Questions on _g_ and intelligence

[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.

 

[Evo]

When did Plomin give up his research in this field?

Oh, you're right, I am guilty of not reading that closely and was thinking of Plomin's attempt to identify genes linked to IQ.

 

[Mandrake]

Originally Posted by Mandrake
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.

Evo: His study was not based on Scarr's study, his study was based on this.

I did not claim that his study was based on Scarr's study. I pointed out the important fact that this study was limited to children up to 7 years old. When Scarr did her work, she reached one conclusion when she evacuated her subjects at age 7 and then reversed her conclusion when she tested them again at age 17. Her finding is consistent with all other longitudinal studies in demonstrating that the shared environment component vanishes after age 7 and before age 17.

In the current study, we used data from the National Collaborative Perinatal Project,

Thank you. I have read and understood the paper. Whether or not you have read it, your comments indicate that you do not understand it nor how it fits into the big picture.

Quote:
Originally Posted by Mandrake
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.

Evo: 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.

The study I have read is from Psychological Science, vol. 14, No. 6, Nov. 2003. There is no extrapolation of any finding in that paper to heritability beyond the age of 7. As such, the entire study is of interest only with respect to young children and says nothing about children past the age of 7. All prior research shows that the shared environment component of heritability completely vanishes by age 17.

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

Evo: 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?

I didn't quote the sentence. What part of the material you quoted is significant and derived from the study?

Quote:
Originally Posted by Mandrake
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.

That is not what I challenged. You don't understand what he wrote do you? The material you quoted below is precisely the point of my comment.

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. ... 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.

Quote:
Originally Posted by Mandrake
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 supersedes?

His study does not supersede anything. It is a study that includes low SES people who have produced lower heredity scores than found in other studies, but under circumstances that the researcher cannot separate from pure genetic or mixed genetic factors. He did not suggest that there is any reason to expect the subjects of his study to mature by a different path than all of the other children who have been studied by longitudinal studies.

Quote:
Originally Posted by Mandrake
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.

And, unlike some folks, I understood it.

Quote:
Originally Posted by Mandrake
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.

You don't appear to understand the material. There was no attempt to study poor minorities, nor was there any attempt to separate the cohorts and study them separately. NONE of the data are based on a single "minority" or population group or race.

Quote:
Originally Posted by Mandrake
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?

You badgered bobf with the article (even though you do not show any appreciation of it) on dates that preceded my joining the discussion forum.

I really think you need to retract that statement as well as the earlier statement you made. Why do you insist on personal attacks?

My statement is a simple matter of the record. I have not attacked you personally, I have pointed out the errors in what you have posted.

Quote:
Originally Posted by Mandrake
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.

Really? I don't think so. I challenge you to quote my prior comments and to then demonstrate that the study contradicts them. Good luck.

 

[Evo]

Mandrake, this study is groundbreaking, this population segment has never been studied before in this way, therefore none of your outdated studies are relevant to this. Unless you have some recent studies that are based on the same impoverished level of participants, you don’t have an argument against his study. This is all new. Only time will tell.

I think it is wonderful news that children can be helped, don't you?

As Turkheimer himself concluded - In the fractious history of scientific investigations of the heritability of intelligence, the effects of poverty, and the relations between them, there has been only one contention with which everyone could agree: Additive models of linear and independent contributions of genes and environment to variation in intelligence cannot do justice to the complexity of the development of intelligence in children. Only recently have statistical models and computational capacity advanced to the point that less simplistic models can actually be fit. Although there is much that remains to be understood, our study and the ones that have preceded it have begun to converge on the hypothesis that the developmental forces at work in poor environments are qualitatively different from those at work in adequate ones. Clarification of the nature of these differences promises to be a fascinating, and hopefully unifying, subject for future investigation.

 

[Nereid]

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

How much (range)? How extensively has this been tested?

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

I'm taking this step-by-step, and per hitssquad's Jensen quote, _g_ correlations are most solidly demonstrated in the US.

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

You really threw me with this one! :surprise: Aren't you the psychometrician?

