A few observations about immigration and intelligence
In my comments on IQ, yesterday, I asked why the descendants of African slaves who have in recent decades come to the USA from the Caribbean tend to outperform in various ways the descendants of African slaves whose ancestors were transported directly to what is now the USA. Afro-Americans themselves are well aware of the difference and refer to Afro-Caribbeans as "coconuts" (brown on the outside, white on the inside).
I attributed the difference between the two groups to an immigration effect: "People who have somehow got themselves out of a Caribbean hellhole such as Jamaica or Haiti and re-established themselves in America are obviously smarter than those who stay behind in their scenic but poor, corrupt and crime-ridden homelands. So they do better in America because they are smarter to start with. They are an environmentally-selected superior subset of their parent population. Most of their success follows from that. The first generation too tend to have better motivation, having grown up in a society lacking welfare payments. It's basically work or starve where they come from. And they do of course tend to pass work-oriented values onto their kids."
A question that flows from that, however, starts from the fact that Americans generally are of immigrant origin. So why is not the average white American IQ higher than the average IQ of (say) Britain? The easy answer, of course is that Americans today originate from all corners of the globe. They are not solely of British descent and some of the incoming groups may originally have come from backward populations and thus have dragged the average down.
But let me look in a bit more detail at that: Unlike the "coconuts", the earliest white settlers in North America were NOT fleeing from backward hellholes. They were in fact fleeing from the most advanced civilizations of the day, predominantly Britain and Germany. They were fleeing mainly for religious reasons rather than economic ones and whether that indicates greater intelligence or not is I think at least not obvious. Later waves of immigration, however, clearly DID come to America for economic reasons: poor people from Ireland, Poland, Germany, Russia and Southern Italy, principally. And as Herrnstein & Murray showed long ago, there is a social class effect on IQ: Poor people tend to be dumber. So the fact that the descendants of that later wave suffer no present-day IQ disadvantage illustrates that the immigration effect DID work for them too: The immigrant poor were smarter than the poor populations that they left behind. So, just looking at the major population groups that today constitute white America, there is no reason to expect in them higher average IQs than the average IQs in (say) Britain or Germany. And the reality corresponds to that expectation.
A small coda to that which I mention with some hesitation concerns Ireland -- seeing that I myself have substantial Irish ancestry. The various 20th century studies of Irish IQ have produced some rather low averages, with a 7-point disadvantage often quoted. There are various possible reasons for that but we may be seeing there the other end of the immigration effect: For various reasons, but particularly the potato blight, the emigration from Ireland was particularly heavy and the smartest people left Ireland long ago for parts of the world with greater opportunities: principally Britain, North America and the Antipodes. I am rather glad that some of them came to the Antipodes because I would not exist otherwise. And I can assure you that I am perfectly delighted by my Irish ancestry.
And that somehow brings me to the Chinese. No-one in his right mind can deny the outstanding academic success and success generally of the Chinese in America. So is that an immigrant effect too? Are they smart solely because they are immigrants who had to overcome large difficulties in order to come to America? I think that there is some truth in that, but it is far from the whole story. The studies of IQ in China itself unfailingly show an above-average result, usually considerably above average. On the other hand, as far as I am aware, none of the studies of IQ in China come from completely representative national population samples and it may be that there are among the poor populations of the more remote regions of China some quite low averages to be found, which could well drag the national average down to something like the Western average if taken into account. But that is speculation. Clearly, the parts of China from which Chinese Americans come show above average IQs so Chinese Americans are a select subset of an already talented population. No wonder they do so well.