Most of intelligence is in fact genetic according to new study...

[Phier]

http://www.sciencedirect.com/science...60289614000889

Abstract

The association between family/parenting and offspring IQ remains the matter of debate because of threats related to genetic confounding. The current study is designed to shed some light on this association by examining the influence of parenting influences on adolescent and young adult IQ scores. To do so, a nationally representative sample of youth is analyzed along with a sample of adoptees. The sample of adoptees is able to more fully control for genetic confounding. The results of the study revealed that there is only a marginal and inconsistent influence of parenting on offspring IQ in adolescence and young adulthood. These weak associations were detected in both the nationally representative sample and the adoptee subsample. Sensitivity analyses that focused only on monozygotic twins also revealed no consistent associations between parenting/family measures and verbal intelligence. Taken together, the results of these statistical models indicate that family and parenting characteristics are not significant contributors to variation in IQ scores. The implications of this study are discussed in relation to research examining the effects of family/parenting on offspring IQ scores.

I've always felt that genetics played the largest role, but I assumed that there had to be some environmental contribution as well that could make a difference. Perhaps I was wrong and the implications of this study would be far reaching. I have a meeting to get to in an hour so I'll leave this here for now, and if anyone has a link to a full study please post it.

[sumskilz]

This is consistent with the previous finding that the heritability of adult IQ is about 80%.

Abstract: The powerful quantitative genetic design of identical and fraternal twins reared apart (112 pairs) and matched twins reared together (111 pairs) was employed to assess the extent of genetic influence on individual differences in cognitive abilities during the last half of the life span. General cognitive ability yielded a heritability estimate of about .80 in two assessments 3 years apart as part of the Swedish Adoption/Twin Study of Aging. This is one of the highest heritabilities reported for a behavioral trait. Across the two ages, average heritabilities are about .60 for verbal tests, .50 for spatial and speed-of-processing tests, and .40 for memory tests. For general cognitive ability, the phenotypic stability across the 3 years is .92 and stable genetic factors account for nearly 90% this stability. These findings suggest that general cognitive ability is a reasonable target for research that aims to identify specific genes for complex traits.

Variability and stability in cognitive abilities are largely genetic later in life

Also...

Abstract: The longitudinal rank-order stability of cognitive ability increases dramatically over the life span. Theoretical perspectives differ in their emphasis on genetic mechanisms in explaining the longitudinal stability of cognition and how stability changes with development. However, the patterns of stability of genetic and environmental influences on cognition over the life span remain poorly understood. We searched for longitudinal studies of cognition that reported raw genetically informative longitudinal correlations or parameter estimates from longitudinal behavior genetic models. We identified 150 combinations of time points and measures from 15 independent longitudinal samples. In total, longitudinal data came from 4,548 monozygotic twin pairs raised together, 7,777 dizygotic twin pairs raised together, 34 monozygotic twin pairs raised apart, 78 dizygotic twin pairs raised apart, 141 adoptive sibling pairs, and 143 nonadoptive sibling pairs, ranging in age from infancy through late adulthood. At all ages, cross-time genetic correlations and shared environmental correlations were substantially larger than cross-time nonshared environmental correlations. Cross-time correlations for genetic and shared environmental components were, respectively, low and moderate during early childhood, increased sharply over child development, and remained high from adolescence through late adulthood. Cross-time correlations for nonshared environmental components were low across childhood and gradually increased to moderate magnitudes in adulthood. Increasing phenotypic stability over child development was almost entirely mediated by genetic factors. Time-based decay of genetic and shared environmental stability was more pronounced earlier in child development. Results are interpreted in reference to theories of gene–environment correlation and interaction.

Continuity of Genetic and Environmental Influences on Cognition Across the Life Span: A Meta-Analysis of Longitudinal Twin and Adoption Studies

[Elfdude]

Of course most of IQ is genetic but that has little to do with childrearing and what the best methodology of parenting is. IQ is pretty much set after middle school anyways. The largest IQ effects are seen in early childhood. Furthermore in human development IQ is not the only significant marker of child-rearing. You can have a great IQ and no social skills and still fail at life.

Here's a good study on child rearing:

Follow-up assessment of the participants involved in the project has been ongoing. So far, outcomes have been measured at ages 3, 4, 5, 6.5, 8, 12, 15, 21, and 30. The areas covered were cognitive functioning, academic skills, educational attainment, employment, parenthood, and social adjustment. The significant findings of the experiment were as follows:

Impact of child care/preschool on reading and math achievement, and cognitive ability, at age 21:


An increase of 1.8 grade levels in reading achievement
An increase of 1.3 grade levels in math achievement
A modest increase in Full-Scale IQ (4.4 points), and in Verbal IQ (4.2 points).


