IQ-Brain Blog

Omega oils and IQ

Omega oils for IQ?
Omega oils and IQ / Cognitive ability.

A new place-bo-controlled, double blind study of 154 nine and 10 years old in Sweden appears to confirm that those children that are given Omega 3 and Omega 6 fatty acids may drastically improve their reading ability. In this study, the children were randomly assigned to three groups. The first group was given Omega 3 supplements, the second group Omega 6 supplements, and the control group was given an identical looking tablet which contained a placebo (palm oil). After three months, all the children were given Omega 3/6 capsules as part of the study. The children’s reading ability was measure with the aid of a computer-based ‘Logos’ test.

The authors of the study noted that children who were given fatty acids demonstrated significantly enhanced reading skills even after three months. Although none of the children had been diagnosed with ADHD, those children with mild attention issues experienced the greater improvement in reading with the administration of fatty acids.

The role of polyunsaturated fats in children’s learning and development is a growing area of interest. Matt Johnson, from the University of Gothenburg notes that the cell membranes in the brain are largely made up of polyunsaturated fats, and that some studies have noted that supplementation of fatty oils may enhance signal transmission betweeen nerve cells; this may explain some of the results seen in this study.

Other studies have failed to show a signicant association between fatty acid consumption and cognitive performance.

Analysis

Several interesting questions come to mind including whether the auhors would have controlled for the IQ level of children, and whether other cognifive skills (e.g. mathematical) might have also benefited from the fatty oil supplementation.

There is certaintly plenty a very interesting base to build on for future studies into the link between omega oils and IQ / cognitive performance.

Omega oils and IQ

The jury is still out as to whether the consumption of omega oils can lead to a lasting boost in IQ.

Rick Rosner, with an IQ of 192, incorporates the consumption of fish oil (as well as aspirin) into his daily breakfast diet. Despite the scant evidence, many intelligent people (including the author of this posting) supplement with fatty oils.

However, although there is some positive association between Omega oils and IQ, there are risks in supplementing with fatty acids. For instance, owing to the lack of regulation of supplements, the source of the fatty acids (particularly fish oils) could be contaminated, or could even contain mercury and other pollutants, which could theoretically negate any IQ benefits that fatty oil supplementation may bring. For this reason, people willing to take the risk should at least search our the purest grade fish oils, and keep these in a cool and dark environment  to help prevent the product from going off.

On a personal note, the number of studies confirming some positive cognitive effect from fatty oil supplementation seem too many to be spurious.

You can test your IQ at www.iq-brain.com

IQ genetics or environment? Both come into play

IQ genetics or environment
IQ genetics or environment?

IQ genetics or environment? Let’s provide a bit of background to the question. Many studies have been published which have investigated the issue and it is undeniable that there is a positive correlation between the IQ of offspring with that of their birth parents, especially the birth mother. A particularly intereting series of studies involved the comparison of adoptive children’s IQs with that of their birth parents and that of the adoptive parents. In a classic 1979 study, Scarr and Weinberg found that the correlation between the IQ of the adopted child and that of the adoptive parents was 0.13, which is lower than the IQ correlation between two random people off the street. This compares to 0.32 as the correlation coefficient between the IQs of adoptive children with that of their birth mothers. Fascinatingly, by the time that these adoptive children turned 18, the correlation coefficient between their IQ and that of their adoptive parents had dramatically fallen from an already low base of 0.13 to 0.06, which provides evidence that environmental factors (barring detrimental living conditions) have little bearing on the IQs of children over the longer term.

Several other types of clever studies including twins studies have also shed light on the question: IQ genetics or environment? Herrnstein and Murray also looked at kinship and adoption studies, including virtual twins (i.e. non-genetically related children that grow up concurrently in the same household). Segal (1997 and 2000) studied 90 virtual twins and found that the coefficient of correlation between these virtual siblings’ IQs was 0.27 (with a mean IQ difference of 15.4 points), which compares to 0.86 for identical twins reared together (6 points), and 0.47 for biological siblings reared together (14 points). Based on these results, it would appear that genetics over-power environmental factors in the long-run.

Strangely, Fischbein (1980) also found that heritability of IQ increases for the highest social classes (0.70), compared to 0.30 for the lowest social classes. Although some of the studies cited in this posting date back several decades, severely studies have largely reconfirmed results in that IQ is largely heritable, with 50-60% of the variability in IQ being explained by genetics as opposed to environmental factors.

