of googling) it states that IQ is partly hereditary - I don't think anybody doubts this - and makes it easy to go further and say some groups of people are smarter. This is most likely true, but still not so important.
I just finished reading What Intelligence Tests Miss, by Keith Stanovich. Summary: critical reasoning skills are much much better predictor of academic and social success then IQ, and (that's the shocker) largely _not_ correlated with IQ. And this is just one of the factors which influence success. Even if a group is a few IQ points above or below average, the final effect is very unlikely to affect anything.
edit: Oh, and yes, critical reasoning skills, even if they're not as well studied as IQ is (which is a shame, but it's being corrected) have a much much smaller genetic component and are easier to change during lifetime.
These books come out every so often. 5 years ago "emotional intelligence" sold copy.
IQ has a heritability coefficient of between .5 and .8. The rest seems to be non-shared environment. IQ is a very good predictor of academic success and future income (.7 to .8 correlation). There's a hell of a lot of research out there that has shown this again and again.
I'd like to see Stanovich's definition of "critical reasoning" and the studies that show it to be both uncorrelated with IQ and a good predictor of academic success and future income. There just isn't that much left to predict -- two uncorrelated variables can't both have a correlation coefficient of .8.
I'm going to bet that whatever he has defined as "critical reasoning" actually has a high correlation with IQ when measured.
But you won't find much more in this, unfortunately. For the link (or lack thereof) between IQ and critical reasoning search for Stanovich, it's mostly his own research. For link between (parts of) critical reasoning and academic success look up Mischel's marshmallow experiment. Personally I never saw 0.8 correlations with IQ mentioned anywhere, so I'd be grateful for a pointer.
I'm sorry about the number for income -- everyone has it at a correlation of .3 to .6. I believe that I was thinking of Lynn's numbers for national incomes, which is correlated at .7 or so to average IQ.
IQ is a very good predictor of academic success and future income (.7 to .8 correlation).
I'm joining the call of another participant here for references to back up that statement.
There just isn't that much left to predict
This seems to be mistaking a statement about what is currently observed with a statement about what might be possible under experimental interventions. No one has shown what the maximum possible influence of other independent variables might be.
I'm going to bet that whatever he [Keith Stanovich] has defined as "critical reasoning" actually has a high correlation with IQ when measured.
You will lose the bet. He and other authors on cognitive psychology and behavioral economics have already repeatedly replicated the result that many forms of rationality have meager or no correlation with IQ. He cites the references in his book.
Thanks for doing the math. I appreciate the pursuit of curiosity here on HN. There is a different issue here to be curious about, and that is exactly what a calculation of broad heritability definitely predicts. It predicts a lot less than what many readers unfamiliar with genetics might guess. It happens that some of the leading authors on human behavioral genetics just wrote an article about what heritability does and does not mean
Johnson, Wendy; Turkheimer, Eric; Gottesman, Irving I.; Bouchard Jr., Thomas (2009). Beyond Heritability: Twin Studies in Behavioral Research. Current Directions in Psychological Science, 18, 4, 217-220.
is now dead. But I have the full text of the article at hand, as I am currently attending a weekly journal club with some of the authors, and one key paragraph from the article must be read by anyone who draws conclusions from heritablity figures:
"Moreover, even highly heritable traits can be strongly manipulated by the environment, so heritability has little if anything to do with controllability. For example, height is on the order of 90% heritable, yet North and South Koreans, who come from the same genetic background, presently differ in average height by a full 6 inches (Pak, 2004; Schwekendiek, 2008)."
This simply reemphasizes a point that is familiar to anyone who has studied genetics carefully, namely that the pre-Mendelian concept of heritability says nothing about malleability, the degree to which a trait can be influenced by environmental variables.
Angoff, W. H. (1988). The nature-nurture debate, aptitudes, and group differences. American Psychologist, 43, 713-720.
Mange, A. & Mange, E. J. (1990). Genetics: Human Aspects.
Kaufman, Alan S. (1990). Assessing Adolescent and Adult Intelligence.
So the statement above that heritability somehow constrains the expression of IQ or of consequences of IQ such as occupational success is actually conceptually incorrect. But I appreciate you going to the effort of doing the math.
Another thought is that relating one correlation coefficient to another with linear algebra probably depends too heavily on applying linear tools to a not fully linear model. Increases of income are plainly linear and are on a ratio scale. (There is a zero point for income, and each dollar increase in income has the same magnitude anywhere along the scale.) But IQ test standard scores are at best ordinal scales, so it is already an abuse of mathematics to treat them as a linear variable, or to treat a figure derived from them as a linear variable.
IQ has a heritability coefficient of between .5 and .8.
Kindly explain why that is at all relevant to the issue at hand. (Since you have been carrying on a conversation with another participant here as the thread has deepened, it might be a good idea to make clear just what point of his you were responding to with that point.)
I can't say with certainty now, but when I was a genetics student in a fairly decent University, I remember we laughed at "The Bell Curve". It wasn't considered classic scientific reading.
There are a million places to start if you want to find a critique, but you can start with Gould's "The Mismeasure of Man".
"Mismeasure of Man" was propaganda written by a Communist paleontologist who knew next to nothing of psychometrics.
EDIT: Yes I'm a bit bitter about it, I read it and believed it for years, before learning better. I don't like wasting my time and I HATE being lied to (and even more being taken in).
There are a million critiques, many of which I've read. Some are better than others. By far the most ill-informed is The Mismeasure of Man. It's the worst of the bunch, written by an idiot. If you want a intelligent critique, I can point you to some.
Now, Murray had problems in The Bell Curve -- he didn't properly understand regression to the mean, for example. But did you students actually read it before laughing? He was pretty solid on most of the genetic topics he covered (a small part of the book).