Anyway, here are some (non-intelligence) 'psychometric instruments' that I found by doing some googling:
- 16 PF5 ("Based on Cattell's trait theory of personality, this instrument has been adapted for use within organisations.")
- Myers-Briggs ("Based on Jung's type theory of personality, developed by Isabel Myers and Katherine Briggs.")
- Strong's Career Interest inventory ("based on Holland's typology of activities. The theory agues that individuals differ in the degree to which they have a preference for certain activities and that jobs contain these activities in varying degrees")
- Team Climate Inventory ("developed by Anderson and West (1996) allows objective comparison of the way teams function").

I also found references to DISC ("DISC measures four factors of an individual's behaviour: Dominance, Influence, Steadiness and Compliance. They can be characterised as assertiveness, communication, patience and structure.")

Finally, this university site has a looong list of psychometric tests, of which only a small subset seem to be 'intelligence tests'.

 

[hitssquad]

Did Robert Plomin give up his attempt to identify genes linked to IQ

When did Plomin give up his research in this field?

Oh, you're right, I am guilty of not reading that closely and was thinking of Plomin's attempt to identify genes linked to IQ.

I was also thinking of the attempt by Plomin to identify genes linked to IQ. My link to his current research would seem to belie any speculation that he has given up his IQ-gene research — or are you making distinctions between QTL's, alleles and genes?

Did Robert Plomin give up his attempt to identify genes linked to IQ?

 

[Mandrake]

Oh, you're right, I am guilty of not reading that closely and was thinking of Plomin's attempt to identify genes linked to IQ.

So far, hitsquad seems to be telling you that you have ducked his question.

For the benefit of anyone interested, Jensen: "At least four genes or DNA segments that affect IQ have been identified by behavior geneticist Robert Plomin of the Institute of Psychiatry of the University of London. And his investigation continues." [Miele (2002) - Intelligence, Race, and Genetics: Conversations with Arthur R. Jensen, P. 103]

If your comment is correct, please substantiate it. If it is incorrect, you might want to admit your error more clearly.

 

[Evo]

Did Robert Plomin give up his attempt to identify genes linked to IQ?

According to an article I read and his home page. He's shifted his focus to another study for now. He never published his findings on his studies linking genes to IQ. I believe there are some others that have picked up that research. The link you posted appears to be related to his current research.

From your link - "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."

From his website -

"Plomin is currently conducting a study (TEDS) of all twins born in England during the period 1994 to 1996, focussing on developmental delays in early childhood and their association with behavioural problems."

"The Twins Early Development Study (TEDS) represents Robert Plomin's major current research effort, funded as a programme grant by the UK Medical Research Council. "

http://www.robertplomin.com/

 

[BlackVision]

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.

Well you ducked this question before but might as well try again. What factors did the Turkheimer take into consideration that a higher IQed individual will be more likely to be in higher SES due to the fact that one's IQ level effects one's ability to be in a certain SES level? Rather than the vice versa of SES level effecting IQ. Without taking in such factors, any conclusions by this study will be considered void.

As I've said before, this study is similar to another study showing that college graduates have an IQ of 110. And then trying to claim that going to college effects your IQ. Rather than the more correct answer that it's their IQ that allowed them to go to college. It's using faulty logic and working backwards.

 

[Mandrake]

Originally Posted by Mandrake
Intelligence appears to have at least some negative correlation with parity.

How much (range)? How extensively has this been tested?

I don't know. It is something that I have seen mentioned in various books and papers as part of the discussion of within family variance. Unfortunately, Jensen's books are rather poorly indexed (unlike The Bell Curve) so it is always difficult to find material in them.

Miller says that the levels of testosterone that children are exposed to may be related to parity. Presumably he meant the intrauterine environment.

Searching my files didn't work. The problems involve multiple meanings of the term "parity" and the difficulty in removing "disparity" from the search.

Mandrake: Who are these people? Can you name a few of the better known ones?
Nereid: You really threw me with this one! Aren't you the psychometrician?

I am a physicist with a strong interest in psychometrics. I know the people who deal with intelligence, but that's it. I am familiar with the Myers-Briggs test you listed, but it only relates to intelligence in that intelligent people tend to have a profile that is not common in the general population (INTJ). Adding INTJ and INTP, accounts for 75% of the Mensa level population (per Mensa's report).

 

[Mandrake]

Mandrake, this study is groundbreaking, this population segment has never been studied before in this way, therefore none of your outdated studies are relevant to this.