IQ genetics or environment? The fade out effect

In 2015, a meta study by researchers at the University of Santa Barbara examined whether early intervention programmes designed to raise the IQ of young children had lasting effects over time. The lead researcher Protzko conduced 44 different trials involving 7,584 young children and found that the experimental group who had early intervention programmes lost their IQ gains after the programme was over (as opposed to the control group catching up).

It would appear that once the programmes had ceased, that the cohort of intervention children did not seek out intellectual pursuits that would match their newly (and it would appear temporarily) boosted IQ level, and that they would revert to their normal activities, leading any gains to fade out over time. So while Head Start type of programmes may confer a temporary IQ benefit, these gains are unlikely to be permanent.

iq-brain.com perspective

Protzko’s latest study reinforces the notion that IQ is likely to be heritable, and that environmental factors may of course have short-lived positive effects, but that barring the existence of corrosive and unhealthy environments (e.g. drug use, terrible diets, stress, violence) genetics remain the primary explanatory factor of intellectual ability and IQ standing, certainly as children reach adulthood.

As expressed previously, this is not to say that parents should not invest in providing the best possible environments for their children: in fact, the silver lining in the study suggests that some well crafted temporary intervention programmes may in fact produce temporary boosts in IQ, which if parents are capable of sustaining via intellectually-challenging environments, may allow children to get through school with greater ease, which in itself is half the battle won when raising a child. There is also the likelihood of an important interplay between genetics and the environent.

That said, providing a “good”, not necessarily outstanding environment is likely to be sufficient for your child to live up to its full IQ potential. So for those concerned about lower IQs, teaching your children good work ethic and perseverence, in addition to making sure they have a pleasant and happy environment, may represent a better solution than hoping for miracles from early start intervention programmes or being too strict with your kids.

Provided by www.iq-brain.com

IQ differences between siblings

IQ differences between siblings are not meaningful
IQ differences between siblings are not meaningful

Researchers at the University of Illinois have published the results of the largest-ever “within family” evaluation of IQ and personality difference among siblings. The study helps shed light on IQ differences between siblings.

This very large sample study (backed by the National Institute on Aging which is part of the National Institute of Health) looked at 377,000 high school students and evaluated IQ differences between siblings, as well as differences in personality which might be influenced by the chronological order of birth.

The results of the study are clear: IQ differences between siblings are in fact influenced by birth order. First-born children on average will have a statistically significant one IQ point advantage relative to their younger siblings. Although the IQ differences between siblings are statistically significant, they are hardly meaningful as a one point IQ differential cannot produce any perceptible differences in intelligence or cognitive ability.

The study found that first-born children tend to be more outgoing and conscientious, in addition to have slightly higher IQ scores on average.

IQ differences between siblings: iq-brain.com take on the study

At iq-brain.com , we believe (based on several comprehensive studies on IQ and intelligence) that genetics factors explain the majority of the variance in IQ scores generally. However, we do acknowledge that environmental factors may have an influence on IQ scores and cognitive ability generally. Here is our analysis on the study measuring IQ differences between siblings.

On the one hand, older siblings will tend to get more parental attention and contact than their younger siblings. First-time parents are probably more likely to be more cautious with their first child (e.g. maternal contact and attention, which have been shown to increase IQ – see breastfeeding post IQ and breastfeeding). In support of the findings, older children will also need to “figure it out” as they progress through life, learning by trial and error.

The contra argument is that younger siblings, if the age gap is not too large, will tend to play and learn from older siblings, resulting in a transfer of knowledge from the older sibling to the younger one. This accelerated learning could also be an IQ booster for younger siblings, allowing for ‘catch up’ to take place.

Importantly, the IQ differential of one point, although statistically significant is not material. Based on the above two arguments however, it would be interesting to drill down into the results to test whether older siblings display a higher level of fluid intelligence (as they “figure it out”) relative to younger siblings, who are more likely to use their sequential processing and crystallized intelligence to follow in the footsteps of their older siblings.

article provided by www.iq-brain.com a leader in online fluid IQ testing.

IQ and breastfeeding

IQ and breastfeeding
IQ and Breastfeeding are positively associated variables

A recent Brazilian study has found that longer-breastfeeding was linked to higher IQ. The study, published in the prestigious peer-reviewed journal the Lancet, began with 5,914 newborn babies in 1982, and were able to follow up with 3.493 of those individuals three decades later.

The study found that those babies who had been breastfed for up to a year, as opposed to those who has been breastfeed for one month or less, score up to 4 IQ points on average when tested by the age of 30.  The study also found that, perhaps as a consequence of developing higher IQs, the follow-up cohort had 0.9 years of additional schooling and that the earnings were higher by a third of the average income. The authors took the care of controlling for a number of confounding variables such as maternal education, birth weight of the child and smoking during pregnancy.

