Tag Archives: IQ

The conflation of family and population helps explain why the Nature vs. Nurture formulation persists II (revised)

Revised version

The first installment ended on the following note: Suppose you have many sets of same-sex non-identical twins raised together and many sets of same-sex identical twins raised together and find that the identical twins are on average more similar.  It seems reasonable to conclude that is because they share all their genes whereas the non-identical twins share fewer of their genes.  Reasonable, but not certain, at least not certain that it is only about genes.  After all, the treatment of identical twins could be more similar than the treatment of non-identical twins, even same-sex non-identical twins.  In any case, that conclusion doesn’t say that it’s the same nature—the same genes—or the same nurture that brings about the resemblance from one pair of twins to the next.  Given this possibility of underlying heterogeneity where are you?  What can you do? Continue reading

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A lesson in race, genes, and IQ

“Some people suggest that race is coded in genes and genes determine IQ test scores. A slightly less simple but similar supposition is that differences among races are associated with differences in genes that people have, which, in turn, are associated with differences in IQ test scores. Yet everyone has a sense that such claims are controversial. What should you think about them?”

With this introduction I kicked off an interactive presentation to high school students visiting the exhibit “Race: Are We So Different” at the Museum of Science in Boston in 2011. In preparing the talk I had been concerned that the efforts of many critics to counter claims that link race, genes, and IQ test scores were too easily discounted by people entertaining the hypothetical: “Suppose that one day advances in genetics show direct links…” So I wanted not to assert from a position of professorial authority that this or that scientist was wrong about the facts or interpretations. I sought instead to render simple direct relationships implausible and to provide angles of critical questioning that would help students respond to any new facts that might emerge in the future. In this spirit, the presentation started with the introduction above, announced the take-home lesson – “The world is not that simple” – then moved through the script reproduced below. I do not have data to show how successful I was, so let me suggest that readers evaluate the educational approach for themselves by formulating their own answers at each step. At the end, see whether you have a clearer sense of why it is implausible that race, genes, and IQ test scores can be linked in any direct fashion…  [See more]

An (imaginary) exchange with Eysenck about meritocracy

Taylor [T]: Why are you so concerned about genetic determination of mental ability?

Eysenck [E]: If abilities are determined by birth and society can predict who will be naturally talented, then it can allocate its resources more efficiently, for example, through separation of school children into separate tracks.

T: Why not test young people and use the results to make such predictions—then we can forget the issue of where their abilities originate?  You have, after all, been a life-long proponent of mental testing.

E: If abilities are biologically inherited and society is meritocratic, then elites are biological elites.

T: And so…?

E:  Rather than wait until children are old enough to be tested for intelligence, we can allocate resources from birth onward according to their parents’ status.

T:  High status parents already do that.  Wouldn’t someone who does not believe in meritocracy—someone who prefers a system that perpetuates privilege—also support the practice you propose?

E: The difference is that I would use intelligence tests at eleven, sixteen, and so on to check that the right children have been placed on the advanced tracks.

T:  Then, again, why not simply use such testing and forget the heredity issues?—especially given that parental intelligence is an imperfect predictor of offspring intelligence.

E:   Even if starting to track children at an early age leads to some errors, it is probably a more efficient allocation of educational resources.

T:  Efficient for whom?—You must know that tracking in practice means more than providing different kinds of education;  time and again it has resulted in unequal allocation of resources (Oakes 2005).

E:  That does not have to be the case.

T:  Maybe not, but unless you can show that unequal allocation has never been the case in the past, how could you show that the current “pyramidal structure” of society is due to “inherited inequalities in mental ability”?

Extracted fromTaylor, P. “Why was Galton so concerned about ‘regression to the mean’? -A contribution to interpreting and changing science and society” DataCritica, 2(2): 3-22, 2008, http://www.datacritica.info/ojs/index.php/datacritica/article/view/23/29.

Reference

Oakes, J. (2005) Keeping track: How schools structure inequality. New Haven: Yale University Press.

Conceptual starter kit for thinking about genes, race, and IQ test scores II

For the purposes of looking at the second question (from the first post), “Does this make you think that differences among IQ scores between races are genetic?,” let’s accept that the answer to the first question, “What does it mean to say IQ test scores are largely genetic?” is that something called heritability is high for IQ test scores.

In the USA we see persistent large differences in average IQ test score exist between racial groups.

Why?  (asking for audience input)

But no environmental factor, or composite of factors, seems to be associated strongly with the group average differences (Flynn 2007; but see Fryer and Levitt 2004).

This has led some researchers to make a two-part argument: the high heritability of IQ test scores within racial groups coupled with a failure of environmental hypotheses to account for the group differences supports—or lends plausibility to—explanations of mean differences in terms of genetic factors (even if these factors have yet to be elucidated) (e.g., Jensen in Miele 2002, 111ff).

Does this seem plausible to you? (waiting for audience input)

Consider this additional information.

Flynn ( 1994) has pointed to large gains in average IQ test score between generations in developed countries (now called the Flynn effect).

No environmental factor, or composite of factors, such as diet or years of education, has been shown to be associated strongly with the generational differences.

Now bring in the two-part argument: the high heritability of IQ test scores within groups coupled with a failure of environmental hypotheses to account for the group differences supports—or lends plausibility to—explanations of mean differences in terms of genetic factors.

If we look at each generation as a distinct group, the two-part argument means we should favor explanations of generational differences in terms of genetic factors, yet the change in gene frequencies in a human population over one generation is negligible.