Your comments on this single study reveal that you do not understand it nor do you understand how it relates to the rest of the literature. If you think any item I have discussed here is outdated as a result of the study (you have said that ALL were), I challenge you (again) to quote my comments and then show how they are now in error. You didn't accept my challenge before and I doubt that you will now. It is quite evident that you have an attitude, but are not appropriately informed to justify that attitude.

I think it is wonderful news that children can be helped, don't you?

The findings of the study were limited to the conclusion that genetic expression may be influenced by SES. The investigators were unable to even sort out genetic from non-genetic factors and said so. What "help" do you think they discussed in their paper? Do you think that they reported any increase in any child due to any aspect of their study?

Your obvious failure to understand this study has caused you to make statements here that are nonsense. You even used your assumed understanding to badger bobf concerning the paper. That strikes me as absolutely amazing!

 

[Evo]

Well you ducked this question before but might as well try again. What factors did the Turkheimer take into consideration that a higher IQed individual will be more likely to be in higher SES due to the fact that one's IQ level effects one's ability to be in a certain SES level? Rather than the vice versa of SES level effecting IQ. Without taking in such factors, any conclusions by this study will be considered void.

He addresses that here - 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.)

 

[hitssquad]

Using Questia as an index for social science texts

Unfortunately, Jensen's books are rather poorly indexed (unlike The Bell Curve) so it is always difficult to find material in them.

Jensen's 1980 book Bias in Mental Testing seems to me to have a good index. But, unfortunately, it is not published on the web. Jensen's 1998 book The g Factor, on the other hand, does have, it seems to me, a poor index, but the fact that Questia (subscription cost at the yearly rate equals 33 cents per day) publishes it on the web makes that somewhat moot since Questia has an in-book search function that even non-subscribers are allowed to use. If you at least own the physical book, you can use the Questia search function as an index to help you find things in the book.

 

[Evo]

Your comments on this single study reveal that you do not understand it nor do you understand how it relates to the rest of the literature. If you think any item I have discussed here is outdated as a result of the study (you have said that ALL were), I challenge you (again) to quote my comments and then show how they are now in error. You didn't accept my challenge before and I doubt that you will now. It is quite evident that you have an attitude, but are not appropriately informed to justify that attitude.

Mandrake you keep quoting form the same old studies that everyone else has. You are the one that comes unglued if someone posts information that you disagree with. Feel free to attck the material I post, you may prove it wrong. You may not, however, attack me personally for posting a conflicting view.

The findings of the study were limited to the conclusion that genetic expression may be influenced by SES. The investigators were unable to even sort out genetic from non-genetic factors and said so. What "help" do you think they discussed in their paper? Do you think that they reported any increase in any child due to any aspect of their study?

The study shows that environment is a substantially significant factor in increased IQ in the children studied and they are continuing this study.

Your obvious failure to understand this study has caused you to make statements here that are nonsense. You even used your assumed understanding to badger bobf concerning the paper. That strikes me as absolutely amazing!

Your opinion means nothing to me Mandrake. No, I was trying to get BV to answer my questions, which he kept "dodging".

 

[Evo]

I am familiar with the Myers-Briggs test you listed, but it only relates to intelligence in that intelligent people tend to have a profile that is not common in the general population (INTJ). Adding INTJ and INTP, accounts for 75% of the Mensa level population (per Mensa's report).

Myers-Briggs and DISC are both personality tests. Every few years at work we are required to take them. I have been both an INTJ and an INTP in Myers Briggs. My DISC test last year I was a D with a High I. The test before that the two were reversed.

 

[Moonbear]

Hitssquad, or whoever first brought up Plomin, that's some interesting work. I read his most recent article (the one in Behavior Genetics) this morning while drinking my coffee (admittedly, skimming through some parts quickly), and found it pretty interesting and solid. I especially liked that he had multiple analyses and what seemed to be a good control, which unfortunately threw a monkey wrench into the works. But at least he addressed it candidly and gave some different possible explanations, which I personally found very satisfying in the way they were discussed. I also liked that he took the reasonable approach of starting out with as homogeneous a study population a possible, with the exception of IQ being either high or average. This seemed to remove a lot of the possible confounds. He managed to address each of the questions/potential criticisms I raised in my own mind as I was reading.

