Well, we know they are correlated. There might be a causal relationship as well, but the first study didn’t address that. In fact the entire premise of these studies seem to be to show the correlation and expect the reader to imply a causal relationship.
None of the studies I have read so far have considered the relationship between parental intelligence and parental income, and the hereditary relationship between parental intelligence and child intelligence. How much would that explain the income group differences (yes I know we disagree on the SAT as an intelligence test).
By the way, did anyone extend this study to consider the Asian students and their performance by income? I would expect a flatter curve there, which if true, could be illuminating.
The economy of the USA is set up that the most hereditary factor is wealth. So, if a parent has made a lot of money, their kid is going to inherit that money no matter how dumb or inept that kid is. Moreover, we have an economy in which money makes money, and all you need is to have a good financial adviser which your parents chose, and, if you inherited a few million dollars, you will stay rich your entire life, AND so will your kids.
The argument that rich people are smarter tends to be a circular one: How do we know that they’re smart? Because they made a lot of money. How do we know that making lots of money shows that they’re smart? Because smart people make lots of money.
Very wealthy people, especially those with inherited money, rarely demonstrate intelligence, except using indicators which can be increased through paying money.
How many super wealthy people have actually demonstrated innovative thought and creativity? Don’t tell me about Bill gates or other of these Dot Com millionaires, since almost all of them made their money through the sale of other people’s ideas. Almost none of them was selling an original idea of their own.
Moreover, having a single idea within you lifetime is not the sign of a genius. I have worked at half a dozen universities, and, to get a PhD, you have to have a major idea, but then, to get tenure, one must have at least three original ideas a year, AND be able to convince other people to put money down for those ideas.
Convincing people to buy a crappy overpriced product is nothing compared to convincing a grant agency to fund a research project. Yet these people, who are churning out original ideas at that rate, and getting them funded, would be considered less “intelligent” than some dolt who is getting $10 million a year from the billions of dollars that his father made, if we use wealth as an indicator of intelligence.
Finally, claiming that the wealth of a person indicates their intelligence is, essentially, claiming that the more one cares about anything else except money, the dumber a person is. If Einstein had REALLY been smart, he would have been a billionaire. The people who figured out how to send a person to the moon? A bunch of dummies, since none of them ever made more than a upper middle class salary, if that. The people who figured out how to make a flat screen with color? Must be pretty stupid, but the corporate CEOs who made lots of money off of that invention are the true geniuses. Jonas Salk may have created a vaccine for polio, but he couldn’t have been as smart as any of the thousands of millionaires in the USA.
Of course I’m being sarcastic, but I am simply demonstrating how ridiculous it is to use income as an indicator of “intelligence”.
As for how hereditary intelligence is? Nobody is all that sure. However, no matter how hereditary it is, it is always shaped by environment. Let us take, for an example, a trait that we all agree is extremely hereditary - height. Take the child of two basketball players, and raise them with limited access to good nutrition, and that kid will likely not even hit the average of our present society. They will likely bee one of the tallest kids among all the malnourished kids, but they would likely not be taller than middle class kids of average height.
The hereditary parts of intelligence would be no different. If the environment in which a kid grows up is not conducive to the development of their intelligence, they would likely demonstrate more intelligence than other kids who grew up in similar conditions, but they may also compare badly to average kids who grew up in conditions which were more conducive to developing intelligence.
We do not know, though, when it is set, since the brain is plastic, and human beings can be taught new things at least into the 70s.
It’s parental level of education that actually has a bigger say in SAT performance than income, of course they’re related, but kids with parents who both have graduate degrees do really well compared to those with only a high school diploma. I’m reading a book on inequality and one stat is that in 2010, 87% of the kids that scored above 700 on both sections had a parent with a college degree and 56% had a parent with a graduate degree. I’ll try to dig into the sources on that but it pretty much aligns with a lot of the posts here on the differences in achievement. One thing that I’m a little skeptical is the score differential, students in middle income do 135 pts better than the poor and 250 pts less than the rich, meaning a 375 pt difference between rich and poor, which seems large, unless it’s the old 2400 scale SAT.
In the extreme case of child neglect, lack of nutrition would be the dominant factor in height. It’s unfortunate too many of those cases don’t get reported to child protective services. That seems to be looking at the most extreme end of the spectrum. A lot of NBA greats were raised in low income urban areas. Then, there are eating disorders which lead to malnourishment, but cut across the full income spectrum.
@hebegebe my point is that, even simple traits that we understand pretty well, and which we know are very strongly heritable, have a huge environmental component. When we start talking about something as complex as human intelligence, to claim that it’s “all genetics” is ridiculous.
Though we are still have the barest of understanding of how brain function works and of the relationships between the genome and the brain, there are a few things that we do know.
We know that the rewires itself twice during childhood and adolescence, changes shape and function, and an adult brain is not merely a scaled up infant brain. It does not seem the least bit likely that the environment would have no effect on these processes and on the their outcomes.
If nothing else, PTSD, and the fact that trauma, which is about as environmental an factor as can be imagined, can affect brain structure, should tell us that a simple hereditary model of brain structure and function is invalid.
So if a short term trauma can cause parts of the brain to shrink, and to change the functioning of other parts of the brain, long after embryonic, infant and adolescent brain development are finished, how can anybody claim that the rest of the brain structure and function are even “mostly” determined by genes that one inherits from their parents, and are not affected by the environment in which one grows up?
In post #81 you tried to refute my point by using examples of extreme wealth, which is not the point I was making at all. Let me rephrase:
Intelligent people have more employment opportunities, some of which can provide considerable money. To be clear, I think it's commendable when a highly intelligent person decides to take a lower paying job they love, such as a schoolteacher or an academic. But many will choose higher paying positions such as medicine, finance, software engineering, etc. As a result, income skews higher with intelligence. This correlation is fairly low (estimates I have seen are around 0.3), but it's clearly there.
Intelligence is significantly heritable, similar to how height, good looks, or athletic talent is heritable. This makes some people uncomfortable, but it's reality. And I grant that environment affects how well these genetic capabilities become realized. A person with the genes to become tall can have stunted growth due to poor nutrition. Likewise a person with the genes to become intelligent can suffer in a home that doesn't provide mental stimulation. This requires a certain baseline level of income and parental involvement, but beyond that there are only marginal effects .
Given the two effects above, you are very likely to end up with a scenario that shows that test scores correlate to parental income. In fact, I would be hard pressed to come up with general scenarios where this is not true (corner cases are easy enough to find however). But note the causal relationship is not the parental income, but the intelligence that is tied to both.
And this approach shows it even more clearly. If you plotted a child’s test scores vs a parent’s educational attainment, you would see rising scores as parental educational attainment increases.
And of course, parental degree is correlated with income (except perhaps for PhDs in academia). So again it appears that parental income is correlated with a child’s test scores without it being the causal link.