Questions on _g_ and intelligence

[Mandrake]

However, I am still somewhat in the dark about _g_ and the individual; specifically, the +/- which psychometricians (in the field as well as in well appointed labs) assign to the results from just one test, of each kind (IQ, chronometric, EEG). Your comparisons with some tests done in doctors' offices is quite apt - and I'd like to explore this some more.

As I attempted to explain before, the errors associated with any measurement are a function of the measurement tool. It is also possible to combine measurements when their variances add. This is done with individual test items and is done with individual elementary cognitive tests. One would expect that a more heavily _g_ loaded test would produce a more robust measurement than a less _g_ loaded one. The only way to get at the numbers you wish to find is to find them in the literature. The most through discussion of psychometric measurement tools that I have seen is Jensen's Bias in Mental Testing. There is some information in The _g_ Factor. There is, as I previously noted, a great deal of related information in most serious research papers that are based on measurements.

In doing good science, of course we expect that the administration of tests be done so as to eliminate or control for extraneous factors which may influence the effects we seek to collect data on. My question here is only with research results on the measured size and nature of each of the above effects (and any others which psychometricians have discovered) on an estimate of _g_, for each class of test (IQ, e.g. WAIS; chronometrics, EEG); preferably expressed as a range that could be expected in the result of just a single test.

You will have to dig it out of the literature, unless hitsquad happens to have some numbers handy. IQ tests typically correlate with _g_ at around .9 or so. In the case of the Raven's Jensen has commented that it is essentially a pure measurement of _g_, but naturally contains some loading on _e_. IQ test results are sometimes stated with an assigned range. You get the numerical value and a plus or minus range that corresponds to a stated confidence level. As you know, most statistically determined measures are stated in terms of probability and confidence level.

 

[Nereid]

The material you quoted was a press release. The comments I made were directed at the following:
Report of a Task Force established by the Board of Scientific Affairs of the American Psychological Association
Released August 7, 1995
A slighted edited version was published in the American Psychologist, Feb 1996.

Whew! Glad we cleared that up! Thanks Mandrake.

 

[Mandrake]

Perhaps I haven't been clear enough; the effects of test conditions, pre-test expectations, etc on estimates of _g_ wouldn't necessarily be to boost an estimate, they could depress it (e.g. the 'white coat effect' makes some people appear less healthy than they 'really' are).

All of the information I have seen indicates that, if the person is rested, healthy, etc. the test scores are not going to be significantly boosted or depressed by the testing environment. One obvious condition for testing is quite and freedom from outside distractions. We sometimes hear people commenting that an individual doesn't test well. In such situations, the most likely reason the person doesn't test well is that he is not as intelligent as he would like to believe.

The music and stress factors look interesting; how much research has been done on such factors when tests are done in the field (vs in well appointed labs)? How large was the 'music' effect?

There is information available on the effects of various factors, such as stress. As I recall the material from Jensen is in his textbooks. The effect of music first appeared in Nature in 1993 and was then called the Mozart Effect. It was touted by the press. Various reviewers contended that the claims were not valid. The issue did not go away. There have been additional reports, such as The Mozart Effect, From New Scientist, 6 November 1999. "For the sake of consistency, almost all studies on the Mozart Effect so far have focused on a single piece of music, the Sonata for Two Pianos in D Major (K 448), though some have measured the effect from other music as well. "It is not just this composition, and not just Mozart," says Rauscher. However, the researchers don't know why the Sonata in D works or which other pieces might."

 

[Mandrake]

As SAT scores correlate well with _g_ (or, as I'm beginning to learn to say, "SAT tests have a high _g_ loading"), does it follow that one's _g_ is partly determined by one's birth order and/or age difference of one's siblings?

Intelligence appears to have at least some negative correlation with parity.

What have US intelligence psychometricians found here?

Would you expect psychometricians from New Zealand, England, Canada, and Germany to arrive at different findings?

What have non-intelligence US psychometricians found (e.g. wrt personality, aptitudes, interests)?

Who are these people? Can you name a few of the better known ones?

 

[Mandrake]

Do all adults age at the same rate (wrt _g_)?

Quick answer: "no."
Intelligence declines at different rates, causing a significant divergence among people who were once peers. Also, intellectual strengths decline at different rates. Some begin to decline early in life, while others (such as verbal abilities) increase until relatively late in life. You seldom find old people making the kinds of scientific discoveries that earn Nobel Prizes in physics. The value of h^2 increases throughout most of life. If you look at Catell's theory, you will see differences in fluid and crystallized intelligence measures. These are basically second order factors (from factor analysis).

The expert in the study of the study of the psychology of Aging is Timothy Salthouse. He has published several papers in Intelligence that deal with age-related variance. The most general finding is the obvious one that people slow down as they age, thereby making direct comparisons of various studies impractical, when the test subjects are not selected from the same age group. The decline in RT/IT measurements has been independently verified to be substantially caused by a slowing of cognitive processing (as opposed to sensory factors).[*] “Salthouse predicted that the correlation between age and IQ should virtually disappear if mental speed was partialled out. … the correlation between age and RAPM was - .28. After partialling out latency, the correlation between age and RAPM was reduced to a not statistically significant -. 10. Again, this generally supports Salthouse’s contention that a decrease in mental speed is responsible for all age-related declines in fluid intelligence.”[*]
* DOUGLAS A. BORS and BERT FORRIN, Age, Speed of Information Processing, Recall, and Fluid Intelligence, Intelligence 20, 229-248 (1995).

 

[nuenke]

Gottfredson is a sociologist.

She is a sociologist who specializes in general intelligence, with regards to intelligence being correlated with school and job performance. That is her area of expertise. Not everyone doing research in intelligence is a psychometrician - there are many areas of specialization. But she is one of the major contributors to the journal INTELLIGENCE and a major contributor to the science of mental ability. The fact that she does this as part of sociology rather than psychology is not germane. The point is, is she active in the field, and is her work supported and complemented by psychometricians. The answer is clearly yes.

On the other hand look at people like Gardner and Sternberg. They continue to be on the fringes trying to draw a line in the sand with regards to the importance of g and its implications for the workforce as well as racial differences. What determines any persons expertise is a history of solid, respected, verifiable research. There is no one litmus test. It is a matter of convincing others in the field that your hypotheses is better than some other hypotheses. As far as I know, no other hypotheses other than Jensenism has withstood the test of time and scientific grounding. The others are all fringe, non-falsifiable, just-so stories.

 

[hitssquad]

Caffeine is the #1 most popular performance enhancing drug in the world

Thanks hitssquad.There are huge 'problems' in sports wrt 'performance-enhancing' drugs.

There are no elite competitive athletes that I am aware of who do not use performance-enhancing drugs. Most performance-enhancing drugs are not barred by sports bodies.