 

[nuenke]

Are you familiar with the book "The Relationship Code: Deciphering Genetic and Social Influences on Adolescent Development" by Reiss, Neiderhiser, Hertherton and Plomin, 2000. It reports on a massive 13 year study funded by NIH, and supports the loss of shared environmental influence on a host of behaviors as children grow, including IQ (they used a proxy). I have excerpts I can email you. I have seen little of this study floating around, perhaps because it is so damaging to the environmentalists.

 

[BlackVision]

No, I was trying to get BV to answer my questions, which he kept "dodging".

Exactly which questions am I "dodging"? What an ironic accusation coming from you.

 

[Moonbear]

Nuenke, I wasn't familiar with it, so just went over to Amazon and looked it up. They had excerpts there, so I read those and the reviews of the book (it's currently out of print). From the excerpts there, it doesn't sound like the authors are saying environmental influences are lost at all. Instead, it seems to be suggesting a fairly reasonable argument that underlying genetic predisposition and environmental factors interact with one another to influence adolescent behavior. From the excerpts there, I can't tell if they are strictly limiting environmental factors to social factors or other non-genetic biological influences, or if those are more likely to wind up lumped in with the genetic factors. Do your excerpts say something different?

 

[Mandrake]

Mandrake you keep quoting form the same old studies that everyone else has.

Unfortunately, you have not been able to understand that (with rare exceptions) I have not been discussing early childhood in my messages. The study which has overwhelmed you deals only with children up to the age of 7. There is nothing in the paper that projects beyond that age. There is considerable material in peer reviewed sources which suggests that all shared environmental components of intelligence vanish after age 7 and before age 17. You have made numerous comments that you apparently think are related to the Turkheimer paper, which are purely figments of your imagination. One, is your comment about "helping" children. That subject was not discussed in the paper. I asked you about it, but you (as usual) ducked my question. You said that all of my prior comments were invalid because of this paper. The fact is that none are invalid because of the paper. For the third time, I challenge you to simply cut and past my comments from this thread (there are plenty) and show how each of them is invalidated by Turkheimer. You can't do it, but it will be fun to watch you try, or to duck it yet again.

The study shows that environment is a substantially significant factor in increased IQ in the children studied and they are continuing this study.

Is I have reminded you before, your comments suggest a lack of understanding. The paper shows only that very low SES (a high proportion of impoverished families) causes a large variance in heritability among very young children. Of the 4 tests that were conducted, two were significantly below the age that testing is considered to be reliable (that age is 3, while tests were done at 8 months and 1 year). The study did not state ANYTHING about the influence of environment for higher than "impoverished" SES.

 

[Mandrake]

Jensen's 1980 book Bias in Mental Testing seems to me to have a good index. But, unfortunately, it is not published on the web.

It is much better than The _g_ Factor.

If you at least own the physical book, you can use the Questia search function as an index to help you find things in the book.

That is a useful service, but one that I do not have. The approach I have taken has been to create my own index. It is labor intensive, but I find the extra work helps me to recall the contents.

 

[Mandrake]

From the excerpts there, it doesn't sound like the authors are saying environmental influences are lost at all. Instead, it seems to be suggesting a fairly reasonable argument that underlying genetic predisposition and environmental factors interact with one another to influence adolescent behavior.

I previously referenced this paper from Intelligence:
Genetics and Intelligence: What’s New?
ROBERT PLOMIN, STEPHEN A. PETRILL
Institute of Psychiatry, London

On page 12, it says:
Until recently, environmental factors that affect intelligence were thought to operate primarily in a shared manner. For example, our earlier review of genetic influences on intelligence concluded that shared environment accounted for about 25% of the variance of IQ scores. The strongest evidence for the importance of shared environment comes from the correlation for adoptive siblings, that is, pairs of genetically unrelated children adopted into the same adoptive families. As shown in Figure 2, adoptive siblings correlate about .30 for IQ, suggesting that about a third of the variance in IQ can be attributed to shared family environment. However, the studies reviewed in Figure 2 happened to assess adoptive siblings as children. In 1978, the first study of older adoptive siblings yielded a strikingly different result: The IQ correlation was -.03 for 84 pairs of adoptive siblings from 16 to 22 years of age (Scat-r & Weinberg, 1978). Other studies of older adoptive siblings have also found similarly low IQ correlations. The most com-pelling evidence comes from a lo-year follow-up study of 181 adoptive siblings. At the average age of 8 years, their IQ correlation was .26. However, 10 years later, their IQ correlation was - .Ol , suggesting that shared family environmental effects on IQ decline to negligible levels after adolescence (Loehlin, Horn, & Willerman, 1989) (see Figure 7).

