So the kids in the study were selected because their parents were poor, and the average IQ of the kids in the study was around 80. That certainly signals a correlation, and since these are kids and don't have agency over their economic situation, it suggests a direction of causation too.
Logically money should have no direct affect on intellectual capacity (e.g. see my other argument about taking the money away and giving it to someone else).
In this case, I think the causation is in the other direction. Over time, people with less intellectual capacity will be less successful, and therefore poorer. That is rational. The other direction is irrational.
> Logically money should have no direct affect on intellectual capacity
If intellectual capacity was purely genetic, this would make some sense. You can't buy better genes for yourself or your children. [1] However, intellectual capacity is demonstrably affected by a variety of environmental factors, including early nutrition, that themselves are strongly influenced by wealth, so we've got pretty good ideas of some of the mechanisms by which wealth influences intellectual capacity.
> In this case, I think the causation is in the other direction. Over time, people with less intellectual capacity will be less successful, and therefore poorer. That is rational. The other direction is irrational.
I think you are confusing "rationality" with fit to your preferred, non-evidence-based, model of the way the world should work.
[1] Well, except that wealth affects mate selection opportunities, so, even with purely genetic intellectual capacity, wealth could plausibly have some influence.
Where do you pull "40 point IQ difference" from? The gap between these impoverished kids and normal is only 20 points. And that is easily explainable with nutrition, stimulation, and education.
Independently, the estimated difference between average IQ in the mid-30s and today is 20 points. See http://en.wikipedia.org/wiki/Flynn_effect for verification. In that time period the main things that have changed are nutrition, stimulation and education.
So there you have it. Two unrelated analyses of completely different things finding that nutrition, stimulation and education can explain 20 point IQ differences between otherwise similar populations.
It depends on how you ascribe causation to hereditary factors. Does it make sense to say that a 4 year old is poor because of his low IQ? I don't think so, because a 4 year old has no agency over his economic circumstances.
Does it make sense to say that a 4 year old is poor because of his low IQ?
No.
But it does make sense to say that a 4 year old is both poor and has a low IQ because his parents do. And this applies whether you believe that his low IQ is due to heredity or a poor environment caused by his parents.
I actually don't believe at a micro-level that causation comes into play at all. I was responding to the statement that at a macro-level there is probability of causation, and it is more rational that poverty is caused by stupidity than poverty causes stupidity. The latter is nonsense.
Part of the IQ test includes vocabulary, and it's not that much of a leap to say that more highly-educated people have a broader, deeper vocabulary, even when controlled for cultural effects. A smaller vocabulary will give you a lower IQ. There are likely to be other factors affected by exposure to wider experiences than you might not get when impoverished; for example, in general, the more you handle numbers, the better you get at manipulating them.
Highly educated people might also have higher innate intelligence, which allows them to pick up words easier and develop larger vocabularies. Let's not forget that IQ has been shown to be significantly heritable by adoption studies.
