What’s up with Abductions?

I think Richard Dolan might just be onto something with the hybrid angle.
But let's say the alien DNA has been in play for quite a while, then how would scientists know that the DNA wasn't "human"?
How far back would they have to go to find out when the alien DNA was introduced into the human line?

Probably not that far back I would say;-)

The X chromosome?

And why stop at humans, right?

Just sayin'.