We are confident that the question is when, not whether, genes will be found that are associated with intelligence. Indeed, many genes have already been found that are associated with low intelligence. More than 100 rare single-gene disor-ders include mental retardation among their symptoms (Walhsten, 1990).
The figure 7 is on page 13 and shows that the shared environment shows up in childhood, then vanishes completely.

 

[Mandrake]

Concordance rates of IQ scores

This may be of interest to some of you:

Concordance rates of IQ scores

Evidence from family studies provides the main supporting evidence from which arguments about the relative roles of genetics and environment are constructed.

A large number of the study of twins reared apart was undertaken by Thomas Bouchard of the University of Minnesota starting in 1979. He “collected” pairs of separated twins from all over the world and reunited them while testing their personalities and IQs. Other studies at the same time concentrated on comparing the IQs of adopted people with those of their adopted parents and their biological parents or their siblings. Put all these studies together, which include the IQ tests of tens of thousands of individuals, and the table looks like this:

• Same person tested twice 87%
  
  Identical twins reared together 86%
  
  Identical twins reared apart 76%
  
  Fraternal twins reared together 55%
  
  Biological siblings reared together 47% (studies show that reared apart about 24%)
  
  Parents and children living together 40%
  
  Parents and children living apart 31%
  
  Adopted children living together 0%
  
  Unrelated people living apart 0%

from
Ridley, M. (1999). Genome: The autobiography of a species in 23 chapters. London: Fourth Estate Ltd.

 

[hitssquad]

The Physics Forums 'Science Expert' medal and its nominators

Let me add that one contributor to these discussions (screen name "hitsquad") is well informed and has posted comments that are identical to what I would have written about the same issues. This person has addressed the questions pertaining to intelligence with facts that are scientifically valid and known to those who have studied the subject in depth.

Go for it. I won't complain.

 

[nuenke]

From the excerpts there, it doesn't sound like the authors are saying environmental influences are lost at all. Instead, it seems to be suggesting a fairly reasonable argument that underlying genetic predisposition and environmental factors interact with one another to influence adolescent behavior.

The book looks at three causes for differences in intelligence and behaviors. Using a very large group, and using longitudinal studies, as well as including all of the relationships (twins, adopted children, families with half brothers/sisters, etc.), they determined that when young, the shared environment may be important, but as children grow older, it is almost exclusively genes and the non-shared environment that determines these factors. That is, the family environment has very little impact on children once they enter their teens - they find, produce and gravitate towards their own individual environments depending on their genes and other unknown factors. That is, no one really knows what the interaction is, but it is not the family that makes the person.

This is pretty much accepted by behavior geneticists. Also see the Nurture Assumption by Judith Rich Harris, 1998. She discovered this, if I remember right, because she edited a lot of research papers and noticed irregularities. Her book is a much easier read, and explains how children find their own niches.

Of course, this new research really hurts educators, psychologists, social workers, etc. There is a huge industry built upon naïve environmentalism, and they are not about to lose their livelihoods because new research has made many of their programs quite meaningless.

 

[Moonbear]

That is, the family environment has very little impact on children once they enter their teens - they find, produce and gravitate towards their own individual environments depending on their genes and other unknown factors. That is, no one really knows what the interaction is, but it is not the family that makes the person.

Can you please expand on this? Are they saying environment is not at all a factor, or that the social influences shift from family to some other source? Part of the social shift in adolescence is becoming independent of your parents and instead identifying more with same-aged peers.

Of course, this new research really hurts educators, psychologists, social workers, etc. There is a huge industry built upon naïve environmentalism, and they are not about to lose their livelihoods because new research has made many of their programs quite meaningless.

You mean those who would say it's ONLY social factors, and NEVER biological? Sure, any view that rigid isn't going to last long in any field of science.

Something that still doesn't seem clear to me is which definitions of environmental are being employed here. I suspect we may not all have the same idea in mind. When I think of environmental influences, I think of anything coming from outside our own body, including physical/chemical/biological external influences (including intrauterine environment of the fetus) as well as social influences from both family and other people (teachers, friends, neighbors). In a number of the posts here, I get the impression environmental is being used synonymously with social influences only, i.e., nature vs nurture. Conversely, I also keep getting the impression that some are considering anything that is not due to social influence must be due to genetic influence rather than other physical/biological factors, and I'm not sure where everyone is categorizing those factors. It is quite possible this is leading to a good deal of our misunderstandings in this thread because we aren't all thinking the same definitions.

