One of the things I really hate are unqualified linear projections. They’re so useless most of the time. A science fiction magazine will give you more insight about the future than the United Nations population projection for the year 2100. This is just as much of an issue when it comes to American Census demographic projections. As I’ve noted before population projections of the coming non-Hispanic white minority 2040 to 2050 are sensitive to the assumptions behind the basic parameters. The logic of the projection is crystal clear and airtight, but just because a certain set of assumptions holds today, does not mean that those assumptions will hold indefinitely (though the Census projections are much more plausible than the United Nations projections because two generations are so much more strongly impacted by by the inertia of current conditions that four generations). In the 18th and 19th century white Americans, and especially the Anglo-Saxon founding stock, were a highly fertile folk. They took over the American Southwest and the Northwest in large part due to their demographic assault. In New England the 30,000 of 1650 became the 700,000 in 1790 in large part due to fertility rates on the order of 7 per woman! Today no one would expect that Anglo-Saxon Americans would be so fertile, let alone the New Englanders who were prominent in the population control movements of the 20th century. In the 17th and 18th century the Jews of Eastern Europe were a highly prolific group, and the gentile majority in places like Poland viewed the waxing of the proportion of this minority with great suspicion. Today no one views the Ashkenazi Jews as demographic engines, though in places like Israel the fecund Haredi have now helped close the “birth gap” with the Arab population, as its fraction of the Jewish population keeps increasing. I can give you other “counter-intuitive” examples from the recent past, but a little history goes a long way in teaching suspicion (e.g., in the Balkans in the late 19th century rural Christian populations had much higher fertility than urban Muslim ones).
These sorts of reversals are not inexplicable. Fertility shifts occur, sometimes within a generation or two. This is why Thomas Malthus turned out to be wrong: he didn’t predict the demographic transition. But we shouldn’t be complacent and assume we’ve reached the “end of history” when it comes to fertility transitions. In the early 20th century there was great terror in the American elite due to the immigration of what would later be termed “ethnic whites,” in particular Jews and Southern Europeans. And yet the Jewish proportion of the American population peaked in the late 1940s at ~5%. What about the other groups? The General Social Survey has large sample sizes for some ethnic groups, so I decided to look there.