I would expect that for some sports (e.g. fencing, pingpong; motorcar racing?), a drug which could improve either decision time or motor time (or both!) would be of considerable interest.

Caffeine is such a drug (motor time enhancing and also peak explosive strength enhancing and athletic endurance enhancing), and it is interesting enough that virtually all athletes use it to enhance performance.

At the least I would expect that the drug testers in sports would have a list of drugs known to improve RT

On its face, that would seem to be a strange expectation.

when I get time I'll do some googling.

Try PubMed.

What other detailed studies have been done into the effects of drugs on measured _g_?

Try PubMed. I listed a few over at e-l last year. Here is a related e-l message.

What is known about the incidence of genetic mutations which markedly affect RT (in either direction)?

I would not know.

Do all adults age at the same rate (wrt _g_)?

No. g tends to decline commensurately with decline of physical parameters. Some people age more slowly than others. This seems to be largely mediated by their body's relative production levels of antioxidants such as SOD and uric acid.

People can radically increase their rates of mental decline by abusing alcohol and other drugs and exposing themselves to biologically damaging levels of various chemicals. Lack of micronutrient intake, relative to that of same-age peers, will also increase rate of mental decline, as will lack of food-based antioxident (flavonoids, polyphenolics) intake, again relative to that of same-age peers.

Some adults have managed to virtually halt, relative to that of same-age peers, both their mental and physical age-related decline. These persons have adopted comprehensive anti-senescence regimens. Many of these persons refer to themselves as life extensionists.

Persons with lower IQs to begin with tend to be relatively incompetent at preserving their own health. Thus, the present author would expect that persons with lower IQs to begin with would also suffer greater age-related declines in IQ relative to those of same-age peers. See the recent paper by Gottfredson on IQ and relative hygiene competency.

What does research show wrt variations in the decline of _g_ with age, e.g. men vs women,

Females are known to age more slowly than men, physically. Based on that, I would expect that female cognitive decline is generally also retarded.

menopause,

Age-related hormone decline is known to dramatically affect cognitive parameters. Hormone replacement therapy is known to have an opposite dramatic effect on cognitive recovery in older persons. This effect is mainly attributed to myelination, which is known to be largely mediated by the so-called "sex hormones".

those who use their intelligence vs those who don't

Persons with higher IQs in the first place are known to "use their intelligence" more. This would seem to have to be controlled for, and I do not know if any studies have yet been designed to do that.

the 'old oldies' (those who remain in good physical and mental health well into their 70s, 80s, and 90s) vs everyone else?

There has never been a single documented case of any human reaching the age of 70 in good cognitive health. Before the recent life extension revolution, cognitive decimation on the order of several standard deviations was the norm for 70-year-olds. Persons who are relatively, compared with same-age peers, physically and mentally healthy in their senior years are relatively, compared with same-age peers, physically and mentally healthy in their senior years. Maybe you wanted to know if they were also relatively healthier than average when they were younger. Answer: generally, they were.

 

[Mandrake]

Some adults have managed to virtually halt, relative to that of same-age peers, both their mental and physical age-related decline. These persons have adopted comprehensive anti-senescence regimens.

This is recent and related:
http://www.sciencedaily.com/print.php?url=/releases/2003/01/030128080418.htm

Study Is First To Confirm Link Between Exercise And Changes In Brain

CHAMPAIGN, Ill. -- Three key areas of the brain adversely affected by aging show the greatest benefit when a person stays physically fit. The proof, scientists say, is visible in the brain scans of 55 volunteers over age 55.

The Journal of Gerontology study involved well-educated men and women aged 55 to 79. Their fitness ranged from sedentary to very fit, competitive-ready athletes. Fitness was measured by results of one-mile-walking and treadmill stress tests. Three-dimensional scans of the participants' brains were done using MRI equipment at Carle Foundation Hospital in Urbana. Applying voxel-based morphometry, researchers estimated tissue atrophy in a point-by-point fashion in the targeted regions of the brain.

"Interestingly, we found that fitness per se didnÕt have any influence on brain density," said Kramer, a professor of psychology and member of the Beckman Institute for Advanced Science and Technology at Illinois. "It is fitness as it interacts with age that has the positive effects. Older adults show a real decline in brain density in white and gray areas, but fitness actually slows that decline."

The quoted material is just a sample. The article is interesting.

 

[Moonbear]

You seldom find old people making the kinds of scientific discoveries that earn Nobel Prizes in physics.

Sorry to pick nits here, but there are two obvious social reasons I can think of that can easily account for this other than mental decline. 1) Nobel prizes are usually for work that has really made new breakthroughs and advancements. It's hard to show this has happened soon after a discovery is made, but rather requires the test of time to show it holds up to further scrutiny and actually leads to the advances implied at the outset. So, older scientists just don't stay in the game long enough to get to that point if they only make such a great advancement late in career. 2) You don't find too many senior scientists at the bench. They are trapped in administrative roles, so their great ideas are usually passed on to their students to test.

 

[Tigers2B1]

Sorry to pick nits here, but there are two obvious social reasons I can think of that can easily account for this other than mental decline. 1) Nobel prizes are usually for work that has really made new breakthroughs and advancements. It's hard to show this has happened soon after a discovery is made, but rather requires the test of time to show it holds up to further scrutiny and actually leads to the advances implied at the outset. So, older scientists just don't stay in the game long enough to get to that point if they only make such a great advancement late in career. 2) You don't find too many senior scientists at the bench. They are trapped in administrative roles, so their great ideas are usually passed on to their students to test.

Your #1 doesn't make sense to me, even if true. #2, IF true, begs the question - why?

 

[Moonbear]

Your #1 doesn't make sense to me, even if true. #2, IF true, begs the question - why?

Not sure what about #1 doesn't make sense, so can't clarify.
Re: #2. It's just the way university culture works. Even if someone is a fantastic bench scientist, there are ever increasing pressures to take on administrative responsibility. It starts out small when you're early in your career...you have to serve on some committees to get tenure...then it increases from there...chair a committee, or two, take on the role of journal editor, then editor-in-chief (afterall, journals want those experts running the show), first you review grants, then you chair the study section...it's rather endless. Others are promoted to be graduate program directors or department chairs. It's a strange contradiction in the way universities run...the better you are at doing research, the more they seem to want to pull you away from it by giving you other administrative roles.