In Plomin's 2004 article, he discusses that one of the reasons why it may be difficult to pinpoint a genetic link to IQ is that a single gene may only account for something as small as 1% of the variation, such that you can never detect a difference by looking for one gene at a time. So, for those who are willing to embrace the genetic linkage, and would accept Plomin as an authority on the subject, why could the same not be true of environmental factors? Often, we try to study single environmental factors to avoid the difficulty in interpreting findings with numerous variables. What if we can't detect any differences for a single environmental factor, such as SES, for the same reasons we can't detect significant differences related to a single gene? And if we did find a gene, we'd need to show that it then results in a functional protein that also differs in expression levels. And is that protein expression altered by environment? Or does it alter the way we respond to our environment? Or both, in a feedback loop? There is prior evidence that both can occur. In behavioral endocrinology, hormones influence behavior, but then behavior also influences hormone secretion. It's incredibly difficult to tease these two directions of interaction apart.

 

[hitssquad]

Definitions of heritability and environment and introduction to concept of variance

That is, the family environment has very little impact on children once they enter their teens - they find, produce and gravitate towards their own individual environments depending on their genes and other unknown factors. That is, no one really knows what the interaction is, but it is not the family that makes the person.

Can you please expand on this? Are they saying environment is not at all a factor, or that the social influences shift from family to some other source?

In regards to heritability, we consider phenotypic variance accountable for on the one hand by environemental variance and on the other hand by genetic variance. If a teen "gravitates toward" specific environments, genetics would be accounting for the variance in environment and hence ultimately accounting for variance in phenotype. What is proposed is not that the teens are shifting from the family to random outside influence, but to ouside influence that caters to the teens' biological programming, of which genetics accounts for the bulk of the variance.

Part of the social shift in adolescence is becoming independent of your parents and instead identifying more with same-aged peers.

And what is proposed is that peer selection (among other selections by teens) is not random, but is largely a product of genetically-determined tendency. There is no accounting for taste, as they say, and it is proposed that variance in taste in environment may be more largely accountable for by variance in genetic code than by variance in environment.

Something that still doesn't seem clear to me is which definitions of environmental are being employed here.

Heritability refers to variance in phenotypic outcome accountable for by genetics as opposed to accountable for by environment. Environment is all factors left over when genetic code is controlled for.

When I think of environmental influences, I think of anything coming from outside our own body

Then you are mistaken, because in terms of heritability environment is any factor that is not genetic. That includes the body itself. For example, genetic code expresses throughout a person's life. But the state of the body has visible effects on genetic expression. When people reach physical maturity, their genes still express proteins that code for growth factors. Yet they do not grow any more. This is because of states in the body that prevent growth in the presence of growth factor. One of these states is the hardening of the ends of bones. If the ends of bones remained soft, as they are when we are children, growth factors might continue to stimulate bone growth indefinitely - and people would grow to towering heights throughout their lifetimes, as trees do.

In a number of the posts here, I get the impression environmental is being used synonymously with social influences only, i.e., nature vs nurture.

Yes. This is a classic confusion of the term "environment." What normally happens in nature/nurture discussions is that the equivocation fallacy is committed in regards to the definition fo the term environment. One moment it means all environment (all variance not genetic), and the next moment it means only intellectual stimulation. Arthur Jensen suggested that when we discuss environmental variance we be clear about whether we are speaking in terms of biological variance; variance in intellectual stimulation; or all non-genetic cariance (all environmental variance).

In Plomin's 2004 article, he discusses that one of the reasons why it may be difficult to pinpoint a genetic link to IQ is that a single gene may only account for something as small as 1% of the variation, such that you can never detect a difference by looking for one gene at a time. So, for those who are willing to embrace the genetic linkage, and would accept Plomin as an authority on the subject, why could the same not be true of environmental factors?

