Suppose that extraplanetary aliens have been living on earth for centuries, mixing with earth-born humans. How would we know, and would it make a difference to know?

I was just reading various theories on the “New World Order” and the supposed goal of World Government (Planetary government) that is entailed.

One of the theories is that aliens landed here centuries ago and are slowly allowing (or perhaps encouraging) world society to move into a world government. They theory says that the aliens are playing a long game – millennia – but that the process is ongoing.

If that’s the case, how would we know who is an extraplanetary alien and who isn’t? If they’re here for generations and generations, wouldn’t they have mixed so well that we wouldn’t be able to tell?

And – would it matter?