 

[Nereid]

Not sure what about #1 doesn't make sense, so can't clarify.
Re: #2. It's just the way university culture works. Even if someone is a fantastic bench scientist, there are ever increasing pressures to take on administrative responsibility. It starts out small when you're early in your career...you have to serve on some committees to get tenure...then it increases from there...chair a committee, or two, take on the role of journal editor, then editor-in-chief (afterall, journals want those experts running the show), first you review grants, then you chair the study section...it's rather endless. Others are promoted to be graduate program directors or department chairs. It's a strange contradiction in the way universities run...the better you are at doing research, the more they seem to want to pull you away from it by giving you other administrative roles.

It sure would be very interesting to see a decent sociological study alone these lines! In the meantime, we can (I'm sure) all give anecodotes. One of my favourites is John Bahcall, who played an extraordinarily important role in neutrino research in the last ~40 years, esp in the astrophysical arena. His capabilities got him dragged into all manner of committees, panels, etc; an example of the latest being on what to do about the Hubble Space Telescope. Amazing as it might seem, he still seems to find time to do really first rate research (although I suspect he outlines the program to bright students, and just checks in whenever he can; the 'bench work' is done by others). An recent example: a superlative paper on observations on the variation in alpha (the fine structure constant) over cosmological time; his finding? no change, within the limits of the observations. Why superlative? Because he found a method to do a test which automatically eliminated so many of the 'other factors' which plagued other efforts before his study.

 

[Mandrake]

There seem to be a few (hopefully not more) participants here who either do not understand or do not believe the science that has shown the strong heritability of intelligence. I just read an interesting interview with the fameous psychometrician Raymond Cattelle. Here is a comment from the interview:

Interview With Raymond B. Cattell
Originally published in The Eugenics Bulletin, Spring-Summer 1984

Raymond B. Cattell obtained his Ph.D. and D.Sc. at London University, where he worked with Spearman developing the theory of intelligence measurement. He has since taught at Harvard and has been for 30 years Distinguished Research Professor at the University of Illinois. His research publications cover 80 books and over 400 articles. His latest book is The Inheritance of Personality and Ability, which has been hailed for its methodological breakthroughs.

How do you think the irrational opposition to the idea of genetic influences on human behavior cane into being, and why does it persist?

CATTELL: One might suppose that all one had to do to overcome this opposition was to point to striking research in behavior genetics. But this research has been around for some time, and still the opposition persists. For example, there are five successive studies of criminal behavior cited in my 1982 book. They show that if a man in prison has an identical twin, it's likely his cotwin will also be in prison. If the twin is fraternal [with 50 percent shared genes, on the average], the likelihood is not nearly as great that he'll be in prison, too, but it's greater than chance. How could one possibly account for this difference with environmentalist explanations? The strong genetic component in criminality has already been proven up to the hilt.

The role of genetics in personality and intelligence has been extensively demonstrated in the last 30 or 40 years. The information is available in numerous textbooks. In almost all traits an appreciable genetic influence exists, varying from 70-80 percent in the case of intelligence, to about 20 percent in the case of superego.

Now, the question is: why aren't these facts known to the American people? Why have academe and the media withheld this information? In Britain, when I was growing up in the '20's, it was common sense to place considerable importance upon heredity in choosing a person to marry, in choosing the occupation for which one was suited, and so on. I was astonished when I came to America to find that eugenics was almost a bad word. One may trace this situation to the sociologists, to Boas and others, and to pressure from minority groups who oppose anything aristocratic.

I think there is a problem widespread in certain societies, notably in America, which consists of the denial, for political or other reasons, of the influence of genetics on human behavior. Of course, the Declaration of Independence has written in it Jefferson's and Franklin's statement that "all men are created equal." Now, neither of those men could possibly have believed that literally, as their other writings amply attest. But to my amazement, I find that two out of three people I ask take that statement to mean that they're genetically equal. The ideal of equality of opportunity has been distorted to mean biological equality. Roger Williams has written a telling little book [Free and Unequal, by Roger J. Williams, 1953; Liberty Press, Indianapolis] about inequality and freedom. He points out that the French Revolutionary trio of ideals of "Liberty, Equality, Fraternity" is internally inconsistent--a society can't have both liberty and equality. Given that people are born unequal in their innate abilities, the only way for a government to bring about equality is by coercion, but ultimately it's futile.

There may also be deeper, unconscious sources of opposition to any form of biological determinism. For example, the individual may feel that heredity somehow restrains him, so he will prefer to deny its influence. But obviously the only reasonable way to deal with nature is to accommodate to its laws, as we do to the law of gravity. If one refuses to acknowledge the importance of gravity and blithely jumps off a cliff, one will find himself in serious trouble. Our society may be jumping off a cliff, so to speak, with regard to its denial of the role of genetics in human behavior.

 

[Mandrake]

The research quoted by both Moonbear and Mandrake seem to show that 'intelligence' isn't particularly well localised in the brain.

That seems to be the implication of the latest information. We are at the beginning, not the end, of the resolution of how and where the brain processes thoughts.

Further, the sex differences would seem to suggest that brain volume, in whole or in part, should not correlate with intelligence.

Lynn has convincingly demonstrated that the mean IQ for women is 4 points below the mean for men. This difference is entirely due to group factors and as such does not conflict with Jensen's frequently reported finding that there is no difference in the mean _g_ for men and women. The primary group factors at work are presumably spatial and quantitative.

- just as skin colour is an adaptation to UV, so aspects of head size and shape are adaptations to local climates - e.g. arctic vs tropical (so, naively, you might expect that any IQ differences would correlate with climate adaptation, if only weakly)

Evolutionary adaptations are going to be driven by advantages in the existing environment that contribute to increased probability that the holders of the genetic allele will survive to reproduce and that their children will do the same. If the existing climate does not contribute to that result, why would you expect an adaptation? Lynn has argued that it was extreme climate that caused increased spatial performance in Mongoloids (contributing to a slight IQ advantage relative to Caucasoids). He also speculated that this spatial advantage may have come at the price of decreased verbal abilities (both differences are measurable).

- the prefrontal cortex comprises ~12.5% of human brains, and ~10.6% of baboon brains. If the brain volume variations claimed by Rushton are due purely to IQ, which is found only in the prefrontal cortex, ...

At present, the evidence points to IQ contributions in various parts of the brain, not just the prefrontal cortex. There was a strong hint of this in earlier research. That research involved the destruction of 48 locations of rat brains (there were meticulous control groups, pairs, etc.), followed by measurements of _G_ (upper case is used to designate the general factor in animals). The total findings are quite revealing and are reported on page 165 of The _g_ Factor. I am uninclined to type the whole result. Part: "Probably the most important finding is the very high correlation between the various tasks' _G_ loading and the number of brain structures that are significantly involved in the task performance -- a rank-order correlation of _.91."

Heavily loaded task = 17 brain structures
Simple task + 4 brain structures

"The _G_ factor correlated -.45 with the presence of _any_ brain lesion."

