A few months ago an interesting paper connected the historical demographics of New Hampshire with genetic variation. One of the notable features of North American history and culture is that it is a mosaic of different populations, and, that mosaic has come about in very different ways. For example, the millions of Italian and Jewish Americans descend from hundreds of thousands of Italian and Jewish immigrants. By contrast, millions of Yankees and Quebecois descend from tens of thousands of ancestors, who arrived in the 17th and 18th centuries. In 1992 a Census demographer, Gibson Campbell, calculated that 49% of the population of the United States in 1990 was descended from those whose ancestors were resident withi nthe United States in in 1790 in “The Contribution of Immigration to the Growth and Ethnic Diversity of the American Population” (inclusive of blacks and whites). 51% were descended from those who arrived after 1790. Put it another way, 127 million Americans in 1990 were attributable to the net 50 million immigrants who arrived after 1790. The remainder of the population would be attributable to the 4 million U.S. residents in 1790.
The mosaic of North American populations
Note: Looking at the immigration records more than 1 million Italians and Jews remained in the United States (around 4 million Italians arrived between 1820 and 1920, but the majority seem to have gone back to Italy). But reproductive variance being what it is, I think it is plausible to assuming that fewer than 1 million may contribute most to the current generations of these two groups.