Genetical and Cultural Covariance in IQ?

[ignorantianescia]

This is an old article and also from a popular science blog, but still rather interesting:

blogs.scientificamerican.com/beautiful-minds/2013/10/17/the-heritability-of-intelligence-not-what-you-think/

One of the longest standing assumptions about the nature of human intelligence has just been seriously challenged.

According to the traditional “investment” theory, intelligence can be classified into two main categories: fluid and crystallized. Differences in fluid intelligence are thought to reflect novel, on-the-spot reasoning, whereas differences in crystallized intelligence are thought to reflect previously acquired knowledge and skills. According to this theory, crystallized intelligence develops through the investment of fluid intelligence in a particular body of knowledge.

As far as genetics is concerned, this story has a very clear prediction: In the general population– in which people differ in their educational experiences– the heritability of crystallized intelligence is expected to be lower than the heritability of fluid intelligence. This traditional theory assumes that fluid intelligence is heavily influenced by genes and relatively fixed, whereas crystallized intelligence is more heavily dependent on acquired skills and learning opportunities.

But is this story really true?

The blog writer and the authors of the study to whom he refers clearly think it's probably a slightly different story:

Instead, the best explanation may require abandoning some long held assumptions in the field. The researchers argue that their findings are best understood in terms of genotype-environment covariance, in which cognitive abilities and knowledge dynamically feed off each other. Those with a proclivity to engage in cognitive complexity will tend to seek out intellectually demanding environments. As they develop higher levels of cognitive ability, they will also tend to achieve relatively higher levels of knowledge. More knowledge will make it more likely that they will eventually end up in more cognitively demanding environments, which will facilitate the development of an even wider range of knowledge and skills. According to Kees-Jan Kan and colleagues, societal demands influence the development and interaction of multiple cognitive abilities and knowledge, thus causing positive correlations among each other, and giving rise to the general intelligence factor.

To be clear: these findings do not mean that differences in intelligence are entirely determined by culture. Numerous researchers have found that the structure of cognitive abilities is strongly influenced by genes (although we haven’t the foggiest idea which genes are reliably important). What these findings do suggest is that there is a much greater role of culture, education, and experience in the development of intelligence than mainstream theories of intelligence have assumed. Behavioral genetics researchers– who parse out genetic and environmental sources of variation– have often operated on the assumption that genotype and environment are independent and do not covary. These findings suggests they very much do.

[eckadimmock]

The latter view is supported by the Flynn Effect, whereby national average IQ scores seem to increase by about 3 points per decade, too fast for it to be explained by changes in genes. www.princeton.edu/~achaney/tmve/wiki100k/docs/Flynn_effect.html

Genes only determine potential; how much of that potential is actually realised depends on environment and nurture.

[ignorantianescia]

Interesting link. The current Wikipedia page suggests that the Flynn effect is disappearing in several developed countries and reversing in some metrics. That would suggest the expression of potential is encountering some (its?) limits. Do you know if these trends are accepted in the literature?

And welcome back, eckadimmock.

[eckadimmock]

Thanks Ignorantianescia! As far as I know it's a well-known effect, but I suppose it cannot increase to infinity. It may also be a reflection of the popularity of IQ tests and related tests like SATs - children now get coached in IQ-type questions, and in general literacy and education have improved since the 1920s when the use of such tests became widespread.

Scarr and Weinburg looked at racial differences in IQ (a preoccupation of testers since the beginning) to see whether the perceived difference between US Black and White children was innate or cultural. They found that while overall African Americans scored slightly lower, but when Black children were raised in White foster homes their test scores were no different to those of Whites. I don't doubt there's a strong genetic component to intelligence, but any test involves socio-cultural judgements of what in intelligent person should be able to do.

lesacreduprintemps19.files.wordpress.com/2012/12/the-minnesota-transracial-adoption-study-a-follow-up-of-iq-test-performance-at-adolescence1.pdf

[chavoux]

I come from a "third world" country and this is also something I have been wondering about: if nobody has yet made the (to me rather obvious) connection between nutrition, brain development and IQ? Would this not also explain why the increase in IQ flattens out in developed countries (with little increase in average nutritional quality)?

[rayznack]

Feb 16, 2014 20:05:31 GMT eckadimmock said:

Thanks Ignorantianescia! As far as I know it's a well-known effect, but I suppose it cannot increase to infinity. It may also be a reflection of the popularity of IQ tests and related tests like SATs - children now get coached in IQ-type questions, and in general literacy and education have improved since the 1920s when the use of such tests became widespread.

Scarr and Weinburg looked at racial differences in IQ (a preoccupation of testers since the beginning) to see whether the perceived difference between US Black and White children was innate or cultural. They found that while overall African Americans scored slightly lower, but when Black children were raised in White foster homes their test scores were no different to those of Whites. I don't doubt there's a strong genetic component to intelligence, but any test involves socio-cultural judgements of what in intelligent person should be able to do.

lesacreduprintemps19.files.wordpress.com/2012/12/the-minnesota-transracial-adoption-study-a-follow-up-of-iq-test-performance-at-adolescence1.pdf

I can't find that whites and blacks raised by whites have the same IQ, but I did find on page 7 that after re-testing at 17 years of age, adopted white and black teens had IQ's of 105.6 and 89.4, respectively; biracial black/white children had IQ's of 98.5.

Could you please show where in the study blacks raised in white homes had no IQ differential than whites?

[ignorantianescia]

Hello rayznack. Eckadimmock hasn't been logged in for more than two years, so I don't think it's likely he'll respond to your question.

On pages 130 to 132 it is mentioned that adoptees with two black parents tended to be placed later, have a poorer placement histories and come from families with lower educational attainments. But if you compare the early placed black adoptees to white adoptees, there is only a small difference in Time 2 averages (6.4, around half the standard deviation). Also note that there's a few points difference between the Time 1a and Time 1b averages and ranges among white adoptees (6.1, while the lower range bound goes from 62 to 92), which may indicate that the population in the follow up was slightly less representative in this demographic. Maybe that's what Eckadimmock was thinking of.

Also note that sample sizes are small, which means larger error margins.

[thomashooper]

Genetic is the flow description of a gene to the corresponding protein information and protein expression. Indeed, this is a very interesting study.