Britt Anderson determined that the _G_ factor scores for rats correlates with brain weight (they killed the unfortunate rodents) at r= +.48.

The subject of brain size has drawn a great deal of research attention for a very long time. I searched the INTELLIGENCE database and found 21 hits on "brain size." Some of the papers are very interesting, but way to long to discuss as part of this post. Since anyone seriously interested in psychometrics will have (and will have read) a copy of The _g_ Factor, they can review Jensen's comments through the entire chapter titled "Causal Hypothesis." Jensen goes through the math on page 442 to show that measurement data suggest that about 6 points of the W-B IQ gap are due to differences in brain volume. In comparing Negroid, Caucasoid, and Mongoloid means, he says "The regression of median IQ on mean cranial capacity is almost perfectly linear, with a Pearson r= +.998." After giving reasons, he goes on to say "Thus it appears that the central tendency of IQ for different populations is quite accurately predicted by the central tendency of each population's cranial capacity."

The same chapter includes a through discussion of the male-female difference.

The cranial capacity vs. IQ effect is found both within families and between families (P. 441) Jensen says that this implies that the relationship is intrinsic.

 

[NoahAfrican]

I do not think that anyone here is denying the genetics in inherited and thus passes traits to offspring. Eugenics, or whatever, is not at issue here. The issue is in your failure to prove racial differences in testing is rooted in genetics.

Presenting very well educated individuals, who perform studies, is not PROOF of anything. It is simply a BELIEF in them. As I said, if a priest can molest a child, then surly a scientist can bring prejudice into his work. Scientist are not GODS, they are human and subject to emotions and biases.

As I stated before, if an individual has no means of verifying a supposed truth or fact, how does one then choose which ones to believe, from an always variable array of options? Also, how does one then prevent their own biases from determining which thesis is true?

Mandrak and his array of googled authors means nothing and proves nothing. I can tell you that I am 7 foot tall…how could you confirm or deny this? How can any of you prove or disprove it? How can any of you prove or disprove the studies? YOU CANT….all you can do is PICK what you want to believe…because you have know way of knowing and you choice will be biased toward supporting your preconceived notions.

Jensen said..., jensen said...jensen said...jensen said...jensen said...

Is jenson the Son of God or maybe Jensen is God all mighty...the most high...

All hail Jensen...

WHere does Jensen live...I need to get my directions right so I can know which directions to pray...when I pay homage to his rightousness.

 

[iansmith]

They show that if a man in prison has an identical twin, it's likely his cotwin will also be in prison. If the twin is fraternal [with 50 percent shared genes, on the average], the likelihood is not nearly as great that he'll be in prison, too, but it's greater than chance. How could one possibly account for this difference with environmentalist explanations? The strong genetic component in criminality has already been proven up to the hilt.

The problem here is that the example does not prove that there is genetic link. The environment could be in question. Two twin brother in prison. Both grew in the same environment. Was the parents, other relatives in prison?

A better example would be the following.

In my familly, there seems to be high percentage of individual on paternal side with great intellectual capacity. First, 5/8 of my uncle/aunt had not problem learning at school and can do high intellectual work with few effort and 10/15 indiviuals of following generation and 2/3 of the third generation have the same abilities. This lead to suggest that a gene may be responsible for the this intellectual abilities but firts, you have to factor in the environment. The first generation grew up in a working class in the 1960's. This is not environment that promote great intecllectual and the proof stand in the fact that none of the first generation have bachelors degree as their first diploma. They all have technical or no college degree. Very few individuals of the second generation grew up in the same city but they are all from middle class. Already the socio-economic status has increase and 3 of the most gifted have Bachelors. Some of the most gifted have no college diploma, even after several attemps. The third generation lives have the same socio-economic status as their parents, however they are too young to be assess in terms of their academic stating but their learning curve is rapid.

Look at this, it suggest that the intellectual ability of this family is inherited. It can only be stated because three generation were assess for the socio-econmoic status and I look at the whole generation not only at a few individuals. To prove that the heridity exist, you have to compare the gifted against the average individuals at the genetic level. Heredity can only be proven if there is genes associated with it. Once you have what you think is responsible then you have to compare it with other families with suspected heretable gifts.

None of the research stated looked at the genetic level of the heredity. Therefore, most studies, at best, suggest that inheritance should be look at as a factor.

 

[hitssquad]

Fraternal twins function as controls for identical twins

They show that if a man in prison has an identical twin, it's likely his cotwin will also be in prison. If the twin is fraternal [with 50 percent shared genes, on the average], the likelihood is not nearly as great that he'll be in prison, too

The problem here is that the example does not prove that there is genetic link. The environment could be in question. Two twin brother in prison. Both grew in the same environment. Was the parents, other relatives

Ian, the fraternal twins are other relatives. Fraternal twins are both not as genetically related as identical twins, and — unless adopted away — raised in the same environment (except the microenvironment of the home; see Jensen 1998 regarding home microenvironments).

• The macroenvironmental variables responsible for the transient between-families variance in g would therefore seem to be an unlikely source of the observed population difference in g. A more likely source is the microenvironment that produces the within-family variance. The macroenvironment consists of those aspects of interpersonal behavior, values, customs, preferences, and life-style to which children are exposed at home and which clearly differ between families and ethnic groups in American society. The microenvironment consists of a great many small, often random, events that take place in the course of prenatal and postnatal life. Singly they have small effects on mental development, but in the aggregate they may have a large cumulative effect on the individual. These microenvironmental effects probably account for most of the nongenetic variance in IQ that remains after childhood. [79]
  
  79. The theory and empirical evidence for the microenvironmental component of IQ variance are spelled out in Jensen, 1997a.
  
  Jensen A. R. ( 1997a). "The puzzle of nongenetic variance". In R. J. Sternberg & E. L. Grigorenko (Eds.) Intelligence, heredity and environment (pp. 42-88). Cambridge: Cambridge University Press.

(Arthur Jensen. The g Factor. 1998. pp489, 527, 614.)

 

[iansmith]

Ian, the fraternal twins are other relatives. Fraternal twins are both not as genetically related as identical twins, and — unless adopted away — raised in the same environment (except the microenvironment of the home; see Jensen 1998 regarding home microenvironments).

What I meant was that you need more than 2 brothers to really look a heredity? Two brother does point necessarly to heridity. You need other relative such as cousin, uncle, aunts, grand-parents, etc.

 

[Mandrake]

Originally Posted by Mandrake
They show that if a man in prison has an identical twin, it's likely his cotwin will also be in prison. If the twin is fraternal [with 50 percent shared genes, on the average], the likelihood is not nearly as great that he'll be in prison, too, but it's greater than chance. How could one possibly account for this difference with environmentalist explanations? The strong genetic component in criminality has already been proven up to the hilt.
Iansmith: The problem here is that the example does not prove that there is genetic link. The environment could be in question. Two twin brother in prison. Both grew in the same environment. Was the parents, other relatives in prison?