There is no environmental counterpart to the discrete gene. In regards to heritability, environment is taken as one big lump and genetics is taken as one big lump. It stands to reason that if it has been established that genetic variance accounts for any amount of variance in a given phenotypic trait that we should also be able to find variance in specific genes that accounts for the same phenotypic trait variance. But searching for genes is not directly a part of heritability studies. Heritability of g in various human populations has already been established by selectively controlling for variance in environment and by selectively controlling for variance in genetic code.

What if we can't detect any differences for a single environmental factor, such as SES, for the same reasons we can't detect significant differences related to a single gene?

SES is not comparable to a discrete gene. You can silence a discrete gene, but you cannot silence SES. SES is an axis. A gene is quantum piece of code.

And if we did find a gene, we'd need to show that it then results in a functional protein that also differs in expression levels.

No. The gene in question might be coding for the silencing or unsilencing of other parts of the genome. Discrete production of a protein by the IQ-related gene in question may not be necessary for that to occur.

And is that protein expression altered by environment?

Of course it is affected by environment. Studies of heritability have nothing to do with teasing out discrete affectors. They simply control for variance of environment and genetics and see how that results in changes in variance of expression of one or more phenotypic traits.

 

[Moonbear]

Then you are mistaken, because in terms of heritability environment is any factor that is not genetic. That includes the body itself. For example, genetic code expresses throughout a person's life. But the state of the body has visible effects on genetic expression. When people reach physical maturity, their genes still express proteins that code for growth factors. Yet they do not grow any more. This is because of states in the body that prevent growth in the presence of growth factor. One of these states is the hardening of the ends of bones. If the ends of bones remained soft, as they are when we are children, growth factors might continue to stimulate bone growth indefinitely - and people would grow to towering heights throughout their lifetimes, as trees do.

I wouldn't have chosen the word mistaken. It appears to be a difference in terminology from my field in which environmental does mean anything from outside the body. This is why I asked, because it is becoming apparent that we aren't all talking about the same thing.

Yes. This is a classic confusion of the term "environment." What normally happens in nature/nurture discussions is that the equivocation fallacy is committed in regards to the definition fo the term environment. One moment it means all environment (all variance not genetic), and the next moment it means only intellectual stimulation. Arthur Jensen suggested that when we discuss environmental variance we be clear about whether we are speaking in terms of biological variance; variance in intellectual stimulation; or all non-genetic cariance (all environmental variance).

Well, at least that much we can agree on. We need to be explicit in our definition of environment, or, more importantly, various authors' definitions of environment, when discussing it here. I think this is leading to a lot of additional confusion in this discussion.

 

[Mandrake]

Of course, this new research really hurts educators, psychologists, social workers, etc. There is a huge industry built upon naïve environmentalism, and they are not about to lose their livelihoods because new research has made many of their programs quite meaningless.

Yes indeed! The political and job related motivations for promulgating false concepts concerning environmental factors is huge. It has resulted in massive spending without returns. We have an inverse relationship between school spending and educational results precisely because the spending has been narrowly focused on population groups that will not show cognitive improvements as a result of the programs advertised to produce gains. The politics of this issue are so robust that I doubt that the subject can be discussed openly in any educational or political forum. The special interest side will simply shout down the scientific findings and use their usual "dirty racist" name calling as their only weapon. This struggle is similar to the Christian church as it sought to stop the advancement of science.

 

[Mandrake]

The Shared Environment

Can you please expand on this? Are they saying environment is not at all a factor, or that the social influences shift from family to some other source?

There are shared and not-shared environmental factors. Family factors are the shared ones. I previously quoted from Plomin (this thread) that the shared factors vanish in adolescence. In childhood, the shared factor is about 25%. From there, it goes to zero.

Part of the social shift in adolescence is becoming independent of your parents and instead identifying more with same-aged peers.

More likely is that genetic expression increases.

When I think of environmental influences, I think of anything coming from outside our own body, including physical/chemical/biological external influences (including intrauterine environment of the fetus) as well as social influences from both family and other people (teachers, friends, neighbors).

Jensen divides environmental factors into macro and micro, where the macro environment is that which is due to social interactions (family, institutional, etc.) and the micro environment is due to chemical and biological elements. The micro environment includes the intrauterine environment. When you subtract the variance due to genetics (considering intelligence), the factors that remain are environment and error. Together they add to about20-30% of the total variance.

Obviously, adoption studies are important to the observation of the evaporation of the shared environmental component.

