I am not so sure.
When I see old movies and photographs from the 1950's and before, Americans back then--even apart from clothing, hairstyles, and women's makeup--look different from current Americans.
Some of this could be diet and lifestyle. And some of it could be from mixing in a more diverse gene pool . . .
Still, I dunno. We might have evolved enough over the last 50+ years to be noticeable.
From my personal perspective, Americans, especially the women, got better looking up until the 1990's.
Since then, they seem to be getting uglier.
Ten thousand years from now, scientists will conclude that a comet explosion wiped out spandex and big hair at the end of the 1980s. Humanity will be preceived as vastly better off because of it. :)
Since then, they seem to be getting uglier.
Caused, ironically enough, by something called feminism...