According to this study, IQ and breastfeeding are positively correlated, which gives credence to the UK Government’s stance that “breast is best”.

Although some have considered that the follow-up rate of 59% is relatively weak, (as a rule of thumb, a drop-out rate of 20% or more is considered to be reasonably high)  there is no suggestion that the individuals who were traceable during the follow-up would represent a group with directionally predictable IQ behaviors. The fear is of course that people who were traceable would have had higher IQ, although it is equally safe to assume that individuals with the highest IQs would be the most mobile, and could therefore have been more difficult to trace in the follow up period. With a final sample of c.3,500, is it reasonably safe to assume that the results of the study ought not to be compromised owing to the survivorship rate of the original sample of babies.

Another criticism of the study is that mothers were asked to recall breastfeeding habits three decades later, which could have resulted in recollection errors, which could distort the ability to accurately study the link between IQ and breastfeeding. This is perhaps the study’s greatest weakness, although mother’s tend to have a fairly good recollection of details surrounding the birth of a child.

IQ and breastfeeding are positively correlated: although you need the right genes.

In any case, the recent Brazilian study backs several prior research studies that have also found a correlation between IQ and breastfeeding. A 2007 study of UK and New Zealand newborns has also found that IQ and breastfeeding are positively correlated variables. Specifically, the researchers found that babies which had carried the C-genotype of the gene known as FADS2 (90% of people possess the C genotypes, while 10% possess the G genotype), a gene which is closely associated with the processing of fatty acids in diets, recorded average IQs of up to 7 points higher than children who either possessed the G genotype or who were not breastfed. This led to the conclusion that the vast majority of people are genetically predisposed to get an IQ boost from breastfeeding.

So the emerging evidence appears to be that IQ and breastfeeding are positively linked, and if you are a mother who is able to breastfeed your child, then you should do this.  If you are unable to breastfeed, either because it doesn’t work or is too painful or stressful, then there is no point in beating yourself up over the issue as heritability is likely to be a much stronger variable than breastfeeding. But that said, the most important takeaway is that mothers should nurture their babies in the best way that they can.

For more information about IQ scores and IQ testing, visit www.iq-brain.com

Intellectual elites

Intellectual elites to remain at the pinnacle
Intellectual elites to remain at the pinnacle of knowledge-based economies

In a recent article (An Hereditary Meritocracy), the Economist magazine argues that a new class of intellectual aristocracy is taking over the United States of America. The article suggests that intellectual elites are more likely to pair up (i.e. find a mate) based on common values such as university education and drive, creating favourable learning environments for children, which in turn is bolsters the chances of such children gaining access to the US’ best educational institutions and in particular the Ivy league.

The article also cites that scores achieved on standardized aptitude tests (SATs) are positively correlated to parental incomes, which is argued to exacerbate the intellectual elites’ ability to cling to power.

Although I have no reason to doubt the strong positive association between parental incomes and SAT scores, the Economist magazine sidesteps the fundamental explanatory factor which is perpetuating the success of the intellectual elites: intelligence or IQ.

As I have argued in several previous postings, IQ does not guarantee success. However, higher IQ, on average, is positively associated with academic success, which in turn is associated with the ability to enter better rated universities, which in turn is associated with better job prospects for graduates, and yes – you’ve guessed it, higher parental incomes. In other words, intelligence (which is a form of natural ability), paired with hard work, remains the best predictor of success, and is at the heart of the success of the intellectual elites, whether in the United States or elsewhere.

As the Economist magazine correctly points out, between 1960 and 2005, the share of men with university degrees who married women with university degrees has nearly doubled from 25% to 48%. This is of course largely explained by the emancipation of women since the second World War, and the fact that the representation of women in higher education (c.60% of university graduates in the US are women) has made it easier for smarter men to pair up with smarter women. (One must recall that the average IQ of university students is c.110 points vs 100 for the population as a whole).

But again, all the evidence points towards first and foremost, intelligence, and perhaps in a distant second position, environment as the root cause of the success of the American intellectual elites. But unlike the Economist, I de-emphasize the importance of environment. As reported upon here a number of recent robust studies have definitively shown that IQ is largely genetic and that learning environment plays relatively little part in the determination of intelligence over one’s lifetime and therefore success. In other words, heritability is likely to play a larger role than say the price tag on the kindergarten or school that you decide to send your child to. Even Andreas Schleicher, the head of the OECD’s education team, admits in an article published in the Economist, that investment in early years schooling does not necessarily translates into learning gains.