By adolescence (by which time parental influence is weak in the modern West), unrelated children who have grown up as adoptees in the same family show quite simply no similarity at all in their levels of g . As Neisser et al. (1995) conclude in their review for the American Psychological Association, "Severely deprived, neglectful or abusive environments must have negative effects on a great many aspects of development, including intelligence. Beyond that minimum, however, the role of family experience is now in serious dispute." [Brand, C. (1996). The _g_ Factor: General Intelligence and Its Implications. Chichester, England: Wiley]

In Plomin's 2004 article, he discusses that one of the reasons why it may be difficult to pinpoint a genetic link to IQ is that a single gene may only account for something as small as 1% of the variation, such that you can never detect a difference by looking for one gene at a time. So, for those who are willing to embrace the genetic linkage, and would accept Plomin as an authority on the subject, why could the same not be true of environmental factors?

It may well be true that environmental factors account for only 1% of the variance each. I don't see the problem. We know the sum of the genetic influence and we know the remainder is due to the sum of all environmental and error components.

Often, we try to study single environmental factors to avoid the difficulty in interpreting findings with numerous variables. What if we can't detect any differences for a single environmental factor, such as SES, for the same reasons we can't detect significant differences related to a single gene?

It is relatively unimportant to identify causes of 1% in variance when we can identify the sum. There is no dispute that the sum of all environmental factors is equal to 100% minus the variance in the genetic component, minus the variance due to error. The end finding is completely consistent with the findings of scores of careful research programs.

Jensen: "One commentator likened the latest phase of the nature-nurture IQ debate to "a stomping match between Godzilla [that is, genes] and Bambi [that is, environment]."
See page 100 Miele (2002) - Intelligence, Race, and Genetics: Conversations with Arthur R. Jensen

 

[Waterdog]

This may be of interest to some of you:

Concordance rates of IQ scores

Evidence from family studies provides the main supporting evidence from which arguments about the relative roles of genetics and environment are constructed.

A large number of the study of twins reared apart was undertaken by Thomas Bouchard of the University of Minnesota starting in 1979. He “collected” pairs of separated twins from all over the world and reunited them while testing their personalities and IQs. Other studies at the same time concentrated on comparing the IQs of adopted people with those of their adopted parents and their biological parents or their siblings. Put all these studies together, which include the IQ tests of tens of thousands of individuals, and the table looks like this:

• Same person tested twice 87%
  
  Identical twins reared together 86%
  
  Identical twins reared apart 76%
  
  Fraternal twins reared together 55%
  
  Biological siblings reared together 47% (studies show that reared apart about 24%)
  
  Parents and children living together 40%
  
  Parents and children living apart 31%
  
  Adopted children living together 0%
  
  Unrelated people living apart 0%

from
Ridley, M. (1999). Genome: The autobiography of a species in 23 chapters. London: Fourth Estate Ltd.

The Minnesota Twins study really doesn't account for environment very well. The employ an inventory of items such as whether the households in which the separated twins are raised possesses power tools or encyclopedias. Based on this they have argued that the environments of the twins in the study were heterogeneous. However, the twins are not from "all over the world," as you say. They come from a few culturally homogeneous countries such as the US, UK, Australia, West Germany, and a few others that are quite similar as well--both internally homogeneous and similar to each other. All of these countries provide basically the same opportunities for developing IQ and the same cultural emphasis on IQ-related tasks. In addition, the MN twin study's inventory of items that supposedly shows how heterogeneous the households are could be described as rather arbitrary or even silly. There is a reason that so-called "social science" is distinguished from "hard science" such as physics or chemistry--it's simply impossible to really control any variables in a social science.

No one would deny that MZ twins are more similar then unrelated strangers, but this would only come as news to the most radical environmentalists. For most reasonable people, who believe that variation of traits in a population is partly due to environment and partly to genetics, the MN twins study is really not that enlightening, since it only tells us what we already knew. The beanfield analogy is most apt here. They are studying beans in one field where soil, light, and water are all constant. Not surprising at all that in that case, beans with the same genes don't show much variation. They have not looked at how beans with identical genes would develop in fields with radically differing soil quality, sunlight, water, etc. In fact, the authors of the MN twins study explicitly state that their study of within-group variance cannot be used to draw any conclusions about between-group variance. This last point is usually ignored by the radical genetic determinist crowd who misuse their work.