Assuming you are talking about Genealogical Adam…
Can you give me some references and quotes? Back in the 1800, they did not know that Adam could be our sole-genealogical progenitor. So I am not sure how this is possible. Can you clarify?
There is a quite a bit of textual evidence for this. It seems to be the most natural reading of Genesis 1-6. Much of the confusion appears to be mistakes in the english translation.