I’m not implying immigration leads to US decline. The pool I refer to is international. China.

Environmental factors Of China have been changing in the past 3 decades leading to extraordinary gain in IQ. This re normalizes the IQ every year which leads to what appears to be a decline in IQ in the US.

Genetics plays a part because with the economic infrastructure of China supporting students to their maximum potential it brings the playing field on par with US. China no longer has to deal with poverty effecting IQ scores.

This with environment in parity the only thing left is really genetics.