Sounds to me like a case of regression to the mean. First-generation immigrants are those with enough "get up and go" to make dramatic changes in their life in the hope of improving their lot. But, as in any situation where you have a mix of heredity and randomness, the children will tend to be more average than their parents were. A simple example of this is rolling a bunch of dice (which have no 'heredity' from roll to roll), selecting all those "exceptional" ones that rolled sixes, and seeing how they do on a re-roll.

"Aw, it's just pictures of naked people."

Evolution of Gamers
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