Conclusion?  The logic of the two-part argument must be flawed and must be put aside.

That leaves us still having to explain large differences between generations—or racial groups—in a highly heritable trait.  That ” IQ paradox” is a discussion for another time.

References

Flynn, J.R.: 1994, IQ Gains over Time, in R. J. Sternberg (ed.), Encyclopedia of Human Intelligence, Macmillan, New York, pp. 617-623.

Flynn, J.R.: 2007, What is Intelligence? : Beyond the Flynn Effect. Cambridge University Press, Cambridge.

Fryer, R. and Levitt, S.: 2004, Understanding the Black-White Test Score Gap in the First Two Years of School. The Review of Economics and Statistics, 86(2), 447-464.

Miele, F.: 2002, Intelligence, Race, and Genetics: Conversations with Arthur Jensen, Westview Press, Boulder, CO.

Conceptual starter kit for thinking about genes, race, and IQ test scores

“What does it mean to say IQ test scores are largely genetic?  Does this make you think that differences among IQ scores between races are genetic?”  Starting with these two questions, I aim to get an audience of high school students thinking about the three areas that make up this sequence of posts.  Comments welcome about how to revise this approach so as to provide a “conceptual starter kit for thinking about genes, race, and IQ test scores.“

A. First question, “What does it mean to say IQ test scores are largely genetic?” (asking for audience input and filling in the following sequence of answers and “buts”)

Possible answers:

1. Genes cause IQ more than environment does. But how to separate these—everyone also needs an environment to survive and grow.

2. If your parents are above-average IQ, you are more likely to be above average.  But parents also pass on environment (educational options, etc.)

3. Differences in genes from one person to the next have more influence on IQ than differences in environment.  But how do you track the influence of genes without knowing which of our 30,000 genes influence IQ, and even worse for environmental factors.

4. If you and your identical twin were separated at birth and raised in difference families, you’d be more similar than any two random people raised in different families.  But these situations are very rare (and not necessarily at birth and not necessarily in independent families).

5. If your sibling is adopted into a professional family but you grow up poor and you end up with same IQ.  But this is not on average true—usually there’s a strong boost in IQ for the adopted child.

6. Identical twins raised in the same family are more similar on average than non-identical twins raised in same family.  Remember, identical twins share all their genes, but non-identical do not, so the increased similarity corresponds to sharing more genes.  This answer seems better (although not without critics).  It is on this basis researchers say IQ has a “heritability” of 60-80%.

(Note: Here heritability is a technical term with a quite different meaning from the idea that something is heritable if there is a gene that gets transmitted from parent to offspring.)

Continued in the next post.

The conflation of family and population helps explain why the Nature vs. Nurture formulation persists II

The first installment ended on the following note: Suppose you have many sets of same-sex non-identical twins raised together and many sets of same-sex identical twins raised together and find that the identical twins are on average more similar.  It seems reasonable to conclude that is because they share all their genes whereas the non-identical twins share fewer of their genes.  However, that conclusion doesn’t say that it’s the same nature—the same genes—or the same nurture that brings about the resemblance from one pair of twins to the next.  Given this possibility of underlying heterogeneity where are you?  What can you do?

You might take the results of the multiple twins study and transfer them back into thinking about your family.  Suppose that the non-identical twins are very much less similar so that sharing fewer genes makes a big difference (skipping here the technicalities of getting the number, “heritability,” that quantifies that result).  If that is so, you might say: “There’s nothing I could do as a parent to change the outcome for my offspring (for whatever trait you’re thinking about, e.g., IQ test score).  I’m not to blame for the outcome (other than having passed on my genes).  If that seems justified to you, you might then reason that the same is true for every other family, and thus society as a whole shouldn’t try to change what it’s doing for it won’t make a difference.

Now flip that scenario. Suppose that the non-identical twins are just as similar so that sharing fewer genes makes little difference.  What can you do as a parent?  Or, if your offspring are grown, what could you have done?—What then can you advise others for the future, or society at large?  In this scenario, the possibility of underlying heterogeneity is a problem.  Your study of twins has not shown you what environmental factors have had an effect so you don’t know what to change.  And, if you can’t expect the factors to be the same from one family to the next, you might just give up on trying to identify those factors.

Notice an asymmetry in these scenarios. The possibility of underlying heterogeneity didn’t lead you to give up on looking for the genetic factors because your reasoning did not lead you to look for them at all.  You simply concluded that you weren’t to blame for the outcome in your family and, by extrapolation, society shouldn’t try to change what it’s doing.

Now there’s a problem in the reasoning that says because sharing fewer genes makes a big difference there’s nothing a parent can do to make a difference.  Any set of twins, call it set i, is raised together in family i—each nature i has a nurture i.  There are lots of i’s.  There is nothing in the average over many sets of nature i – nurture i pairs that says there cannot be a nurture j or k or l in which nature i in nurture j or k or l wouldn’t be different in interesting ways.  Perhaps if you found that identical twins raised apart were just as similar on average as identical twins raised together, you’d doubt that such a nurture j or k or l could be found.  You’d doubt, but not be sure.  You could be surprised. Japanese offspring after WWII grew taller on average than their parents, but a comparison of twins in the previous generation woud have shown that sharing fewer genes makes a big difference (i.e., heritability for height was high).

Once you entertain the possibility that nature i varies across nurture i, j, k, l, … you can ask about what genetic factors and what environmental factors are involved and how they act together.  Now there is a symmetry in how difficult it is to identify those factors if you cannot expect them to be common across families.  Some responses to this difficulty are taken up in the next installment.