I assume you understand that Cattell's example was intended to be understood as a statistical and not an anecdotal observation. When Cattell stated "The strong genetic component in criminality has already been proven up to the hilt," he was not implying that he had based that conclusion on a single observation, nor even on a set of personal observations. He was telling us that the subject has been reported in many sources and that the results are in agreement. Likewise, your family example, while interesting, is anecdotal.

The relationship of crime to IQ is also interesting. Cattell was not commenting on this, but it is discussed in The Bell Curve, in the chapter titled "Crime." [chapter 11] The discussion points out that criminal behavior correlates negatively with IQ. It should be noted that the content of chapters 1-12 in The Bell Curve are based entirely on a single population group (non-Latino whites).

To prove that the heredity exist, you have to compare the gifted against the average individuals at the genetic level.

The heritability of intelligence can be firmly established without examining ANY gifted individuals. Intelligence is heritable at all IQ levels. The mechanism for describing the heritability of intelligence is to find the mean for the parents and to locate the regression point between that mean and the population group mean. That point then becomes the mean value for the normal distribution that applies to the children of the parents in question.

Heredity can only be proven if there is genes associated with it.

This field of study is particularly associated with researcher Robert Plomin, who discovered IGF2R on chromosome 6. Whether or not the specific genes have been identified, heritability of a trait can be established. The concept of heredity was known long before genetic research identified any trait specific genes.

As for the heritability of intelligence, it is quantified by path analysis and by MZA studies. The data typically fall around h^2 = 72% for young adults, increasing to 80% for old adults. [These are variances, not r values.] Inbreeding depression studies show that intelligence behaves similarly to other traits that are depressed by inbreeding. The only explanation for this is a genetic cause. This one observation is so strong that it cannot be refuted by any amount of hand waving.

The other part of h^2 is the environmental component. This component has been studied in great detail for decades, including the conduct of costly and lengthy experiments. Adoption studies (including interracial ones) have shown that adopted children initially show some correlation to the mean IQs of their adoptive parents, but that this vanishes by late adolescence. As adults they resemble the IQs of their biological parents to approximately the same extent as do children who were reared by their biological parents. Adopted children have a tiny negative correlation to their adoptive siblings.

In adoption studies, such as the Texas Adoption Study (Loehlin, 1989), the IQ correlations between the biological mother (.26) and the adoptive mother (.05) show little evidence of environmental influence by teen years. Virtually all traces of environmental influence are gone (four adoption studies cited by Brand) by adulthood.

Intervention programs have attempted to alter the environmental component, but they have demonstrated that such efforts are doomed to failure. The final conclusion is obvious. Intelligence is determined genetically.

Once you have what you think is responsible then you have to compare it with other families with suspected heritable gifts.

Giftedness is not a requirement for h^2. Dumb people inherit their intelligence, just as do normal and bright people.

None of the research stated looked at the genetic level of the heredity.

I don't think your comment is accurate. You have made an assertion, but it is in disagreement with reality. Although some genes do not express themselves immediately, there is a strong early indication of the correlation between IQ and performance.
The _g_ Factor: General Intelligence and Its Implications:
"IQ rises in predictive value relative to other measures as years go on" (p.77). In a long-term follow-up of a random sample of state-school five-year-olds on the Isle of Wight, IQ correlated strongly (at .50) with children's later educational attainments, when they were fifteen. Such prediction for individuals across ten supposedly formative years is unparalleled in social science."

 

[Evo]

Heredity can only be proven if there is genes associated with it.

This field of study is particularly associated with researcher Robert Plomin, who discovered IGF2R on chromosome 6. Whether or not the specific genes have been identified, heritability of a trait can be established. The concept of heredity was known long before genetic research identified any trait specific genes.

Plomin never succeeded, to date specific genes have not been identified, he gave up his research in this field.

 

[Moonbear]

In adoption studies, such as the Texas Adoption Study (Loehlin, 1989), the IQ correlations between the biological mother (.26) and the adoptive mother (.05) show little evidence of environmental influence by teen years. Virtually all traces of environmental influence are gone (four adoption studies cited by Brand) by adulthood.

And in 1989, the effect of maternal stress on the developing fetus were only beginning to be appreciated and not widely publicized yet. At the time, the majority of work on maternal-fetal interactions of that sort were focusing on alcohol consumption and smoking. I feel like I'm talking to the wall here. There are non-genetic reasons why offspring may be influenced by their birth mother that would affect behavior and/or intelligence. This is the major oversight in the twin and adoptive studies. Or, really, just that most of those studies were done before this interaction was understood. The conclusions may have made sense at the time those studies were done, but they have not withstood the test of time.



One more example:

Early Hum Dev. 2003 Nov;74(2):139-51.
Prenatal maternal cortisol levels and infant behavior during the first 5 months.
de Weerth C, van Hees Y, Buitelaar JK.

BACKGROUND AND AIMS: Research on both animals and humans is providing more and more evidence that prenatal factors can have long-term effects on development. Most human studies have examined the effects of prenatal stress on birth outcome (i.e. shorter pregnancies, smaller infants). The few studies that have looked at the infants' later development have found prenatal stress to be related to more difficult temperament, behavioral/emotional problems and poorer motor/cognitive development. In this paper, we have examined links between late pregnancy cortisol levels and infant behavior during the first 5 months of life. STUDY DESIGN AND SUBJECTS: Seventeen mothers and their healthy, full-term infants participated in this prospective, longitudinal study. The mothers' cortisol was determined in late pregnancy. The infants' behavior was videotaped during a series of bath sessions at the home: at 1, 3, 5, 7, 18 and 20 weeks of age. The mothers filled in temperament questionnaires (ICQ) in postnatal weeks 7 and 18. RESULTS AND CONCLUSIONS: The infants were divided into two groups based on their mothers' late pregnancy cortisol values: high and low prenatal cortisol groups. A trend was found for the high cortisol infants to be delivered earlier than the low cortisol group. Furthermore, the behavioral observations showed the higher prenatal cortisol group to display more crying, fussing and negative facial expressions. Supporting these findings, maternal reports on temperament also showed these infants to have more difficult behavior: they had higher scores on emotion and activity. The differences between the infants were strongest at the youngest ages (weeks 1-7).

PMID: 14580753 [PubMed - indexed for MEDLINE]

 

[iansmith]

The heritability of intelligence can be firmly established without examining ANY gifted individuals. Intelligence is heritable at all IQ levels. The mechanism for describing the heritability of intelligence is to find the mean for the parents and to locate the regression point between that mean and the population group mean. That point then becomes the mean value for the normal distribution that applies to the children of the parents in question.

