Freethought & Rationalism Archive

ps418 · 10-26-2002, 06:29 AM

I found 2 interesting articles relating to the relationships between genetics, brain volume, and intelligence. It doesn't specifically address the OT of this thread, but then it doesn't quite justify a new thread either. It would seem from these studies (as with the earlier studies I cited) that the genetic lottery has given some people a substantial initial advantage when it comes to intelligence.

The article by Thompson et al (2001) reports data from 40 subjects, 2 pairs each of identical and fraternal twins. Grey matter volume was determined for several brain regions using 3D MRI images. Cognitive tests consisted of 17 Wechsler Adult Intelligence Scale domains, including verbal and spatial working memory, selective and divided attention, verbal knowledge, motor speed, and visuospatial ability. They report a correlation of 0.37-0.40 between frontal grey matter volume and IQ. Plomin and Kosslyn (2001) in their commentary on Thompson et al state that the results [/i]"suggest that 'g' is not simply a statistical abstraction that emerges from factor analyses of psychometric tests; it also has a biological substrate in the brain"[/i] (Genes, brain and cognition, Nature neuroscience 4, p. 1154). They also cite 14 earlier studies of ~700 individuals in which correlations between brain volume and 'g' are roughly 0.4 (Vernon et al, in Handbook of Intelligence (ed. Sternberg, R.J.) 254-264, Cambridge University Press, 2000), and argue that Thompson et al underestimate the association of 'g' with individual brain regions due to the assumptions in their statstical analysis. The Posthuma et al (2002) data includes 258 Dutch subjects, and also used the Wechsler Adult Intelligence Scale to assess IQ and MRI scans to assess grey matter volume. They report a correlation of 0.25 between IQ and total brain grey matter volume.

One clarification. A lot of the media blurbs describing the Thompson et al paper say things like 'genes determine IQ, scientists say,' which is obviously not quite correct. The correlation of grey matter volume among monozygotic twins is almost perfect, like 0.9. But the correlation between grey matter volume and IQ is about 0.3-0.4, still a very significant correlation of course, but hardly one that supports a rigid more-brain=more intelligence.

Thompson PM, Cannon TD, Narr KL, van Erp T, Poutanen VP, Huttunen M, Lonnqvist J, Standertskjold-Nordenstam CG, Kaprio J, Khaledy M, Dail R, Zoumalan CI, Toga AW, 2001. Genetic influences on brain structure. Nature Neuroscience 4(12):1253-8.

<a href="http://www.loni.ucla.edu/~thompson/MEDIA/NN/genetics_article_NN.pdf" target="_blank">http://www.loni.ucla.edu/~thompson/MEDIA/NN/genetics_article_NN.pdf</a>

Quote:

Here we report on detailed three-dimensional maps revealing how brain structure is influenced by individual genetic differences. A genetic continuum was detected in which brain structure was increasingly similar in subjects with increasing genetic affinity. Genetic factors significantly influenced cortical structure in Broca's and Wernicke's language areas, as well as frontal brain regions (r2(MZ) greater than 0.8, p less than 0.05). Preliminary correlations were performed suggesting that frontal gray matter differences may be linked to Spearman's g, which measures successful test performance across multiple cognitive domains (p greater than 0.05). These genetic brain maps reveal how genes determine individual differences, and may shed light on the heritability of cognitive and linguistic skills, as well as genetic liability for diseases that affect the human cortex.

Posthuma D, De Geus EJ, Baare WF, Hulshoff Pol HE, Kahn RS, Boomsma DI. , 2002. The association between brain volume and intelligence is of genetic origin.
Nature Neuroscience 5(2):83-4.

Patrick

ps418 · 11-03-2002, 07:29 AM

Quote:

Echidna: Patrick, you quote the BC as "it seems highly likely to us that both genes and the environment have something to do with racial differences. What might the mix be? We are resolutely agnostic on the issue; as far as we can determine, the evidence does not yet justify an estimate".

OK I'm somewhat relieved, and yet Murray makes little or no effort to highlight this crucial distinction.

. . . I find it highly suspicious that Murray does not seem keen to distance himself from this claim, certainly amongst the most common criticism levelled against him. He does not clarify it in either lengthy post-BC article.

Actually, Murray did reiterate his opinion in post Bell Curve interviews and articles. For instance, in his article <a href="http://www.mugu.com/cgi-bin/Upstream/People/Murray/bc-crit.html" target="_blank">"The Bell Curve" and its critics, Commentary, May 1995 v99 n5 p23(8), </a> Murray stated that:

Quote:

For the record, what we said about genes, IQ, and race in the book is that a legitimate scientific debate is under way about the relationship of genes to race differences in intelligence; that it is scientifically prudent at this point to assume that both environment and genes are involved, in unknown proportions(4);

Footnote 4 states:

Quote:

4) Intelligence is known to be substantially heritable in human beings as a species, but this does not mean that group differences are also heritable. Despite our explicit treatment of the issue, it is perhaps the single most widespread source of misstatement about The Bell Curve.