The unfortunate reality is that IQ, and not educational environment, is the root cause of the growth (and what is likely to be the persistence) of intellectual elites. Sadly, blaming parental incomes, or poor nurseries, or educational funding arrangements is, as a strategy, more likely to win votes as opposed to throwing in the white towel to genetics. (Rather than electioneering and scapegoating, surely the sensible strategy would be to standardize nursery educational provision based on ‘best in class’ practices and empirical data?). But if a magazine such as the Economist is unable (or unwilling?) to discuss matters in full, and instead insistent on reinforcing populist wives tales about the root of inequality, then public funds will continue to be mis-allocated and the witch hunt will continue while the intellectual elites consolidate gains in the upper echelons of our societies.

To test your IQ, click here.

Provided by www.iq-brain.com

IQ and schizophrenia

John Nash had high IQ and schizophrenia
IQ and schizophrenia are negatively correlated: although John Nash proves that high IQ does not guarantee protection

IQ and schizophrenia: A recent study by Virginia Commonwealth University and Lund University sought to evaluate the relationship between IQ and schizophrenia. In popular culture, IQ and schizophrenia are usually thought to be positively associated. For instance, the famous mathematician John Nash shared a Nobel prize in economics for his work on game theory and differential geometry. John Nash’s schizophrenia was portrayed in the movie A Beautiful Mind.

The recently published study tracked 1.2 million Swedish males aged 18-20 born between 1951 and 1975, and monitored the frequency of schizophrenia-related hospitalizations over a 24-year period. The founding disproved popular theory that IQ and schizophrenia are positively correlated. In fact, the findings of the study suggest that higher IQ is negatively correlated with schizophrenia-related hospitalizations. The authors of the study conclude that high IQ may confer some degree of protective benefit against schizophrenia.

IQ and schizophrenia: the impact of drugs

One of the authors of the study pointed out that “if you are really smart,your genes for schizophrenia do not have much of a chance of acting”. Although high IQ and schizophrenia are negatively correlated, having a high IQ does not eliminate the risk of developing schizophrenia in young adults. It is thought that early drug use, traumatic childhood experiences and genetic predispositions may increase the risk of developing schizophrenia.

The study provides clear evidence that young people with a genetic predisposition and a family history of schizophrenia should avoid drugs at all cost. I have previously posted  about the link between marijuana use, IQ as well as schizophrenia. Drugs, whether hard or soft, may have a detrimental effect of IQ, which in turn may not only decrease intelligence of drug takers, but also give schizophrenia genes a larger chance of acting. This may cause a downward spiral as psychotic episodes and onset of schizophrenia have also been linked to lower IQ.

To test your IQ online, accurately and confidentially, click here.

 

 

 

IQ is genetic

IQ is genetic
IQ is genetic and shared environmental impacts are negligible

I have written quite a few postings on the  heritability of IQ. A number of recent studies  have confirm the point that variances in IQ can be explained by genetic factors (to the tune of about 60%), while environmental factors account for up to 40% of variability in IQ. These finding represented a departure from the earlier studies which had suggested that 50% of IQ was heritable. The literature is increasingly clear that nature plays  a bigger impact than nurture .

A new series of studies have weighed in on the debate, and findings have only strengthened the camp of IQ being genetic. Florida State University recently published a study which employed the well regarded database called the National Longitudinal Study of Adolescent Health. The study looked at the IQs of adopted children and their adoptive parents. The study concludes that there was little evidence to suggest that environmental factors and parenting had any level of impact on the IQs of the adoptive children. Further, it even went on to conclude that “maternal attachment” was negatively correlated to the IQs of the adoptive children.

Another important study was from Kings College London, which is at the forefront of the analysis of the human genome. KCL researchers employed “Genome Wide Complex Trait Analysis”. The researchers found that 94% of the relationship between socioeconomic status (SES) and IQ was mediated by genetic transmission by the age of 7, and 56% by the age of 12. Again, the overall conclusion is that IQ is genetic and that SES is also largely rooted in genes.

So IQ is genetic, are parents wasting their time?

The proportion of IQ which is said to be attributable to ‘environmental’ factors may be up to 40%, although recent studies clearly point towards the increasing strength of the genetic explanatory factor. So what is going on? Well, the term ‘environmental’ factors is in fact misleading. That is, the body of literature calls these ‘non shared’ environmental factors. In other words, these are environmental factors that go beyond household level of quality of life. These non-shared environmental factors may be the result of an accident, illness, or specific life events that may not even be share by siblings and even identical twins.

