IQ genetics or environment? A bit of both really but more genetics

 

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 strong 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. To make matters worse, 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 strong 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). So it is clear that that genetics again appear to over-power environmental factors.

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, multiple 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 wades in

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 has ceased, that the cohort of intervention children did not seek out intellectual pursuits that would match their newly (and temporary) 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 inherently genetic, 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 before, 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.

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.

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IQ and poverty: brain imaging results

IQ and poverty
IQ and poverty: brain size involved, but stresses likely culprits also

It has been long established that IQ and poverty are negatively related. In a recently study published in the journal Nature Neuroscience, Kimberly Noble (of Columbia), and Elizabeth Sowell (of Children’s Hospital in Los Angeles) imaged the brains of 1,099 children and young adults between the ages of 3 and 20 across the US and mapped the results in terms of volume of the brain to parental income brackets. Controlling for a number of confounding factors including parental education, the authors founds that the brain surfaces associated with language, memory, and executive function, were 6% larger for the children who were born to parents earning more than USD150,000 annually, relative to children whose parents earned less than USD25,000 annually. The areas of the brain that were imaged are all known to be critical to academic success. The authors also found that children from lower income families also performed more poorly on a battery of cognitive tests.

This result is consistent with a body of prior research that linked brain size (as measured by MRI scan) and cognitive ability (Luder et. al, 2008 and McDaniel 2005). In particular, McDaniels’ research paper was a meta analysis covering 37 studies and found a correlation coefficient of 0.33 between brain volume and IQ score.

But Noble and Sowell’s findings are also in line with a recent unpublished study by Martha Farah (or the University of Pennsylvania) who scanned the brains of  44 1-month old babies from African American families and found that brain sizes were also smaller than wealthier controls. Poverty and brain size are therefore negatively related variables. We know that brain size and IQ are positively related variables, which means that IQ and poverty are also negatively correlated.

The two studies were empirical in nature in that neither could advance a definitive explanation for the results, although the authors suggested that nutrition, environmental stress factors (including during the pregnancy), and a lack of resources could in fact be partly responsible for the results.

Noble and Sowell aim to go on to see whether they can replicate the results of a Mexican study by Fernald et al. (2005) in which parental incomes of poor families were supplemented to find that the cognitive abilities of children were improved within an 18 month period. An ability to replicate Fernald’s study results would be a victory for policy makers, and would no doubt, if used as a policy tool, garner the political support of nations.

IQ and poverty: what about genetics?

This set of studies is particularly interesting as neither of the authors have discuss genetic influences as possible explanatory factors for the results. Charles Murray expressed his surprise in this regard, citing that the genetic evidence presented in the Bell Curve could not be ignored when interpreting the results of this study.

A large number of recent studies have found that IQ in inheritable, with genetics found to account for a greater proportion of the variance in IQ scores relative to environmental factors. Again, the relative influence of genetics to environment is roughly 2:1. On this basis, it is somewhat surprising that Noble and Sowell would have ignored this aspect of the literature in discussing the results; although a culture does seem to be emerging in academia whereby unflattering results that are not politically correct are immediately branded as controversial and spark outcry.

The link between IQ and income is a well established one, as is the link between different professions and average IQ levels. It therefore comes as no surprise that people with higher average IQs will be able to achieve higher levels of education, which in turn will lead to a greater propensity to be in a professional job, and therefore the potential to earn a higher level of income. Professionals mating with professionals (or at the very least, university graduates getting together with other graduates) will lead to higher average IQ of offspring, which most probably perpetuates the IQ gap vs. poorer cohorts.

What is interesting with this new study is that it reveals that not only do offspring from poorer families have lower IQs, but they also have smaller brain volumes. This latter finding again would appear to reinforce the heritability of intelligence line of argumentation.

Income per se cannot be responsible for the results. Greater income does in fact offer parental scope to foster better learning environments, but alas, improving learning environments will only ever achieve so much, as genetic differences are unlikely to be able to be overcome through environmental engineering. As a society, we must work towards ensuring equal opportunity, whilst recognising that such equal opportunity is only likely to lead to unequal outcomes.

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