[ November 03, 2002: Message edited by: ps418 ]

echidna · 11-10-2002, 07:53 PM

Patrick, apologies for a lengthy delay but I�ve been preoccupied in other threads.

Quote:

Originally posted by ps418:
Actually, Murray did reiterate his opinion in post Bell Curve interviews and articles. For instance, in his article "The Bell Curve" and its critics, Commentary, May 1995 v99 n5 p23(8), Murray stated that:

quote:
------------------------------------------------------------------------
For the record, what we said about genes, IQ, and race in the book is that a legitimate scientific debate is under way about the relationship of genes to race differences in intelligence; that it is scientifically prudent at this point to assume that both environment and genes are involved, in unknown proportions(4);
------------------------------------------------------------------------

Footnote 4 states:

quote:
------------------------------------------------------------------------
4) Intelligence is known to be substantially heritable in human beings as a species, but this does not mean that group differences are also heritable. Despite our explicit treatment of the issue, it is perhaps the single most widespread source of misstatement about The Bell Curve.

Granted, but not perhaps �the single most widespread source of misstatement about The Bell Curve�, but *the* most widespread source of misstatement about The Bell Curve�.

Despite Murray�s claim of indignation at this misapprehension about his book, it�s safe to say that the majority of people misread what the Bell Curve says. At best he is guilty of incompetence in failing to adequately clarify such an important issue, at worst he is complicit in misleading his audience towards a high genetic link between race & IQ by couching his position in footnotes (thank you for your superior attentiveness).

Largely this would seem come down to the IQ tests which we have already discussed. It would seem that despite numerous claims that Raven�s Tests and such are culture-free or culture-fair, they are not recognised as culture-neutral or footnote 4 would not be necessary.

When I initially began reading on this subject I assumed that claims that IQ tests could be designed culture-free, since that seemed to be the widespread claim. However I think now I would prefer the term culture-reduced than free or fair.

Indeed Murray says �Insofar as the tests are biased at all, they tend to overpredict, not underpredict, black performance.�

Statements like this are not conducive to the agnosticism of the cause for the gap between population means.

P1. There is a 10 point difference between blacks and whites in culture-free IQ tests.
P2. IQ is substantially genetic.

C1. The 10 point gap between races is substantially genetic.

You see, for simpletons like me, it is not immediately apparent why I cannot make C1, because I have falsely assumed the cultural-freedom of IQ tests, & as far as I can tell, Herrnstein-Murray go nowhere near enough to clarify this crucial point.

You may differ that Herrnstein-Murray were indeed entirely clear enough that there is no evidence of a genetic cause for the gap between means, however I would be comfortable to agree to disagree on this minor point.

Thank you for your assistance on this topic.

[ November 10, 2002: Message edited by: echidna ]

echidna · 11-10-2002, 09:21 PM

In fact for an ironic twist, from

<a href="http://www3.cosmiverse.com/news/science/0702/science07230202.html" target="_blank">http://www3.cosmiverse.com/news/science/0702/science07230202.html</a>

Quote:

The other study looked at brain size in people with autism aged 8 to 46 years old. When compared with others in that same age range that did not have autism, they found that in people younger than twelve, the autistic subjects had a 5% larger brain volume. After the age of 12, brains in the two groups were similar in size-but those with autism had heads that measured 1% to 2% larger than the non-autistic group.

These two studies are very significant in understanding the causes of autism, said Minshew. "They establish that there is a premature overgrowth of the brain in the first 2 years of life and then brain growth essentially plateaus in autism," she said. "By adolescence, it is the same as in normal individuals because of brain growth in the normal population." She noted that the adults with autism had increased head circumference, suggesting that their brain volume had been larger when they were children.

� which cannot help but be compared with the (formerly ?) infamous practices of phrenology.

ps418 · 11-11-2002, 12:13 PM

Quote:

Originally posted by echidna:
Patrick, apologies for a lengthy delay but I�ve been preoccupied in other threads.

Please take your time, and respond at your own pace. I will do the same.

Quote:

Despite Murray�s claim of indignation at this misapprehension about his book, it�s safe to say that the majority of people misread what the Bell Curve says.

That depends entirely on which population of readers you are sampling. Amongst the general population, that is undoubtedly true. But I don't think that the misreading can be so easily blamed on the authors, who appear to have carefully choosen their words.

Quote:

Largely this would seem come down to the IQ tests which we have already discussed. It would seem that despite numerous claims that Raven�s Tests and such are culture-free or culture-fair, they are not recognised as culture-neutral or footnote 4 would not be necessary.