The conclusions of this research also points to the fact that parents need to take a breather. Pushing children for greater academic achievement beyond their natural ability may be somewhat counterproductive. Good, rather than great home and learning environments as well as teaching children positive work habits should be sufficient for the children to achieve their full potential. This also suggests throwing money at the problem is unlikely to help. The extra cash is probably best saved and spent on a trip to Disney Land and going on family holidays and having a good time.

That said, a favorable home and learning environments may create short term boosts in academic achievement, which in turn helps children get through their schooling with greater relative ease. And each additional year of schooling is correlated with higher crystallized intelligence which is one important component of overall intelligence.

There is little doubt that genetics play a part, which means that parents should give themselves a break and focus on their own / and their children’s happiness.

For more about IQ testing, click here.

Superhuman intelligence: the new Cold War?

Superhuman intelligence: the new Cold War?
Superhuman intelligence: the new Cold War?

In my last blog posting, I explained how the body of academic literature on human intelligence is increasingly clear: IQ tends to be largely inheritable, with up to 60% of IQ variability explained by genetic factors.

I also introduced recent research at US San Francisco which highlighted the ‘VS’ variant of a gene called KL. The VS variant of the KL gene (known as KL-VS) may explain up to 3% of variability in human cognition  (equivalent to roughly 6 IQ points). This has led some people to question whether researchers may be able to manufacture superhuman intelligence by manipulating genes.

6 IQ points may not sound like a lot, but over a population, this will have a noticeable difference. Literacy rates would be expected to improve, and more people might be inclined to pursue a higher level of education.

But superhuman intelligence would start with the manipulation of not just KL-VS, but 1000s of genes which are thought to have an influence on human cognition and IQ. You would only need to find a way to ‘switch on’ the positive variants of the IQ genes, and to have a 1/200th of an IQ point impact over the 10,000 genes to yield a 50 IQ point advantage. Given that the average IQ is advanced nations is thought to be around 100 IQ points, this would mean that genetically modified brains could end up with 150+ IQs, which is currently a score recorded by 1 in 1,125 people (16 SD). And what if you found that the average impact was 1/100th on an IQ point, than you would be talking about an IQ score of 200 points (currently 1 in 4.8 million people). Where does superhuman intelligence start? IQs of 150 are rare, but found, so this might not constitute superhuman intelligence. But at 200+, there is little doubt that this constitutes superhuman intelligence.

Superhuman intelligence: genomics may be the gateway

Stephen Hsu, a theoretical physicist from Michigan State University is a scientific advisor to the Beijing Genomics Institute (BGI). Hsu believes that superhuman intelligence may be closer than we think.

BGI is currently trying to map the genome based on 2,000 individuals with some of the highest IQs ever recorded. The purpose of the exercise is to shed light on genetic sequencing that is associated with higher order cognitive ability. The end goal is to be able to offer treatment and embryonic selectivity to create babies with superhuman intelligence.

Hsu published an article in which he speculates what humans with superhuman intelligence might look like and what types of skills these people may possess. The results are both amazing and frightening, and beyond comprehension for most of the human population with ‘normal’ IQs.

I would personally be the first one to sign up for a treatment which might increase my IQ by 6 points. 10-15 IQ points, quite possibly. But beyond this level, I am not so sure. Super-charging human cognition to the existing limits of human brains is both difficult to imagine, and the consequences difficult to predict. I see more value in helping people who find themselves, through no fault of their own, towards the bottom end of the distribution as this could really help life outcomes of such people. There is no question when dealing at the upper end, the ethical considerations are immense.

Superhuman intelligence: the new Cold War?

Let’s analyise some of the ethical consequences for a minute. The benefits could be dramatic: eradication of diseases, solving of complex mathematical problems which have eluded humans for centuries, space travel, dramatic explosions in technology. But the more harmful consequences are also quite obvious: a more complex society, supercharged criminal networks, inequality and potential abuses of power and tyranny.

But it is all good and well to think Science Fition, but the real problem is that even if the technology were here today, some countries may have bans on the technology on ethical grounds. But other countries might not. And therein creates the prisoner’s dilemma and game theory dynamics which may be highly problematic.

Would the West dig its heals as other less ethical countries start producing babies and armies with superhuman intelligence? This type of technology may be 10-15 years away. But when it comes, it may revolutionize the world as we now if today. For the better? I am not so sure.

