2. Galton (1888) observed a brain size/cognitive ability relationship. Modern MRI imaging has confirmed a positive correlation. Recently Richard Haier, at Brain Research Institute, UC Irvine College of Medicine, found that general human intelligence appears to be correlated with the volume and location of gray matter tissue in the brain.
For a summary of the neurobiological correlates with 'g' see Thompson & Gray's summary: http://www.loni.ucla.edu/~thompson/PDF/nr
See this article in New Scientist dated 11 March 2009, discussing the recent twin studies on myelination & intelligence:
" By comparing brain maps of identical twins, which share the same genes, with fraternal twins, which share about half their genes, the team calculate that myelin integrity is genetically determined in many brain areas important for intelligence. This includes the corpus callosum, which integrates signals from the left and right sides of the body, and the parietal lobes, responsible for visual and spatial reasoning and logic (see above). Myelin quality in these areas was also correlated with scores on tests of abstract reasoning and overall intelligence (The Journal of Neuroscience, vol 29, p 2212).
Just because intelligence is strongly genetic, that doesn't mean it cannot be improved. "It's just the opposite," says Richard Haier, of the University of California, Irvine, who works with Thompson. "If it's genetic, it's biochemical, and we have all kinds of ways of influencing biochemistry."
3. Gould's criticism of factor analysis (and 'g') is flawed: see John Carroll's review Intelligence 21, 121-134 1995 and also Jensen Contemporary Education Review Summer 1982, Volume 1, Number 2, pp. 121- 135.
David J. Bartholomew, from London School of Economics, who has written a textbook on factor analysis, also explains in "Measuring Intelligence: Facts and Fallacies" explains where Gould goes wrong in this area.
4. Gould suggests that Jews tested poorly in the 1920's & this lead to the Immigration Act 1924. Both are incorrect.
5. The idea that Jews tested poorly is actually based on a misrepresentation of a paper authored by Henry Goddard in 1917. Goddard gave IQ tests to people suspected of being mentally handicapped. He found the tests identified a number of such people from various immigrant groups, including Ashkenazi Jews. Leon Kamin in 1974 reported that Goddard had found Jews had low IQ scores. However, Goddard never found that Jews or other groups as a general population had low scores. There is other information that contradicts the idea that Jews did poorly on IQ tests around this time. In 1900, in London, Jews took a disproportionate number of academic prizes in spite of their poverty (C Russell & H.S. Lewis 'The Jew in London' Harper Collins 1900). Also, note that by 1922 Jewish students made up more than a fifth of Harvard undergraduates & the Ivy League was already instituting policies aimed at limiting Jewish admissions (the infamous 'Jewish quotas'). Also, a 1920's a survey of IQ scores in three London schools with mixed Jewish & non-Jewish student bodies - one prosperous, one poor and one very poor - showed that Jewish students, on average, had higher IQ's than their schoolmates in each of the groups (A Hughes 1928).
- see also: G. Cochran, J. Hardy, H. Harpending, Natural History of Ashkenazi Intelligence, Journal of Biosocial Science 38 (5), pp. 659-693 (2006).
6. The other misconception is that this contributed to the 1924 Immigration Act. However, Herrnstein & Snyderman found this was not the case (Intelligence Tests and the Immigration Act of 1924' American Psychologist 38, September 1983).
7. Although it was claimed Cyril Burt made up data for his twin studies, subsequent investigations have cast doubt on this. See the book Cyril Burt 'Fraud or Framed', edited by Nick Mackintosh former Chair of Psychology at the University of Cambridge.
8. Burt's findings regarding hereditary appear to be very consistent with subsequent twin studies. Steven Pinker wrote in the NY Times earlier this year:
"To study something scientifically, you first have to measure it, and psychologists have developed tests for many mental traits. And contrary to popular opinion, the tests work pretty well: they give a similar measurement of a person every time they are administered, and they statistically predict life outcomes like school and job performance, psychiatric diagnoses and marital stability. Tests for intelligence might ask people to recite a string of digits backward, define a word like "predicament," identify what an egg and a seed have in common or assemble four triangles into a square.
The most prominent finding of behavioral genetics has been summarized by the psychologist Eric Turkheimer: "The nature-nurture debate is over. . . . All human behavioral traits are heritable." By this he meant that a substantial fraction of the variation among individuals within a culture can be linked to variation in their genes. Whether you measure intelligence or personality, religiosity or political orientation, television watching or cigarette smoking, the outcome is the same. Identical twins (who share all their genes) are more similar than fraternal twins (who share half their genes that vary among people). Biological siblings (who share half those genes too) are more similar than adopted siblings (who share no more genes than do strangers). And identical twins separated at birth and raised in different adoptive homes (who share their genes but not their environments) are uncannily similar."