Rather than using the entire distribution as in QTL studies of other personality traits (Benjamin et al., 2002), the IQ QTL Project selected very high-functioning individuals in order to increase power to detect QTLs of small effect size. Its goal is not to find genes for genius but rather to use very high-functioning individuals in order to identify QTLs that operate throughout the entire distribution, including the low (MMR) end of the ability distribution. This approach is based on the simple hypothesis that, although anyone of many genes can disrupt normal development, very high functioning requires most of the positive alleles and few of the negative alleles. This is just a hypothesis, but one that can be tested when QTLs are found because it predicts that QTLs found for high ability will have a similar effect throughout the rest of the distribution including the low end of the distribution.

This field of study is particularly associated with researcher Robert Plomin, who discovered IGF2R on chromosome 6. Whether or not the specific genes have been identified, heritability of a trait can be established. The concept of heredity was known long before genetic research identified any trait specific genes.

...
I don't think your comment is accurate. You have made an assertion, but it is in disagreement with reality. Although some genes do not express themselves immediately, there is a strong early indication of the correlation between IQ and performance.
The _g_ Factor: General Intelligence and Its Implications:
"IQ rises in predictive value relative to other measures as years go on" (p.77). In a long-term follow-up of a random sample of state-school five-year-olds on the Isle of Wight, IQ correlated strongly (at .50) with children's later educational attainments, when they were fifteen. Such prediction for individuals across ten supposedly formative years is unparalleled in social science."

There have been no traditional linkage studies of intelligence or other quantitative traits, although, as mentioned earlier, linkage has been successful in leading to the identification of more than 200 rare single-gene syndromes for which mental retardation is a symptom (Zechner et al., 2001).

The earlier survey of 100 markers also included two markers for the catechol-o-methyltransferase gene (COMT) that did not suggest associations (Plomin et al., 1995). The COMT gene has been reported recently to correlate with working memory (Egan et al., 2001), which is highly correlated with intelligence (Deary, 2001).

All quote are from
Intelligence, Genetics, Genes, and Genomics
Robert*Plomin and Frank M.*Spinath
http://content.apa.org/journals/psp/86/1/112.html#c92
http://www.ncbi.nlm.nih.gov/entrez/...ve&db=pubmed&dopt=Abstract&list_uids=14717631

 

[Evo]

In adoption studies, such as the Texas Adoption Study (Loehlin, 1989), the IQ correlations between the biological mother (.26) and the adoptive mother (.05) show little evidence of environmental influence by teen years. Virtually all traces of environmental influence are gone (four adoption studies cited by Brand) by adulthood.

Intervention programs have attempted to alter the environmental component, but they have demonstrated that such efforts are doomed to failure. The final conclusion is obvious. Intelligence is determined genetically.

As Moonbear pointed out, your information is outdated and newer studies have proven just the opposite.

The recent study by Turkheimer of the interaction among genes, environment and IQ finds that the influence of genes on intelligence is dependent on class and that environmental factors -- not genetic deficits -- explain IQ differences among poor minorities.

The study was published in the November 2003 issue of the journal Psychological Science. Here is the abstract.

Scores on the Wechsler Intelligence Scale for Children were analyzed in a sample of 7 year old twins from the National Collaborative Perinatal Project. A substantial proportion of the twins were raised in families living near or below the poverty level. Biometric analyses were conducted using models allowing for components attributable to the additive effects of genotype, shared environment, and non-shared environment to interact with socioeconomic status (SES) measured as a continuous variable. Results demonstrate that the proportions of IQ variance attributable to genes and environment vary nonlinearly with SES. The models suggest that in impoverished families, 60% of the variance in IQ is accounted for by the shared environment, and the contribution of genes is close to zero; in affluent families, the result is almost exactly the reverse.

Here is a link to the study. http://www.people.virginia.edu/~ent3c/papers2/Turkheimer psychological science.pdf

 

[nuenke]

The recent study by Turkheimer of the interaction among genes, environment and IQ finds that the influence of genes on intelligence is dependent on class and that environmental factors -- not genetic deficits -- explain IQ differences among poor minorities.

It is well known that intelligence is more malleable in children, and more genetic in adults. Any study that does not test the children later on in life is quite meaningless with regards to intelligence in adulthood. We all know, including the Jensenists, that there is a great deal of environmental influence on children's IQ, but it fades as they grow up.

Frankly, there has not been a coherent alternative to Jensenism. Every attempt to link adult intelligence to environmental causes, except a small percentage of IQ varaince, has failed over and over again. The environmental causation of intelligence is not only unsubstantiated, it has yet to put forth a verifiable, and testable hypothesis as to how it occurs. There are too many theories, all too complex, when the genetic one is the most parsimonious and long-standing theory of individual and racial differences in intelligence.

 

[Evo]

Every attempt to link adult intelligence to environmental causes, except a small percentage of IQ varaince, has failed over and over again.

That would concur with what Turkheimer is saying, no previous studies were done on impoverished children, which is where the difference is.

Please post the peer reviewed studies that followed impoverished children that were then given proper care, nutrition and placed in higher SES homes and showed improved IQs as a result that were then tested as adults and showed a decline in IQ. I haven't seen any.

 

[Mandrake]

Originally Posted by Mandrake
In adoption studies, such as the Texas Adoption Study (Loehlin, 1989), the IQ correlations between the biological mother (.26) and the adoptive mother (.05) show little evidence of environmental influence by teen years. Virtually all traces of environmental influence are gone (four adoption studies cited by Brand) by adulthood.

Intervention programs have attempted to alter the environmental component, but they have demonstrated that such efforts are doomed to failure. The final conclusion is obvious. Intelligence is determined genetically.

As Moonbear pointed out, your information is outdated and newer studies have proven just the opposite.

The recent study by Turkheimer of the interaction among genes, environment and IQ finds that the influence of genes on intelligence is dependent on class and that environmental factors -- not genetic deficits -- explain IQ differences among poor minorities.

I noticed that you presented the Turkheimer paper before and even hounded one participant here about it. The problem is that you don't appear to understand what it does and does not demonstrate. Turkheimer does not present any data for cohorts beyond the age of 7. Intervention studies and adoption studies have consistently found environmental influences that cause IQ in the subjects to improve relative to their peers in childhood. The heritability of IQ in the range Turkheimer studied is typically reported as .40. The gains at age 7 seen by adoption led Scarr to reach the conclusion that she had predicted in advance of her research -- that the adopted children would see a boost in intelligence. But Scarr acted as a responsible scientist and evaluated the same adoptees when they reached the age of 17. She found no residual gains. She and Weinberg concluded that within the range of "humane environments," variations in family socioeconomic characteristics and in
child-rearing practices have little or no effect on IQ measured in adolescence. They claim that most "humane environments" are functionally equivalent for mental development.

