Evo
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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.hitssquad said:
Questions on _g_ and intelligence
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Mandrake
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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.
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.
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.
I didn't quote the sentence. What part of the material you quoted is significant and derived from the study?
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.
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.
And, unlike some folks, I understood it.
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.
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.
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.
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
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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.
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.
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How much (range)? How extensively has this been tested?Mandrake said:
I'm taking this step-by-step, and per hitssquad's Jensen quote, _g_ correlations are most solidly demonstrated in the US.
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
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Did Robert Plomin give up his attempt to identify genes linked to IQ
Did Robert Plomin give up his 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?Evo said:
Did Robert Plomin give up his attempt to identify genes linked to IQ?
Mandrake
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So far, hitsquad seems to be telling you that you have ducked his question.Evo said:
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
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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.hitssquad said:
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/
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BlackVision
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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.Evo said:
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.
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Mandrake
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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.Nereid said:
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.
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
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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.Evo said:
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
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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 betweenBlackVision said:
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
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Using Questia as an index for social science texts
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.Mandrake said:
Evo
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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.Mandrake said:
The study shows that environment is a substantially significant factor in increased IQ in the children studied and they are continuing this study.Mandrake said:
Your opinion means nothing to me Mandrake. No, I was trying to get BV to answer my questions, which he kept "dodging".Mandrake said:
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Evo
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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.Mandrake said:
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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
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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
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Exactly which questions am I "dodging"? What an ironic accusation coming from you.Evo said:
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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
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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.Evo said:
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
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It is much better than The _g_ Factor.hitssquad said:
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
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I previously referenced this paper from Intelligence:Moonbear said:
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
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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:
from
Ridley, M. (1999). Genome: The autobiography of a species in 23 chapters. London: Fourth Estate Ltd.
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.
nuenke
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Moonbear said:
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.
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nuenke said:
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.
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
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Definitions of heritability and environment and introduction to concept of variance
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.Moonbear said:
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.
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.
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.
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).
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.
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.
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.
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.
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hitssquad said:
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.
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
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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.nuenke said:
Mandrake
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The Shared Environment
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]
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
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.Moonbear said:
More likely is that genetic expression increases.
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]
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.
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
Mandrake said:
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.