Impact of child care/preschool on life outcomes at age 21:


Completion of a half-year more of education
Much higher percentage enrolled in school at age 21 (42 percent vs. 20 percent)
Much higher percentage attended, or still attending, a 4-year college (36 percent vs. 14 percent)
Much higher percentage engaged in skilled jobs (47 percent vs. 27 percent)
Much lower percentage of teen-aged parents (26 percent vs. 45 percent)
Reduction of criminal activity

Statistically significant outcomes at age 30:
Four times more likely to have graduated from a four-year college (23 percent vs. 6 percent)
More likely to have been employed consistently over the previous two years (74 percent vs. 53 percent)
Five times less likely to have used public assistance in the previous seven years (4 percent vs. 20 percent)
Delayed becoming parents by average of almost two years
(Most recent information from Developmental Psychology, January 18, 2012, cited in uncnews.unc.edu, January 19, 2012)


The project concluded that high quality, educational child care from early infancy was therefore of utmost importance.

http://en.wikipedia.org/wiki/Abeceda...ention_Project

Methinks a Republican Floridian Criminology professor is simply trying to negate 'liberal' (aka scientific) child rearing philosophy and missing the point entirely while he's at it.

[sumskilz]

Hmm...

At age 15, the 4.6 point WISC-R IQ difference in the Abecedarian Project was not statistically significant (Farran, in press). The mean ability test score of the intervention group was somewhat higher than the control group's at 6 months, shortly after they entered the Project. Although their score remained in the average range throughout, by 18 months, it was appreciably higher than the control group's only because the mean score of the control group had declined until it began, by 48 months, a steady recovery. In general, the experimental group never increased in IQ, but remained in the average range. Nor did the control group decline into mental retardation. The final IQ difference, not incidentally, was about the same as the difference at 6 months; a difference that Ramey, Yeates, and Short (1984) admit cannot be attributed to the intervention.

In regard to this conspicuous lack of enduring effect in the Abecedarian Project, Spitz (1999, p. 283) raised a question and then proceeded to answer it: "What happened during those first 1.6 months at the day care centre to produce an effect worth 6 points, whereas an additional 4 1/2 years of massive intervention ended with virtually no effect? It seems to me that it is not unreasonable to infer that nothing happened, but rather, some initial difference in the control and intervention groups had (by chance) escaped randomisation, and revealed itself at six months of age." We found similar problems with the IHDP.

After a scrupulous, detailed, and even-handed reevaluation of both the Abecedarian and IHDP projects Bruer (1999, p. 172) also concluded they "... hardly support a claim that early interventions have substantial, long-lasting, and positive effects on lifelong intelligence and school achievement." He goes on to add: "One of the greatest abuses to the cause of children is misrepresenting the effects of early-intervention programs" (p. 173). The pathetic collective tragedy arising from such naive environmentalism and misguided egalitarianism is that all the wasted resources could be used much more productively to target specific health-related and social problems with some beneficial results, on a more realistic and less idealistic and grandiose scale to be sure.

Early Generic Educational Intervention Has No Enduring Effect On Intelligence and Does Not Prevent Mental Retardation

[Kyriakos]

Makes sense, given that if one genetically has X<--->Y complexity of sensing (and thinking, later on) stuff, then the actual education and other chances will still be one factor in that bounded (but huge) realm of possibilities for development.
Compared to one who has notably less potential the outcome is virtually always in favor of the former.

(Do note that 'intelligence' only connotes actual degree of complexity in sensing/thinking. It does not mean the more intelligent person will be more successful, or happier, or more known etc, or even visibly taken for more intelligent. If one is super-intelligent but also has a myriad psychological issues, chances are he/she will sink).

[Elfdude]

Hmm...

Early Generic Educational Intervention Has No Enduring Effect On Intelligence and Does Not Prevent Mental Retardation

This is a fantastic paper but I don't find it compelling regarding the effects of early intervention. The particular benefits of the Abecedarian Project were not intellect quotient gains because in the 1980's the chief concern was that children would become mentally retarded at a higher rate. While it's true that socioeconomic status can decrease a child's IQ by a full standard deviation, it's rare for a child lacking genetic effects to become mentally retarded. Genetics at this point in time was not understood. What was demonstrated with the study however was that the intervention had a dramatic effect on the children's success when considering college and use of public resources. Which is to say, these children were more likely to become educated, and more likely to be successful in life on their own. This was an unexpected but real benefit to early intervention.

Anyways way to find a better study.

[Stario]

I've always felt that genetics played the largest role, but I assumed that there had to be some environmental contribution as well that could make a difference.

Environmental factors such as womb condition, nutrition, breast feeding, pollution (Baghurst et al. 1992, re: lead and IQ study comes to my mind) etc. do contribute.

[Adar]

I've moved from a very poor socio-economic context to a very good one dwhich have given me some rather interesting experiences of both intelligence (as per Phiers OP) and general academic success (which elfdude talk about) in my surroundings.

