This fallacy uses evidence of any fluctuation or growth in the mental functioning of individuals as if it were proof that their rates of growth can be changed intentionally. IQ level is not made malleable by any means yet devised (Brody, 1996), ..."
- Linda Gottfredson, Logical fallacies used to dismiss the evidence on intelligence testing http://www.udel.edu/educ/gottfredson/reprints/2009fallacies.... (PDF page 24)
Losing a tire in my car won't make me lose any horsepower, but it's not going to be the same ride.
Actually, the view of behavioral geneticists, including those with whom I have a weekly discussion of current research,
http://www.psych.umn.edu/courses/fall09/mcguem/psy8935/defau...
is that each individual has a "reaction surface," a range of possible behavioral responses genetically endowed for that individual depending on what environmental influences that individual encounters. NO ONE active in the field of behavorial genetics claims to have proved that many individuals today have maxed out their potential for intelligent behavior. There may be (as yet unknown) interventions that could massively change IQ at the individual level.
This is most likely because children in Head Start become more familiar with IQ test style problems and a testing environment. In short, Head Start (presumably unintentionally) teaches the test.
http://www.eric.ed.gov/ERICDocs/data/ericdocs2sql/content_st...
(Scroll to page 65)
Yes, this is a correct statement. The design of studies to determine a numerical figure for the pre-Mendelian concept of "heritability" can only show a MINIMUM influence of environment, and the minimum influence of environment on IQ is fairly large. Most heritability studies are, by their nature, naturalistic rather than experimental studies and prove nothing about what degree of malleability (a separate issue anyway) might be found if an experimenter tried targeted environmental interventions. And, yes, there are monozygotic twins who are discordant for IQ, so there must be influences other than genes on IQ.
IQ scores are sufficiently stable from one time of taking an IQ test to the next that most psychologists conclude that what is estimated by an IQ test can be regarded as a "trait" rather than a "state" of an individual test-taker. And yet IQ scores, especially in childhood, do vary over the course of a test-taker’s life, sometimes varying radically. Deviation IQ scoring was originally developed to make for more stability of scores over the course of childhood. Nonetheless, deviation IQs for children can also change considerably over the course of childhood (Pinneau 1961; Truch 1993, page 78; Howe 1998; Deary 2000, table 1.3). "Correlation studies of test scores provide actuarial data, applicable to group predictions. . . . Studies of individuals, on the other hand, may reveal large upward or downward shifts in test scores." (Anastasi & Urbina 1997 p. 326).
For example, young people in the famous Lewis Terman longitudinal Genetic Studies of Genius (initial n=1,444 with n=643 in main study group) when tested at high school age (n=503) were found to have dropped 9 IQ points on average in Stanford-Binet IQ. More than two dozen children dropped by 15 IQ points and six by 25 points or more. Parents of those children reported no changes in their children or even that their children were getting brighter (Shurkin 1992, pp. 89-90). Terman observed a similar drop in IQ scores in his study group upon adult IQ testing (Shurkin 1992, pp. 147-150). Samuel R. Pinneau conducted a thorough review of the Berkeley Growth Study (1928-1946; initial n=61, n after eighteen years =40). Alice Moriarty was a Ph.D. researcher at the Menninger Foundation and describes in her book (1966) a number of case studies of longitudinal observations of children's IQ. She observed several subjects whose childhood IQ varied markedly over the course of childhood, and develops hypotheses about why those IQ changes occurred. Anastasi and Urbina (1997, p. 328) point out that childhood IQ scores are poorest at predicting subsequent IQ scores when taken at preschool age. Change in scores over the course of childhood shows that there are powerful environmental effects on IQ (Anastasi & Urbina 1997, p. 327) or perhaps that IQ scores in childhood are not reliable estimates of a child’s scholastic ability.
REFERENCES
Anastasi, Anne & Urbina, Susana (1997). Psychological Testing. Upper Saddle River, NJ: Prentice Hall.
Deary, Ian J. (2000) Looking Down on Human Intelligence: From Psychometrics to the Brain. Oxford: Oxford University Press.
Howe, Michael J. A. (1998). Can IQ Change?. The Psychologist, February 1998 pages 69-72.
Moriarty, Alice E. (1966). Constancy and IQ Change: A Clinical View of Relationships between Tested IQ and Personality. Springfield, IL: Charles C. Thomas.
Pinneau, Samuel R. (1961). Changes in Intelligence Quotient Infancy to Maturity: New Insights from the Berkeley Growth Study with Implications for the Stanford-Binet Scales and Applications to Professional Practice. Boston: Houghton Mifflin.
Shurkin, Joel N. (1992). Terman's Kids: The Groundbreaking Study of How the Gifted Grow Up. Boston: Little, Brown.
Truch, Steve (1993). The WISC-III(R) Companion: A Guide to Interpretation and Educational Intervention. Austin, TX: Pro-Ed.
"If American children of 1932 could take an IQ test normed in 1997 their average IQ would have been only about 80.[2] In other words, half of the children in 1932 would be classified as having borderline mental retardation or worse in 1997." (http://en.wikipedia.org/wiki/Flynn_effect)
Your confusion arises from treating correlation as causation. Mental retardation is commonly caused by genetic or developmental problems that cause global brain changes, producing deficits in many or all talents. This usually includes the specialized brain circuits involved in symbolic reasoning, lowering the IQ. So in a population with shared genes and environment, low IQ is strongly correlated with mental retardation, but neither is caused by the other.
"Either our ancestors were dullards, or the IQ test measures something other than innate intelligence."
The Flynn effect proves what we already knew, that human development is partially driven by the environment. Few serious scientists thought that each human is born with a exact fixed amount of smarts, like every atom of iron-56 has 55.93 AMUs of mass.
To add to that fire, I also don't believe that GPA has much to tell about someone's performance and capabilities (don't get me wrong, in some ways it does, but now how companies like Google use it to "weed" out applicants).