![]() ![]() 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). To be clear: these findings do not mean that differences in intelligence are entirely determined by culture. 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. 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. As they develop higher levels of cognitive ability, they will also tend to achieve relatively higher levels of knowledge. Those with a proclivity to engage in cognitive complexity will tend to seek out intellectually demanding environments. 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. Instead, the best explanation may require abandoning some long held assumptions in the field. Also, this theory doesn't provide an explanation for why the heritability of IQ increases linearly from childhood to young adulthood. It's not clear why tests such as vocabulary would have a higher cognitive demand than tests that are less culturally-loaded, but more cognitively complex (e.g., tests of abstract reasoning). For this to be true, tests such as vocabulary would have to depend more on IQ than fluid intelligence. The next possibility is that the traditional investment theory is correct, and crystallized intelligence (e.g., vocabulary, general knowledge) is more cognitively demanding than solving the most complex abstract reasoning tests. The only thing that varies is cognitive ability. Everyone has the same educational experiences. One possibility is that Western society is a homogenous learning environment- school systems are all the same. Why did the most culturally-loaded tests have the highest heritability coefficients? As the researchers note, this finding "demands explanation", since it's inconsistent with the traditional investment story. The effects were medium-to-large, and statistically significant:Īs you can see above, highly culturally loaded tests such as Vocabulary, Spelling, and Information had relatively high heritability coefficients, and were also highly related to IQ. Second, in adults, the researchers found that the higher the heritability of the cognitive test, the more the test depended on culture. This finding is actually quite striking, and suggests that the extent to which a test of cognitive ability correlates with IQ is the extent to which it reflects societal demands, not cognitive demands. ![]() First, in samples of both adults and children, they found that the greater the cultural load, the greater the test was associated with IQ:* Importantly, they assessed the "Cultural load" of various cognitive abilities by taking the average percentage of test items that were adjusted when the test was adapted for use in 13 different countries.įor instance, here is the cultural load of the Wechsler Intelligence Test subtests: They investigated how heritability coefficients vary across specific cognitive abilities. In a new study, Kees-Jan Kan and colleagues analyzed the results of 23 independent twin studies conducted with representative samples, yielding a total sample of 7,852 people. 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. According to this theory, crystallized intelligence develops through the investment of fluid intelligence in a particular body of knowledge.Īs 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. ![]() 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. One of the longest standing assumptions about the nature of human intelligence has just been seriously challenged.Īccording to the traditional "investment" theory, intelligence can be classified into two main categories: fluid and crystallized. ![]()
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