When it comes to outright intelligence I believe that it is mostly genetic. Of the kids I went to elementary school with, pretty much all the children who did well at maths and in military testing also had smart parents.

But for career success there are also a lot of other factors weighting in. The Swedish school system used to provide almost no choice which put elementary school children from non-academic homes in the same schools as children from academic homes based on where they lived. This combined with the city architecture in most Swedish cities ensured a certain level of mixing. So I (from a lower middle class) went to school with both some academic children and a vast majority of children from a more challenging social-economic background.

Out of my social circle, pretty much all the intelligent children got degrees, while the not so academically gifted children got other jobs. But what's surprising me at university is that there is still is a very large population of not so intelligent people. Most of these students does however seem to have been raised in more affluent areas than my own. So I guess that being brought up in a "good" school drastically increase the chance of getting an academic degree despite not being very smart.

We got a lot of nice articles quoted above. But anecdotal evidence strongly suggest that both Phiers and elfdudes studies may be correct at the same time without any major conflict between them.

[Alkaline Earth]

I am going to assume that intelligence=IQ

Most of intelligence is in fact genetic

Can this statement be quantified in lab conditions? Additionally, what exactly does having a higher IQ guarantee?

My guess is that it cannot be quantified and that there are no guarantees. Furthermore, all humans are 99.9% identical in genetic makeup, and consequently, any difference in IQ between humans would be caused by environmental conditions, which include mothers drinking/smoking, eating paint lead as a kid, and not getting enough iodine into your diet.

[sumskilz]

Furthermore, all humans are 99.9% identical in genetic makeup, and consequently, any difference in IQ between humans would be caused by environmental conditions, which include mothers drinking/smoking, eating paint lead as a kid, and not getting enough iodine into your diet.

The 99.9% figure is not the number of identical genes, it’s the number of nucleotide sequences that are the same. A single gene is a long chain of nucleotides, and a single nucleotide mutation can significantly alter how the entire gene operates. That also doesn't take into account the number of repetitions which probably accounts for most of human variation. For example, having four repetitions of the MAOA gene (which codes for an enzyme that breaks down noradrenaline, adrenaline, serotonin, and dopamine) makes you typical. The lower the number of repetitions a person has, the more prone to violence and impulsive behavior they will be. The most severe being those with only one repetition, which is known as Brunner Syndrome, who are mildly mentally handicapped and extremely dangerous. If you're going by the methodology used to determine the 99.9% figure, a person with Brunner Syndrone is no different than a typical person, yet it is a genetic disorder. In other words, the 99.9% figure doesn't really mean much. Or maybe it does, because 0.1% of 3 billion is still a very large number. That's 3 million differences on average between any two individuals.

No one who knows what they're talking about estimates the heritability of IQ lower than 50%. Estimates range from about 50-85%.

I'll quote a bit from another thread...

If the allele frequency in a particular population is fixed, then the genetic contribution to ultimate IQ outcomes is fixed. Since heritability is a measure of the total genetic portion of the existing diversity within a population, the more non-genetic factors that contribute to diversity of outcomes that exist, the smaller the relative percentage genetic factors contribute, and thus the smaller the measured heritability will be. Thus stating all the non-genetic factors of an attribute that has been measured to be highly heritable only reinforces just how robust the effect of genetics is on the outcome...

Individual environmental factors need not be accounted for at all because environment is a complicated and abstract thing – it is everything that is not genetic. Consider the difference of IQ correlation between monozygotic and dizygotic twin pairs – .86 for MZ pairs and .60 for DZ pairs. The issue is that these correlations are the result of both genes and shared environment. It is the difference between them that can only be accounted for by genetics (or so the thinking has gone). So the MZ twins sharing 100% or their DNA rather than an average of 50% of their DNA resulted in an additional correlation of .26 with the same level of environment sharing. Thus the thinking was that if 50% of genetics accounts for .26 of the correlation then doubling that will get you the total heritability of .52, this is how a lot of those old studies arrived at 50% heritability, but anyone who understands how genes actually function will know that this is way too low, because sharing one allele at a particular locus only sometimes results in the same phenotype whereas sharing two alleles at the same locus almost always results in the same phenotype. The phenotypic similarity of MZ twins is actually much higher than twice that of the DZ twins, and so much more complicated calculations are needed.

A meta-analysis found the heritability of adult IQ to be about .85
http://cdp.sagepub.com/content/13/4/148

American Psychological Association states heritability of post-adolescent IQ to be .75
http://psycnet.apa.org/?&fa=main.doi...3-066X.51.2.77

This study found a heritability estimate of about .80
http://link.springer.com/article/10.1007%2FBF01067188

You can follow the debate there between Caelifer_1991 and me, in which he argues 55-65% is more likely. There are a number of other studies posted: http://www.twcenter.net/forums/showt...1#post14216552