By Jon Ray @ Dissecting Leftism
is a well-informed answer
to the above question. I disagree with his conclusion that it is all due to nutrition however. Other work finds only 5 IQ points attributable to nutrition. The suggestion of 15 IQ points is therefore startling. So I think we need to look at other possibilities. I think that the Indian advantage is probably a compound of several factors.
The treatment of Indians as a single group is of course absurd. Almost any Indian will regale you with stories about the great gaps between the castes. And the castes do seem to have a racial and historic origin. A Brahman and a Dalit are worlds apart in all sorts of ways, including skin color. And it is usually held that the differences arose from the Northern Brahmins being in fact late "Aryan" invaders on top of an original Dravidian population. So we would expect Brahmins to have higher IQs. And Brahmins seem well-represented in Indian immigrants to America.
Everything in the above paragraph is however subject to controversy so how much caste accounts for higher IQs in Indian Americans remains "under study". Something that would reveal the effect (or not) of caste would be a study of Indian diaspora populations in places such as Fiji, where the Indians there are the descendants of coolies imported to act as agricultural labourers. If they have high IQs, there is no caste effect. But I can find no data on such populations. It is however true that Indians run just about everything in Fiji these days.
The next possibility is related to the one above: A general selective effect of immigration. Diaspora populations are not always brighter than the home population but when we are looking at poor countries they probably are. To get yourself out of a poor country to a rich one surely requires brains. So regardless of caste, diaspora Indians should be brighter.
The third possibility is one shown up by the Flynn effect: Education. Education does have an effect on at least some measures of intelligence. How that works is speculative but the most plausible explanation is that doing tests and exams in the course of a long education develops test-taking skills (e.g. guessing when uncertain) that generalize to IQ tests. And the Indian education system is woeful so a transition to the less woeful U.S. system should confer an advantage.
A fourth factor that is rarely mentioned in these discussions is regional differences within India. The Indian South seems to be much brighter, particularly where mathematical ability is concerned. The great concentration of Indian IT knowledge is in Bengaluru (Bangalore), which is in the South. And it was almost entirely Southern engineers who were behind the quite remarkable Indian Mars shot.
I am not going to say much about why the Southerners are smarter but I note that they hate one-another. Keralans despise Tamils, for instance. And that is related to the long history of warfare between them. And dummies are the least likely to survive wars. So warfare has dragged up the average IQ of most of the South.
But getting back to Indians in America: I have seen no figures on it but I gather that a huge proportion of Indians came to America to work in IT. If that is so, they would mostly have come from the South -- because that is where the IT ability is. So the Indian immigrants to the USA came from a (Southern) population that was ALREADY pretty high on IQ. So from that starting point, the various advantages (already mentioned) of life in the USA could easily have added one third of a standard deviation -- which could explain what we see. It could in fact explain the whole of what we see.
And regardless of where they come from in India, being employed to work in IT is a HUGE selective pressure. To code easily in languages like C and its derivatives requires an IQ within about the top 2%. If that doesn't bring up the average, nothing would.
So I would summarize that the high IQs of Indians in the USA is the combined effect of nutrition, education, caste, an immigrant effect, an effect of regional origin and an effect of occupation.
Given the extraordinary difference in average IQ between Indians in India and Indians in America (well over one standard deviation) I think a multifactorial explanation has to be strongly indicated. But all answers at this point are speculative.