Heritability, IQ, & Education


    The relative importance of environment and heredity in determining human traits such as intelligence and educability has long been debated.
For example, studies have repeatedly measured the difference between the IQ scores of black and white children in the United States as 15~20 points. Arthur Jensen (1923-), an educational psychologist at UC Berkeley, wrote a widely-discussed 1969 article in the Harvard Educational Review, entitled "How much can we boost IQ and scholastic achievement?" His conclusion was: not much. From studies of monozygotic and dizygotic twins and other data, Jensen estimated the within-group heritability (h2) of IQ test scores as h2 ~ 0.7. He concluded therefore that investment in educational enrichment was unlikely to affect such performance. Similar arguments were advanced by Richard Herrnstein and Charles Murray in "The Bell Curve" (1994), and J. Phillipe Rushton (U Western Ontario) in "Race, Evolution, & Behavior" (1997),

        IQ tests were originally invented to identify a range of mental acuity in children in need of special help to perform well in school: no particular significance was attached to the exact numerical values. The initial use was thus to direct resources towards persons who needed them. Use of actual numerical scores as a mean of ranking intellectual ability first gained wide use in screening of European immigrants (many of whom could not understand the language in which the test was administered), and US army recruits during World War One (many of whom had never held a pencil). This IQ testing was used as a means of discriminating among persons, and withholding resources from those regarded as "inferior." Misuse of these tests is discussed in Stephen Jay Gould's "The Mismeasure of Man", which was revised and reissued in 1996 in response to The Bell Curve.
Amongst other concerns,

       1) Unlike measures of height or weight, or tests of blood phenylalanine or serum cholesterol levels, it is highly questionable whether there exists an intrinsic brain function equivalent to the abstract concept of "intelligence". Although it is possible to devise and record scores from IQ tests, the assumption that attaching a number to an abstract concept makes it "real" is the reification fallacy. Historically, it was assumed that intellectual ability was directly correlated with brain size, and craniometric statistics were used to "prove" that certain social (e.g., criminals) or ethnic groups (e.g., African or American Blacks) had smaller brains and were therefore less intelligent. Currently, quantitative investigations of brain anatomy or neurological functions such as processing speed encounter the same limitation, that such measurable phenomena cannot directly estimate abstract 'intelligence.'

       2) IQ tests have been shown to do a good job at predicting aptitude for educational activities, as have other test batteries such as the SAT, MCAT, LSAT, and GRE (for aptitude in undergraduate, medical, law, and graduate schools, respectively). This is not surprising, because success in such activities is often measured in the same was as "IQ", by means of standardized tests. IQ test scores undoubtedly correlate with other performance indices that are generally regarded as desirable.

        3)
"Heritability is not the same as heredity: neither equals inevitability" The explicit or implicit assumption that genetically-influenced traits are constant and/or unalterable is scientifically fallacious. Heritability ( h2) as defined by geneticists is a specific statistical measure, the fraction of observed trait variance due to genetic variance. High heritability of agricultural production traits such as egg or milk quality mean that is possible to improve such traits by selective artificial breeding: demonstration of a high heritability for IQ test scores means only that it would be possible to breed selectively for improved performance on IQ tests. It is well-established that within-group heritability does not predict between-group heritability differences. High heritability also does not mean that a trait cannot be altered by a change in environment.

         4) Data from twin studies can be used to estimate heritability from the observed differences between identical and non-identical twins. IQ scores of the former are more highly correlated than those of the latter, as predicted by a heritability model.  However,
in such data sets it is extremely difficult to separate the effects of genetic relatedness ('heritability') from those of environmental similarity ('familiality'). For example, similarities of mother tongue and political party affiliation are highly correlated between parents and offspring, but are without genetic basis.

    Some of classic twin studies are highly questionable. The most famous proponent of educational testing in Britain, Sir Cyril Burt (1883-1971) is now known to have altered a great deal of his twin data in order to support his preferred conclusions. Burt's results were used for decades to channel children through the British educational system by use of standardized test to determine perceived inborn merit. More modern twin studies [e.g., the Minnesota Twin Study] continue to show high correlation between IQ scores and degree of relatedness.
Twins raised apart are markedly less similar than those raised together; similarities are sometimes striking, but are often overstated

        5) Periodic resurgence of interest in classification of humans or human groups as of lesser or greater intrinsic worth based on IQ  (or other "objective" tests) typically corresponds with times of social conservatism, as in post-World War I America, Germany in the 1930s, and the Reagen era of the 1980's. The history of the eugenics movement is particularly instructive. It has often served political agendas that promote "us versus them" thinking, and the allocation of scarce resources away from
particular groups, education, and/or other social programs, on the assumption that environmental modification can have no effect on "innate" group differences.


All text material 2014 by Steven M. Carr