Among the things that you should have told us, but didn't:
1 - That the study included only young children and does not make any attempt to extrapolate that all other findings of significant increases in h^2 by age 17 are in any way invalid.
2 - That Turkheimer began his paper by recognizing that the heritability of cognitive ability in childhood is well established.
3 - That Turkheimer made no attempt whatsoever to determine what components of SES he was measuring. There are three obvious items to consider: macro environmental, micro environmental, and genetic. All work to date indicates that the first of these can be found in children, but that it is absent in late adolescents; that by late adolescence, all of the environmental component is of the second type; and that genetic intelligence is the largest determinant of SES.
4 - That Turkheimer says that the effect he observed was related to the homes in which the children were raised. This is interesting, since it relates to the adoption studies which show that after childhood there is no correlation between biologically unrelated children who were reared together in the same home.
5 - That Turkheimer discusses in some detail that SES is not strictly an environmental variable, since it is known to be (statistically) caused by the intelligence of the parents. He points out that the models he used "cannot determine which aspect of SES is responsible for the interactions" observed.
6 - You wrote: "The recent study by Turkheimer of the interaction among genes, environment and IQ finds that the influence of genes on intelligence is dependent on class and that environmental factors -- not genetic deficits -- explain IQ differences among poor minorities." I dispute that his paper says any such thing. His discussion was strictly based on SES and did not single out "poor minorities." The children he studied were listed as white, black, and "other." I believe your comment is a misrepresentation.

The bottom line is that you have attempted (in prior threads) to use this study as a club, while apparently not understanding it. There is nothing in this study that contradicts the items I have presented in this forum.

 

[Mandrake]

Shared environment

Related to the discussion of children, as having a different envrionmental component to the phenotype:

Genetics and intelligence: What's new?
Intelligence, Volume 24, Issue 1, January-February 1997, Pages 53-77
Robert Plomin and Stephen A. Petrill

In this paper, the shared environment variance is given as 25% in childhood and zero after adloscence.

 

[Mandrake]

Originally Posted by Mandrake
In adoption studies, such as the Texas Adoption Study (Loehlin, 1989), the IQ correlations between the biological mother (.26) and the adoptive mother (.05) show little evidence of environmental influence by teen years. Virtually all traces of environmental influence are gone (four adoption studies cited by Brand) by adulthood.

And in 1989, the effect of maternal stress on the developing fetus were only beginning to be appreciated and not widely publicized yet. At the time, the majority of work on maternal-fetal interactions of that sort were focusing on alcohol consumption and smoking.

Conditions in the intrauterine environment have been known as a micro environmental factor for a very long time. There has not been any denial that various such conditions can adversely affect intelligence. This component, combined with whatever other micro environmental components the individual faces does not cause the entire body of statistics relating to heritability to change. The IQ gap between blacks and all other population groups has been measured for the past century and has remained reasonably constant. It remains even when the blacks in question come from the highest SES decile.

I feel like I'm talking to the wall here.

I suspect that you are talking to yourself and you have convinced your audience that you understand the subject much better than one would conclude by reading the above comments. You have not shown any linkage between maternal stress and the Texas Adoption Study, or any of the numerous other similar studies that gave similar results. Instead, you are asserting that those studies were done by incompetent people and that the results were tainted. I see no evidence that the link you want to see is real.

There are non-genetic reasons why offspring may be influenced by their birth mother that would affect behavior and/or intelligence.

Yes. I agree. Jensen has commented that the majority of environmental factors are those that decrease intelligence. When someone gives a value of h^2 as 72%, what do you think accounts for the remaining 28%?

This is the major oversight in the twin and adoptive studies.

That assertion covers a huge amount of ground. It assumes that twin studies contain stresses that were not reported. So, if you have a MZA study that reports h^2 at 70 or so percent, what do you conclude? That stress did what? How does maternal stress enter into a MZA study? Does it cause the value of h^2 to increase or decrease and why?

Or, really, just that most of those studies were done before this interaction was understood. The conclusions may have made sense at the time those studies were done, but they have not withstood the test of time.

In what way have they not withstood the test of time? When MZA studies produce h^2 that is virtually identical to the values calculated by path analysis, any error you suggest must have equally affected both methods. Right? I contend that such an argument is outrageous and impossible.

 

[hitssquad]

Robert Plomin's recent SSADH allele research showing IQ effect of 1.5 points

This field of study is particularly associated with researcher Robert Plomin, who discovered IGF2R on chromosome 6.

Plomin never succeeded, to date specific genes have not been identified, he gave up his research in this field.

When did Plomin give up his research in this field?

• Mol Psychiatry. 2004 Jun;9(6):582-6.
  
  A functional polymorphism in the succinate-semialdehyde dehydrogenase (aldehyde dehydrogenase 5 family, member A1) gene is associated with cognitive ability.[/size]
  
  Plomin R, Turic DM, Hill L, Turic DE, Stephens M, Williams J, Owen MJ, O'Donovan MC.
  
  Social Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, De Crespigny Park, Denmark Hill, London, UK.
  
  Succinate-semialdehyde dehydrogenase (SSADH) deficiency is a rare cause of learning disability. We have investigated SSADH to assess its contribution to cognitive ability in the general population in both case-control- and family-based analyses. Sequence analysis of SSADH revealed four changes affecting the encoded protein, only one of which had a minor allele whose frequency is even moderately common. We genotyped this functional polymorphism in 197 high-IQ cases, 201 average-IQ controls and 196 parent high-IQ offspring trios. The minor allele was significantly less frequent in high-IQ cases and was significantly less frequently transmitted by parents to high-IQ subjects than chance expectation. A previous study has shown that the minor allele encodes a lower activity enzyme than the major allele. These data suggest that higher SSADH activity is associated with higher intelligence across the general population. The effect is small, with each allele having an effect size translating to about 1.5 IQ points.
  
  PMID: 14981524
  
  
  
• Behav Genet. http://content.kluweronline.com/article/491329/fulltext.pdf.
  
  Genotyping Pooled DNA on Microarrays: A Systematic Genome Screen of Thousands of SNPs in Large Samples to Detect QTLs for Complex Traits.[/size]
  
  Butcher LM, Meaburn E, Liu L, Fernandes C, Hill L, Al-Chalabi A, Plomin R, Schalkwyk L, Craig IW.
  
  Social,Genetic and Developmental Psychiatry Centre, Box Number P082, Institute of Psychiatry, De Crespigny Park, London, SE5 8AF, UK.
  
