It is astonishing how people will view the same evidence and reach diametrically opposed opinions about it.
The "almost identical genetic material" described above is precisely what Darwin was discussing in suggesting that minute changes in it would have dramatic effects. They do.
He spoke of "changes" not of "identical genetic material".
I think it is a very serious error to impute scientific knowledge to Darwin that he couldn't have had at that time.
Moslems do this to the point of distraction. They find a word in the Koran and then posit various scientific fields on top of it and ultimately credit that development to Mohammad.