You left out a very important ingredient in intelligence — language. Chomsky was the first to postulate language was a genetic endowment, but that was long before the arrival of genetics. Later, some people took it literally, and claimed (without any genetic proof) that language developed automatically because it was hidden in a person’s ‘genes’, and, given the ‘right’ ‘inducements’, would automatically develop, thus negating the need to learn anything. [False] After genetics arrived, a hardcore group calling itself ‘genetic linguistics’, declared it would now find the gene for language and prove Chomsky right. But it hasn’t and never will. The reason: they’re looking for something that doesn’t exist — a single set of genes for language. [This suggests a kind of ‘monism’ about language.] Your article highlights the fact that genetics is complex, not simplistic. That intelligence is hard to pin down and even harder to locate in our genetics. However, without language there is no ‘intelligence’ as we know and understand it. Without language, you would not have been able to write the article as skillfully as you did. And we ‘readers’ would not have been able to understand it if we could not read it. Genes are omnigenic, and influence everything about us. I would postulate that language is the key to ‘intelligence’, not the reverse [must have a high IQ to learn language] — as demonstrated by your ability to write such an interesting article. As we know, or should know, IQ is only correlated with language skills, and that means the opposite of what is implied in your article that without high IQs nothing else happens. However, while you quote stats that IQs rose (over a certain period, without more qualification), you didn’t quote stats that said language skills also rose over the same period. Learning language has everything to do with a loving, supportive, social environment [nurture (provided the architecture of the brain supports it)] — barring neuro-cognitive issues caused by genetic anomalies [caused in epigenetics, that I’m aware]. Remove these ‘nurture’ ingredients and intelligence becomes a mute point. Language can still be learned regardless of having a high IQ. The application of language skills is relative to the purpose it is used. A person can increase their IQ (in today’s world) as their language skills develop [learning a foreign language can be used as an example] — i.e. could you have written this article with your linguistic skills as a 10-year-old? I think the discussion of IQ as something unrelated to language verges on a perverse form of social Darwinism.
