So original sin is passed on biologically?
Sure. Why not? Everyone with original sin has been the biological child of somebody and everyone born without original sin has had some sort of "other" creation/conception.
It's a valid working theory. You think maybe test-tube babies will be able to keep the law?
I don't think "biologically" is exactly the right word, but yes. It's not something that can be found under a microscope or in the DNA. But it is a congenital condition common to all humans.
Adam and Eve were created in Eden. When they were expelled, all of their descendents have been born outside of the garden.
SD