This is an empirical question: What evidence do you have that Raven's matrices are not recognized (by experts in psychometry) as culture-fair? This does not agree with what I've seen in psychology journals. And if they are unfair, to what extent are they unfair, and who are they biased against? And are their any psychometric measures of intelligence that you regard as culture-fair?

Also, I am baffled about your commment regarding footnotes and Raven's matrices. How does the footnote #4 in the Murray article ("The Bell Curve and its Critics") I quoted justify your belief that Raven's matrices are not recognized as culture-fair?

Quote:

You may differ that Herrnstein-Murray were indeed entirely clear enough that there is no evidence of a genetic cause for the gap between means, however I would be comfortable to agree to disagree on this minor point.

You are of course free to disagree. But, to reiterate the opinion of the authors again, they did not say that there is no evidence that the IQ gaps between ethnic groups are entirely non-genetic. They simply say that they think that both environmental and genetic factors are likely involved, in unknown proportions. This is fully consistent with mainstream scientific opinion on the sources of between-group differences in cognitive abilities.

Finally, I am curious as to what hypothetical evidence you would accept as supporting a partial genetic basis for between-group differences in cognitive ability. I dont really know enough about the issue to say what would convince me one way of the other, but then again I am not comfortable just pronouncing a priori that none of the difference can be related to genes.

Quote:

Thank you for your assistance on this topic.

Thank you Echidna.

Patrick

ps418 · 11-11-2002, 12:19 PM

Quote:

Originally posted by echidna:
In fact for an ironic twist, from
. . . which cannot help but be compared with the (formerly ?) infamous practices of phrenology.

Forgive my density, but what is the irony here, and what is it that is being compared to phrenology?

Patrick

ps418 · 11-11-2002, 01:08 PM

Echidna,

I just found this abstract. You might find it interesting.

Quote:

The intelligence quotient (IQ) differs for various racial-ethnic groups. Blacks and Whites, for example, differ, on the average, by about 15 points in IQ. The present study finds that differences in knowledge between Blacks and Whites for items tested on an intelligence test, the meanings of words, can be eliminated. They are eliminated when equal opportunity for exposure to the information to be tested has been experimentally assured. The data support the view that cultural differences in the provision of information may account for racial differences in IQ.

Equal opportunity and racial differences in IQ. Intelligence, Vol. 30 (4) (2002) pp. 361-387

Looks interesting. I'll pick up a copy on my next trip to the library, and post a summary at some point.

beausoleil · 11-11-2002, 01:20 PM

Quote:

Originally posted by echidna:

Nonetheless, a full 13 points between Germany and France sharing a common border ??? Bearing in mind that these are culture-free tests

Surely the obvious conclusion is that they aren't culture free at all.

ps418 · 11-11-2002, 02:08 PM

Actually, I don't think that conclusion is so obvious.

I looked at the page purporting to show a 13 point IQ difference between France and Germany, which references a 20+ year-old article in the journal Personality and Individual Differences. It does not include any information on the populations that were tested, so any claim about what this wide gap shows or does not show is pretty much pure speculation.

And more importantly, more recent research assessing "national IQs" for countries using Progressive Matrices does not show a 13 point gap between France and Germany. Instead, it shows a 4 point gap [Germany=102; France=98]. See <a href="http://fp.rlynn.plus.com/pages/article_intelligence/t4.htm" target="_blank">this page showing national IQs for 185 countries.</a> From Richard Lynn and Tatu Vanhanen's <a href="http://fp.rlynn.plus.com/pages/article_intelligence/1.htm" target="_blank">Intelligence and the Wealth and Poverty of Nations (2000).</a>

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11-11-2002, 02:08 PM	#89
ps418 Veteran Member Join Date: Mar 2001 Location: Louisville, KY, USA Posts: 1,840	Actually, I don't think that conclusion is so obvious. I looked at the page purporting to show a 13 point IQ difference between France and Germany, which references a 20+ year-old article in the journal Personality and Individual Differences. It does not include any information on the populations that were tested, so any claim about what this wide gap shows or does not show is pretty much pure speculation. And more importantly, more recent research assessing "national IQs" for countries using Progressive Matrices does not show a 13 point gap between France and Germany. Instead, it shows a 4 point gap [Germany=102; France=98]. See <a href="http://fp.rlynn.plus.com/pages/article_intelligence/t4.htm" target="_blank">this page showing national IQs for 185 countries.</a> From Richard Lynn and Tatu Vanhanen's <a href="http://fp.rlynn.plus.com/pages/article_intelligence/1.htm" target="_blank">Intelligence and the Wealth and Poverty of Nations (2000).</a>

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