Darwin cited several possibilities that would be "fatal to his theory". Recall that he and his age were utterly ignorant of molecular biology, which we understand as the entire basis of genetics. It's very easy to imagine any number of ways that biological evolution could have been falsified with this new knowledge. If different groups of plants or animals had incompatible genetic coding, that would do it.
Of course, just the opposite occurred, with genetic sequencing providing a sort of microscope into the details of ancestral relationships, and so providing comprehensive and spectacular confirmation of evolutionary descent.
“Darwin cited several possibilities that would be “fatal to his theory”. Recall that he and his age were utterly ignorant of molecular biology, which we understand as the entire basis of genetics.”
His theory actually never provides any explanation for heritability. What you’re talking about here is the modern synthesis, not Darwinian Natural selection. So let’s get that out of the way.
“If different groups of plants or animals had incompatible genetic coding, that would do it.”
That still doesn’t provide evidence that one is formed from the other. Elements are all common between organic and inorganic. Does it mean that if you take a rock you can get people out of it? Just because the rock has oxygen in it and you have oxygen in you doesn’t mean that you are descended from this rock.
Is it replicable. Can we take it into a lab and prove that evolution happened this way? No, it’s never been see. The assumption is that differentiation eventually leads to tramutation of a species, something that’s also not been observed either.
Also how does one define ‘compatible’. Plants don’t have a chromosomal structure to people.