To test your IQ, click here.

Superhuman intelligence

Superhuman intelligence
Superhuman intelligence may be closer than you think

Intelligence or IQ is more deeply rooted in genetics than it is in environment factors or upbringing. This is what researchers at Kings College London have found that genetics explain more than 60% of the variability in IQ test results. According to this study, nature wins  . This finding may explain why several prior studies have shown that children of professionals will tend to have significantly higher IQs than children of unskilled workers. This may also help explain why nearly 70% of students who attend the UK’s elite universities (Oxford, Cambridge, Durham, Imperial, St Andrews and the LSE) hail from public schools (i.e. the British term of fee paying high schools) which again means that most of these pupils hail from middle class backgrounds with professional parents. But the Kings College study also found that children were more likely to inherit other genetic traits that would, in addition to IQ, play a role in academic success including motivation and hard work.

IQ is largely heritable, is it possible to achieve super human intelligence? Researchers at the University of California at San Francisco have been studying the role of the ageing of klotho, a protein encoded by a gene called KL. A particular version of this gene, known as KL-Vs, has been shown to be associated with longevity, made possible through the reduction of age-related heart disease. But researchers made a startling discovery: the KL-VS not only curbs ageing, but it also boosts cognition faculties, regardless of a persons age, by the equivalent of 6 IQ points. Ironically, it does not curb cognitive decline, so it would appear to be a one time boost. Although six points will not result in superhuman intelligence, this variant of the gene is believed to explain up to 3% of the variability in human cognitive ability, which is multiples higher than any other gene previously identified to play a role on human cognition. The researchers than tested this finding by injecting mice with a similar variant of the gene and found that genetically engineered mice were much more adept at making their way through a maze than those mice without the VS equivalent version of the gene.

Superhuman intelligence: the answer is in the genes

Now, what if I told you that there are 1000s of genes that are believed to have an impact on cognition? And although their individual effects could be much less than the 3% caused by KL-VS, it would only take 1/10th of 1 IQ point, to add a total of 100 IQ points, should all of these ‘positive’ variants of these 1000 genes be switched on. This would in fact lead to superhuman intelligence.

Although this may sound like science fiction today, the Beijing Genomics Institute is currently running a trial to map the genomes of 2,000 of the world’s smartest people.

Frighteningly, superhuman intelligence may be closer than one thinks. I will write more about this in my next blog posting. The ethical issues are immense.

To test your intelligence accurately, click here or visit www.iq-brain.com.

IQ heritability

Twins and IQ heritability
Twins are a good starting point in the evaluation of IQ heritability

I have previously written about IQ heritability. It is the age old question of nature versus nurture. There are a reasonably large number of studies which examines IQ heritability. While the existing body of literature refutes anti-genetics ideology, it also lends support to environmental effects as well. So the extant body of literature of IQ heritability also suggests that the environment plays an important part in explaining some of the IQ variances observed between groups. The most interesting studies that currently exist are kinship and adoptive studies. For example some of the kinship studies look at fraternal vs. identical twins, which represent a great starting point to establish IQ heritability, namely how differences in IQ scores may be explained by genetic and/or environmental factors. This is so because it is not unreasonable to assume that fraternal twins (who are born together, but share only 50% of genes – the same as any normal siblings) are likely to benefit from the same environment as they grow up. On this basis, comparing the variability of fraternal twins IQ scores with identical twins (who share 100% of the same genes) reveals important and undeniable evidence in respect of the debate. These studies have shown that 50% of IQ is likely to be heritable, and initial studies from the late 1970s have been confirmed over the last few decades.

IQ heritability: what the existing literature says.

Adoption studies are also particularly interesting in assessing IQ heritability. That is, if environment/nurture is a leading explanatory variable for the variability in IQ scores, then one would expect that adoptive children’s IQs should converge towards the performance of any siblings residing in their adoptive households, including any genetic children of the adoptive parents or the adoptive parents themselves. The Texan adoptive study for instance, found that at age 8, the correlation between IQ scores between the child and adoptive parents was 0.13, compared to 0.32 as compared to their genetic mothers. When the children were re-tested by the age of 18, the IQ correlation coefficient with adoptive mothers and fathers had fallen to 0.02 and 0.10 respectively, while IQ correlation coefficients with biological mothers has increased to 0.48.  The conclusions here are that genetics prevail over the long run, giving credence to the notion of IQ heritability.

I will write further on this topic in my next posting.

For more information on IQ and to test your IQ online, you can click here or visit www.iq-brain.com