"The statement, 'IQ is [partly] genetically determined,' ought to be qualified as, 'IQ is [partly] genetically determined, given the levels of genetic and environmental variability in the population.' "

I don't follow. Adding this qualification would seem redundant because merely restating the obvious. The claim in question ALREADY IS that IQ is PARTLY genetically-determined, which intrinsically means "regardless of whatever environmental factors may exist." The extent to which it's NOT genetically determined gives some idea of the extent to which environment may influence it. It cannot influence it beyond that extent, according to these studies. The studies whereon this is based controlled for environmental factors, which is how they arrived at their conclusion in the first place.

Of course, "character" is an important factor in life, one whose relationship with IQ isn't completely clear (one senses it must be partly related but only partly, and it would seem to be more molded by environment than IQ is). While character can't overcome the importance of IQ, its importance relative to certain specific genetic endowments (probably including IQ) was illustrated two thousand years ago by Aesop, in the fable of the tortoise and the hare.

The hare, blessed with a genetic advantage for running fast, lost the race to the tortoise who, though cursed with a genetic disadvantage at running fast, nevertheless possessed a character advantage.

The importance of character was the basis on which Pat Buchanan pooh-poohed the significance of the book, "The Bell Curve," on "The McLaughlin Group" shortly after publication. Aesop and Buchanan are right that genetic endowment isn't everything, whether that endowment be in regard to IQ or, for example, to natural running ability. But it is of course important, decisively so in many ways.

"If GENESA=GENESB (as in identical twins) then 100% of the [IQ difference] will be environmental. ... [Conversely, the more similar the environments, the more any observed IQ differences will be due to inborn differences in genetic endowment.] ... As the variability of one of the inputs (ENVIRONMENT or GENES) decreases (in the limit becomes 0!), the variability of the outcome (IQ) becomes [more] dependent on that of the 'other' input."

So far, so good. But the final conclusion drawn doesn't follow from what went before:

"So, there's no hard limit on the proportions of dependence of IQ on genes and environment. It all depends on the variability of the input parameters."

This doesn't follow. The IQ studies in question have shown that variation in "environmental factors" (a term which merely means "all factors aside from genetic ones") cannot amount to more than a twenty-percent-to-fifty-percent influence on IQ. So, the most that IQ can be affected by even the most radically different environmental conditions is this twenty-to-fifty-percent figure. It's wrong that there is "no hard limit on the proportions of dependence of IQ on genes and environment" and I don't see where anything said above changes this. This fifty-to-eighty-percent figure for the influence of genes on IQ is exactly part of that "hard limit" (the remainder, of course, being the maximum possible influence on IQ of environment).

"... estimates of genetic influence [on] IQ in a given population cannot be applied to genetic influence [on] IQ in another population."

This is a bold statement. Nothing said above disproves the contrary assumption that the results of the IQ studies in question apply to people in general, not just to the testing subjects' particular races or nationalities to the exclusion of other races and nationalities.

"... [T]he USA has a certain level of genetic and environmental variability. The world at large has higher levels of both genetic and environmental variability."

To the extent that this can be interpreted (a bit vague, but I think I've got it): OK -- so far so good.

"If we determine that IQ is x% genetically determined in the US, that does not imply that it is also x% genetically determined in the world at large."

There is no reason to think the twin studies and other research which form the basis for the proof of the heritability of IQ don't apply to races/nationalities (or whatever) other than those of the people who were actually studied.

This doesn't follow. The IQ studies in question have shown that variation in "environmental factors" (a term which merely means "all factors aside from genetic ones") cannot amount to more than a twenty-percent-to-fifty-percent influence on IQ.

That is incorrect. THe IQ studies have shown that the effect that environmental factors have currently is at most x%, but they have not shown that x% is an upper limit on their potential effect.

Let's give a simplified example. Suppose that there are three ways to raise a child, a GOOD, a COMMON, and a BAD way. An identical genotype, exposed to the GOOD influence will have an IQ of x+10; to the COMMON x; to the bad, of x-10.

Also, assume that the genotype, which controls the level "x" is normally distributed, say with mean 100. Now, in this setup, by examining a population who is subjected to the GOOD/COMMON/BAD way, we can quickly determine that there are hard limits to how much we can raise or diminish the population mean. I.e., we cannot raise it above 110, or diminish it below 90.

But, if tomorrow the GOOD way of upbringing is abandoned, then the mean IQ may only be made to range between 90 and 100. Conversely, if an EXCELLENT way of upbringing is discovered which confers an advantage of +30, then the population could acquire a mean IQ as high as 130, e.g., if everyone starts raising their children in the EXCELLENT way.

Thus, I stress that the x% genetic refers always to a given genetic/cultural situation, and says absolutely nothing about the potential that nurture may have on IQ in the future inasmuch as it cannot quantify the effect on IQ of currently unknown cultural practices.

This is a bold statement. Nothing said above disproves the contrary assumption that the results of the IQ studies in question apply to people in general, not just to the testing subjects' particular races or nationalities to the exclusion of other races and nationalities.

Indeed, my statement is correct. To see why this is the case, imagine a population that has extremely low genetic variability (in the limit: zero genetic variability - identical twins). In that case, most of the observed variability (in the limit: all) will be due to environment.

Conversely, imagine an Orwellian scenario in which every individual is subjected to exactly the same set of influences. In that case, the environmental variability is zero, and all the observed variability will be due to genes.

There is no reason to think the twin studies and other research which form the basis for the proof of the heritability of IQ don't apply to races/nationalities (or whatever) other than those of the people who were actually studied.

I have explained above why in fact one cannot generalize from a given population group to other population groups.