  Large samples and systematic screens of thousands of DNA markers are needed to detect quantitative trait loci (QTLs) of small effect size. One approach to conduct systematic genome scans for association is to use microarrays which, although expensive and non-reusable, simultaneously genotype thousands of single-nucleotide polymorphisms (SNPs). This brief report provides proof of principle that groups of pooled DNA (for example cases and controls) can be genotyped reliably on a microarray. DNA was pooled for 105 Caucasian males and genotyped three times on microarrays for more than 10,000 SNPs (Affymetrix GeneChip(R) Mapping 10K Array Xba 131). The average correlation was 0.973 between the allele frequency estimates for the three microarrays using the same DNA pool. The correlation was 0.923 between the average of the three microarray estimates using pooled DNA and individual genotyping estimates for a Caucasian population as provided by Affymetrix (NetAff(x)(TM)). Thus, genotyping pooled DNA on microarrays can provide a systematic and powerful approach for identifying QTL associations for complex traits including behavioral dimensions and disorders.
  
  PMID: 15319578

 

[Evo]

Turkheimer does not present any data for cohorts beyond the age of 7. Intervention studies and adoption studies have consistently found environmental influences that cause IQ in the subjects to improve relative to their peers in childhood. The heritability of IQ in the range Turkheimer studied is typically reported as .40. The gains at age 7 seen by adoption led Scarr to reach the conclusion that she had predicted in advance of her research -- that the adopted children would see a boost in intelligence. But Scarr acted as a responsible scientist and evaluated the same adoptees when they reached the age of 17. She found no residual gains. She and Weinberg concluded that within the range of "humane environments," variations in family socioeconomic characteristics and in
child-rearing practices have little or no effect on IQ measured in adolescence. They claim that most "humane environments" are functionally equivalent for mental development.

His study was not based on Scarr's study, his study was based on this. In the current study, we used data from the National Collaborative Perinatal Project, which included a large national sample of American mothers, who were enrolled into the study during pregnancy (n48,197), and their children (n59,397), who were followed from birth until age 7 (Nichols & Chen, 1981). Participants were recruited from 12 urban hospitals around the country and included a high proportion of racial minorities and impoverished families.

Among the things that you should have told us, but didn't:
1 - That the study included only young children and does not make any attempt to extrapolate that all other findings of significant increases in h^2 by age 17 are in any way invalid.

Wrong, first sentence of the abstract Scores on the Wechsler Intelligence Scale for Children were analyzed in a sample of 7 year old twins from the National Collaborative Perinatal Project. And again, you are referring to a different study.

2 - That Turkheimer began his paper by recognizing that the heritability of cognitive ability in childhood is well established.

Here is what he said - Although the heritability of cognitive ability in childhood is well established (McGue, Bouchard, Iacono, & Lykken, 1993; Plomin, 1999),the magnitude, mechanisms, and implications of the heritability of IQ remain unresolved. You forgot the last half of the sentence?

3 - That Turkheimer made no attempt whatsoever to determine what components of SES he was measuring. There are three obvious items to consider: macro environmental, micro environmental, and genetic. All work to date indicates that the first of these can be found in children, but that it is absent in late adolescents; that by late adolescence, all of the environmental component is of the second type; and that genetic intelligence is the largest determinant of SES.

Turkheimer goes into great detail about his methods. If you read Methods & Discussion you may understand. These findings suggest that a model in which variability in intelligence among children is partitioned into independent components attributable to genes and environments is too simple for the dynamic interaction of genes and real-world environments during development.The relative importance of environmental differences in causing differences in observed intelligence appears to vary with the SES of the homes in which children were raised. SES is a complex variable, however, and the substantive interpretation to be placed on our results depends on an interpretation of what SES actually measures. The most obvious interpretation of SES in this study is that it measured the quality of the environment in which the children were born and raised. Indeed, this is the function for which SES was intended. Under this interpretation, the observed interaction between SES and the biometric components of IQ could be indicative of precisely the kind of nonlinear relationship between rearing environment and intelligence that has been suggested by Scarr (1981) and Jensen (1981), with differences among poor environments contributing more to differences in phenotypic outcome than differences among middle class or better environments contribute. It would be naive, however, to interpret SES strictly as an environmental variable. Most variables traditionally thought of as markers of environmental quality also reflect genetic variability (Plomin & Bergeman, 1991). Children reared in low-SES households, therefore, may differ from more affluent children both environmentally and genetically (Gottesman, 1968), and the models we employed in this study do not allow us to determine which aspect of SES is responsible for the interactions we observed. Indeed, it will be difficult to separate the genetic and environmental aspects of SES or other measures of the family environment in research designs of this kind, because children raised in the same home necessarily have the same SES.

Genetic variability in SES might also introduce a complication to the models themselves. Phenotypic SES and IQ are correlated, and that correlation is potentially mediated both genetically and environmentally. Therefore, the models are attempting to detect an interaction between genotype and environment in the presence of a correlation between genotype and environment, raising the concern that the presence of the correlation might introduce bias into the estimation of the interaction. However, Purcell (2003) has conducted an exhaustive series of simulations that suggest no bias is introduced, as long as the main effect of the moderating variable is included in the model, as we have done here. The presence in the model of the main effect of SES means that the biometric model fitting is actually being conducted on the portion of IQ that is independent of both the genetic and environmental components of SES. (We note, however, that omitting the main effect from the model did not change the results to a significant degree.

4 - That Turkheimer says that the effect he observed was related to the homes in which the children were raised. This is interesting, since it relates to the adoption studies which show that after childhood there is no correlation between biologically unrelated children who were reared together in the same home.

This study is unique in that it is based upon impoverished households, something that has not previously been studied. Why do you keep bringing up earlier unrelated studies that this study supercedes?

5 - That Turkheimer discusses in some detail that SES is not strictly an environmental variable, since it is known to be (statistically) caused by the intelligence of the parents. He points out that the models he used "cannot determine which aspect of SES is responsible for the interactions" observed.

Ah, you did read it.

6 - You wrote: "The recent study by Turkheimer of the interaction among genes, environment and IQ finds that the influence of genes on intelligence is dependent on class and that environmental factors -- not genetic deficits -- explain IQ differences among poor minorities." I dispute that his paper says any such thing. His discussion was strictly based on SES and did not single out "poor minorities." The children he studied were listed as white, black, and "other." I believe your comment is a misrepresentation.

That does not preclude poor minorities.

The bottom line is that you have attempted (in prior threads) to use this study as a club,

What, because it doesn't agree with you? I really think you need to retract that statement as well as the earlier statement you made. Why do you insist on personal attacks?

There is nothing in this study that contradicts the items I have presented in this forum.

It probably contradicts most of what you have posted on this forum.